Practical Radiation Oncology 2020 PDF

Practical Radiation Oncology Supriya Mallick Goura K. Rath Rony Benson Editors 123 Practical Radiation Oncology Supriya Mallick Goura K. Rath Rony Benson Editors Practical Radiation Oncology Editors Supriya Mallick Goura K. Rath...

Practical Radiation Oncology Supriya Mallick Goura K. Rath Rony Benson Editors 123 Practical Radiation Oncology Supriya Mallick Goura K. Rath Rony Benson Editors Practical Radiation Oncology Editors Supriya Mallick Goura K. Rath National Cancer Institute Professor, Head NCI-India All India Institute of Medical Sciences All India Institute of Medical Sciences Delhi Delhi India India Rony Benson Senior Resident Regional Cancer Centre Trivandrum Kerala India ISBN 978-981-15-0072-5    ISBN 978-981-15-0073-2 (eBook) https://doi.org/10.1007/978-981-15-0073-2 © Springer Nature Singapore Pte Ltd. 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Foreword The editors of Practical Radiation Oncology need to be commended for com- piling a succinct and informative handbook. The text integrates the technical and clinical aspects of radiation oncology. Optimal utilization of radiation as a cancer therapy requires a clear understanding of the range of issues, and this book focuses on the basic physics and technical aspects and provides infor- mation vividly to the clinician involved in radiation therapy planning, par- ticularly those who are in training and new to practice. The book has been divided into six parts, covering areas such as instruments, brachytherapy, plan evaluation, clinical cases and clinical trials. It is necessary to understand the specific physical and unique clinical applications of equipment used in radiation oncology. In the first part of the book, the practical aspects of various machines used are elaborated along with the quality assurance, personal monitoring, etc. All of these are impor- tant to understand the effective and appropriate use of radiation as a treatment modality. This leads to better clinical practice and greater confidence in rec- ommending radiation treatment with appropriate techniques in a safe and equally effective manner. Brachytherapy is an important modality of treatment, especially in several gynaecological malignancies, and it is an integral part of radiation oncology. The ‘Practical Brachytherapy’ part integrates different aspect of brachyther- apy, their basics and site-specific applications. Case selection, procedure, planning and plan evaluation are discussed. The practical tips provided in this part will be very useful to the students. The recent practice of radiation oncology has been revolutionised by tech- nological advances in radiation delivery and imaging systems. The growing impact of imaging in radiotherapy planning has provided new insights into morphological and functional status. There is no doubt that imaging consti- tutes an extremely important step in radiation therapy management. Finer aspects of plan evaluation including 3D conformal radiotherapy, IMRT and tomotherapy have been discussed. Planning images and clinical examples have also been added so as to bring further clarity into the planning aspects. The developments in cancer therapy are increasingly arising from studies in basic science, and understanding of radiobiology plays a significant role. The ‘Practical Radiobiology’ part has been presented in a concise and inter- esting way. This will serve as a comprehensive guide in radiobiology related to radiation oncology. v vi Foreword The exit examination for students appears as an insurmountable problem for them; this book is conceived and written for medical students preparing for their examination. Thirteen most relevant cases have been discussed in each chapter from an exit examination point of view and will be a useful guide for quick revision. Additionally, this will be an excellent quick refer- ence for all physicians. The last part of the book deals with relevant topics in clinical trials, trans- lational research and radiation toxicity mitigation and treatment in modern practice of radiation therapy. The individual chapters in this book are well written and superbly illus- trated. I congratulate the authors for their successful efforts, as the authors have gleaned information to make easy reading. Careful attention is given to the concepts that are crucial in understanding modern techniques. The infor- mation in this book is presented in a logical and straightforward manner, thus offering an enjoyable learning experience. It is a great honour and a privilege for me to write a foreword for this book. I am confident that many clinicians would significantly benefit from the information provided by the authors. The data indicate that radiation therapy continues to be an important modality in the treatment of malignant and a large number of benign conditions. March 24, 2019 Shyam Kishore Shrivastava Director Radiation Oncology Apollo Hospitals Navi Mumbai India Former Prof & Head Radiation Oncology Tata Memorial Hospital Mumbai India Preface Practical Radiation Oncology is long due for the radiation oncology com- munity. The radiation oncology field has witnessed a paradigm shift in the last decade and has become a highly sophisticated tech-rich branch of medi- cal science. It had become increasingly difficult to keep pace with the fast technical evolution and to know details of technical integrity of modern radia- tion oncology equipment. Radiation physics and radiobiology have also evolved to complement our knowledge. Most importantly, clinical applica- tion is now very much evidence based and versatile. All these necessitate a book to compile all the necessary information at our fingertips, particularly for those who are in training and those who have entered the arena of prac- tice. We realized these aspects and embarked on writing this book, which deals with practical aspects in practising radiotherapy. We designed the book in six parts, viz. Practical Physics and Instruments, Practical Brachytherapy, Practical Planning Aspects and Plan Evaluation, Practical Radiobiology, Clinical Cases and Other Relevant Topics. In this book, we have tried to include all the relevant information for day-to-day practice. Being a practi- cally oriented book, we have added only relevant information regarding the history of radiation oncology so as not to overburden the reader. The chapters in the ‘Practical Planning Aspects and Plan Evaluation’ part deal with practi- cal aspects of how to evaluate a plan systematically with clinical examples, so that the reader understands each concept better. The chapters on clinical cases have been added keeping in mind those preparing for examinations as to how to approach a case including investigations and differentials. Practical plan- ning aspects have also been added to each chapter including images wherever possible. These chapters have been prepared mainly for the resident in train- ing preparing for the exit examination. The journey started way back in 2016, and it took nearly 2 years to come to a meaningful end. We realized that this is not the end; rather this is the beginning of a new journey. We were very careful to deliver correct informa- tion to the best of our knowledge. We have also kept in mind that the book should benefit the students who are pursuing a career in radiation oncology. The presentation has been made very simple so that the reader is not lost in the crowd of information. At the same time, we believe that for practicing radiation oncologists the book may serve as a ready source of information. We have faced few hurdles as it is expected in any good work. However, we are delighted and feel proud that the guidance of Prof. Rath helped us immensely to overcome all these hurdles. The book would not have been vii viii Preface p­ ossible without his profound interest. First of all, we express our gratitude to All India Institute of Medical Sciences, New Delhi, as it gave us the platform to think for such a book. We are overwhelmed by the response we received from all the authors across the globe, who wholeheartedly participated in making this goal achievable in a timely manner. In particular, we express our deep sense of gratitude to Dr. Nikhil Joshi, Dr. Aruna Turaka and Dr. Kiran Turaka. This book has been prepared to the best of our knowledge but there may be mistakes and shortcomings. But we invite all the reader to come up with constructive criticism so that we can rectify such weaknesses and make this book an all-time reference. Delhi, India Supriya Mallick New Delhi, India  Goura K. Rath Trivandrum, India  Rony Benson Contents Part I Practical Physics and Instrument 1 Interaction of Radiation with Matter   3 Ashish Binjola 2 Practical Aspects of QA in LINAC and Brachytherapy 13 Seema Sharma 3 Radiation Dosimetry 21 Seema Sharma 4 Radiation Protection Practical Aspects 31 Ashish Binjola 5 Beam Modifying Devices  41 Supriya Mallick and Goura K. Rath 6 Simulators 49 Bhanu Prasad Venkatesulu 7 Telecobalt 51 Rony Benson and Supriya Mallick 8 Gamma Knife  55 Renu Madan 9 Linear Accelerator  63 Supriya Mallick and Rony Benson 10 Helical Tomotherapy 69 Supriya Mallick and Rony Benson 11 Electrons  73 V. R. Anjali 12 Proton Therapy 79 Supriya Mallick 13 Radiation Facility Development 85 Ritesh Kumar and Divya Khosla 14 Intraoperative Radiotherapy 89 Supriya Mallick and Goura K. Rath ix x Contents Part II Practical Brachytherapy 15 Evolution of Brachytherapy 95 V. R. Anjali 16 Basics of Brachytherapy and Common Radio Nucleotides 103 V. R. Anjali 17 Brachytherapy in Carcinoma Cervix  109 Prashanth Giridhar and Goura K. Rath 18 Brachytherapy in Head and Neck Cancers  117 Supriya Mallick and Goura K. Rath 19 Prostate Brachytherapy 121 Prashanth Giridhar and Aruna Turaka 20 Brachytherapy in Breast Cancer 129 Ritesh Kumar and Divya Khosla 21 Brachytherapy in Soft Tissue Sarcoma 133 Prashanth Giridhar and Susovan Banerjee 22 Surface Mould Brachytherapy  139 Rony Benson, Supriya Mallick, and Goura K. Rath Part III Practical Planning Aspects and Plan Evaluation 23 Plan Evaluation in 3D Conformal Radiotherapy 145 Subhas Pandit 24 Plan Evaluation in IMRT and VMAT 151 Sandeep Muzumder and M. G. John Sebastian 25 Plan Evaluation for TomoTherapy 157 Shikha Goyal and Susovan Banerjee 26 Plan Evaluation in LINAC Based SRS and SABR 167 Prashanth Giridhar Part IV Practical Radiobiology 27 Clinical Significance of Cell Survival Curves 171 Prashanth Giridhar and Goura K. Rath 28 6Rs of Radiation Oncology 177 Renu Madan and Divya Khosla 29 Radiosensitizers and Radioprotectors 179 Renu Madan 30 Altered Fractionation Radiotherapy 185 Supriya Mallick and Goura K. Rath 31 Therapeutic Index and Its Clinical Significance  191 Rony Benson and Supriya Mallick Contents xi Part V Clinical Cases 32 Carcinoma Cervix 195 Rony Benson, Supriya Mallick, and Goura K. Rath 33 Case Carcinoma Breast  201 Rony Benson, Supriya Mallick, and Goura K. Rath 34 Oral Cavity Carcinoma  211 Prashanth Giridhar, Supriya Mallick, and Goura K. Rath 35 Oropharynx Cancer 217 Nikhil P. Joshi and Martin C. Tom 36 Laryngeal Cancer 225 Subhas Pandit and Simit Sapkota 37 Parotid Tumour 231 V. R. Anjali 38 Extremity Soft Tissue Sarcoma 239 Supriya Mallick and Goura K. Rath 39 Orbital Tumors and Retinoblastoma  245 Kiran Turaka and Aruna Turaka 40 Carcinoma Rectum 255 Bhanu Prasad Venkatesulu 41 Carcinoma Anal Canal 259 Bhanu Prasad Venkatesulu 42 Skin Cancer 263 Nikhil P. Joshi and Martin C. Tom 43 Lymphoma 269 Rony Benson, Supriya Mallick, and Goura K. Rath 44 Carcinoma Lung 275 Sandeep Muzumder and M. G. John Sebastian Part VI Other Relevant Topics 45 Critical Appraisal of a Clinical Trial 285 Bhanu Prasad Venkatesulu 46 Radiation Toxicity 287 Supriya Mallick, Rony Benson, and Goura K. Rath 47 Cancer in India 299 Supriya Mallick, Chitresh Kumar, Rony Benson, and Goura K. Rath About the Editors Supriya Mallick is currently an Assistant Professor of Radiation Oncology at the National Cancer Institute-India, AIIMS, New Delhi. He is a graduate of Calcutta Medical College and received his MD from AIIMS. His chief research interests are in neuro-oncology and head and neck oncology. He has published numerous papers in national and international journals. Goura K. Rath is currently Director of the National Cancer Institute-India, AIIMS, New Delhi, and Chief of Dr. B R Ambedkar Institute Rotary Cancer Hospital (DRBRAIRCH) at AIIMS. He has published more than 300 papers in peer-reviewed national and international journals and is the editor of the Textbook of Radiation Oncology. Rony Benson is currently pursuing his training in medical oncology at the Regional Cancer Center, Trivandrum. His chief research interests are in gynae-oncology and head and neck oncology. He has published several papers in national and international journals. xiii  Part I Practical Physics and Instrument  Interaction of Radiation with Matter 1 Ashish Binjola The basics of physical aspects of radiation oncol- 1.1  asic Physics Concepts B ogy, radiodiagnosis, and nuclear medicine lie in to Understand Basic how various types of radiation interact with mat- Interactions ter. In radiation oncology, megavoltage X- and gamma rays and high energy electrons are used Atomic Structure An atom is a basic structure for the treatment of the malignant disease (some- from which all matter is composed, in the same times benign as well). For the simulation and way as a brick is a basic structure from which a verification of the treatment, use of kilovoltage wall is built. Atom is derived from the Greek X-rays (CT and conventional simulators, cone word Atomos means “indivisible” as it was beam CT, etc.) is a routine practice. More exotic thought to be anciently, but today we know that it heavy ion therapies, with proton (i.e., hydrogen has substructure. nucleus), carbon ion, and other heavier charged The atom is composed of: positively charged particles, are capable of providing treatment (+) protons and electrically neutral neutrons plans with higher conformality of the dose to the inside the nucleus and negatively charged (−) target volume and better normal tissue sparing. electrons orbiting around the nucleus. The Tumor biological information in the form of nucleus determines the identity of the element as PET-CT functional imaging augment for better well as its atomic mass. The nucleus constitutes delineation of target volumes in many sites/types almost 99.9% of an atom’s mass but size of the of malignancies (e.g., involved-site radiation nucleus is very small (nuclear radius is approxi- therapy). mately 10−15 m) compared to the size of the This chapter introduces the basic physics of whole atom (the size of an atom is approximately radiation interactions with the matter briefly 10−10 m), so most of the atom is empty space along with its practical aspects in radiation with electrons in fixed shells, revolving around oncology. the nucleus. Each element has a unique atomic number (number of protons inside the nucleus). Proton number never changes for any given element. For example, the Carbon atom has an atomic number of six indicating that carbon always has six protons. A. Binjola (*) Neutrons are the other constituent particles of Department of Radiation Oncology, AIIMS, the nucleus of an atom. Unlike protons and New Delhi, India © Springer Nature Singapore Pte Ltd. 2020 3 S. Mallick et al. (eds.), Practical Radiation Oncology, https://doi.org/10.1007/978-981-15-0073-2_1 4 A. Binjola e­lectrons, neutrons do not possess any charge Classification of Radiation Radiation can be (electrically neutral) classified into ionizing (having energy more than that is required to ionize an atom) and non-­ Atomic mass no A = Z + N ionizing. Visible light, radio waves (used for tele- Z- Atomic Number (number of protons inside the communications), microwaves are some nucleus); N- Number of neutrons inside the examples of non-ionizing radiations. nucleus. Electrons are negatively charged particles that Ionizing radiation can further be classified as: surround the nucleus in “orbits” or “shells.” These electrons revolve around the nucleus in 1. Directly Ionizing Radiation: Energetic well-defined orbits like planets revolving around charged particles are the directly ionizing the sun. radiation as it ionizes matter when it inter- Basic properties of atomic particles are sum- acts with atoms by ionization and excita- marized in Table 1.1. tion. Protons, alpha particles, and electrons Neutrons and protons are together called the are examples of directly ionizing nucleons and they are made up of particles known radiation. as quarks. There are six known quarks which are the 2. Indirectly Ionizing Radiation: constituent particles of hadron (protons, neutrons, Electromagnetic radiation (X-rays, gamma etc.) particles. These quarks are held inside the had- rays, and high energy spectrum of UV rays) ron particle by exchange particles gluons. The and neutrons are examples of indirectly ion- atomic structure of an atom is shown in Fig. 1.1. izing radiation. Table 1.1 Basic properties of atomic particles Atomic constituent Energy equivalence of rest particle Charge Rest mass mass Location Electron −1.6 × 10−19 9.1 × 10−31 kg 0.511 MeV/C2 Orbiting around the coulomb nucleus Proton +1.6 × 10−19 1.673 × 10−27 kg 938.28 MeV/C2 Inside the nucleus coulomb Neutron Electrically 1.675 × 10−27 kg 939.57 MeV/C2 Inside the nucleus neutral Fig. 1.1 Atomic structure: In an atom, Electrons electrons revolve around the nucleus Nucleus n p Atomic Shell or orbit 1 Interaction of Radiation with Matter 5 1.1.1 Electromagnetic Radiation ation of ion pair is called ionization. Maximum energy transfer happens during a head-on Electromagnetic radiation is the form of energy, collision. which can traverse in the vacuum with the speed If the ejected electrons have sufficient ener- c ≈ 3 × 108 m/s, in which electric and magnetic gies for further ionization, it is known as delta field vectors are orthogonal to each other as well rays. as to the direction of propagation. Speed of elec- tromagnetic radiation in the medium is lesser Specific Ionization Specific Ionization is than its speed in vacuum and depends on the defined as the number of ion pairs produced per refractive index of the medium. Figure 1.2 shows unit path length by the charged particles. Specific graphical representation of electromagnetic radi- ionization increases with the square of the charge ation waveform. of the particle and decreases with the square of the particle velocity. It is represented by lp/mm. alpha particles have higher specific ionization 1.1.2 Interaction of Charged compared to the electrons. Higher specific ion- Particles with Matter ization eventually leads to higher absorbed dose in the medium. Excitation Charged particles directly interact When highly energetic heavy charged parti- with the atomic electron and transfer energy that cles traverse the matter, specific ionization and is less than the binding energy of the electron. hence dose deposition in the medium increases to The electron goes to the higher energy state and the maximum as the particles slow down at the while returning to the ground state it emits energy end of their track. This phenomenon is responsi- in the form of electromagnetic radiation. ble for the Bragg peak of heavy charged particles. Doses to either side of the Bragg peak is quite Ionization When charged particle transfers lower compared to dose at or very near to the energy more than the binding energy of the Bragg peak. orbital electron, it ejects the electron from the When electrons pass through the matter due to atom making it positively charged, while the their lightweight, undergo multiple scattering, ejected electron is negatively charged. This cre- Direction of Electric field λ = Wavelength Direction of Magnetic field Direction of Propagation Fig. 1.2 Representation of electromagnetic radiation waveform 6 A. Binjola Fig. 1.3 Absorbed dose vs. depth for heavy charged particles Bragg Peak Absorbed Dose Depth and move in tortuous path, that is why electrons Alpha particles are comparatively heavier in do not exhibit Bragg peak (Fig. 1.3). mass and emitted with the same energy by the nuclei of a particular isotope (e.g., 4.05 MeV for Stopping Power Stopping power is the property Th-232). Alpha particles lose energy in tissue of the matter in which a beam of charged parti- very rapidly (within few micrometers). Specific cles traverses. When charged particles interact ionization and LET are very high for alpha parti- with matter, their energy loss mainly depends on cles. On the other hand, electrons are approxi- properties of the particle (mass, energy, etc.) as mately 1/7300 times lighter than alpha particle well as the absorber. For a particle beam, the rate (and 1/1840 times lighter than the proton) with of energy loss per unit path length in an absorb- unit “–”ve charge, therefore electrons are scat- ing medium is called the linear stopping power tered more easily and have a tortuous path in the (−dE/dl, usually expressed in units MeV/cm). matter. Electrons can traverse into the tissue more Dividing linear stopping power by the den- than alpha particles, with lower specific ioniza- sity ρ of the absorber results in the mass stop- tion and linear energy transfer and come to rest ping power S. (Expressed in units of MeV · cm2 after traversing the medium a distance known as · g−1). range which depends on electrons energy and the In the viewpoint of a charged particle interact- density of tissue (range of 10 MeV electrons ing with matter, we can classify stopping power from the Linac is approx. 5.0 cm in soft tissue into two types: and lesser in bone). 1. Radiative stopping power and 2. Collision stopping power 1.1.3 Radiative Interaction of Charged Particles Linear Energy Transfer (LET) It is the energy absorbed in the medium per unit path length of When a highly energetic charged particle passes the particle. LET is expressed in keV/μm. The close to the nucleus of an atom, it undergoes concept of LET is important as biological effects deflection and loses part of its energy in the form depend on the rate of energy absorption in the of electromagnetic radiation known as medium. Bremsstrahlung radiation (breaking radiation). 1 Interaction of Radiation with Matter 7 Bremsstrahlung interaction increases with the square of atomic number (Z2) of the medium and decreases with increase in the square of mass (m2) of the particle. As it is strongly dependent on the mass of the particle, heavier charged particles produce lesser amount of bremsstrahlung X-rays when compared with lighter particles. That is why electrons are the most efficient and widely used for generating X-rays. 1.2 Interaction of Electromagnetic Fig. 1.4 Rayleigh scattering: no change in the energy of Radiation scattered photon Electromagnetic radiation has neither charge nor mass and it ionizes the matter indirectly after pro- and decreases with the photon energy. ducing secondary electrons. Electromagnetic Scattered photons do not carry any informa- radiation undergoes following types of interac- tion and only degrade the image quality if tions with matter: detected. So, Rayleigh scattering is highly undesirable interaction. 1. Rayleigh scattering 2. Photoelectric absorption 3. Compton scattering 1.2.2 Photoelectric Absorption 4. Pair production 5. Pair annihilation When the X- or gamma-ray photon interacts with 6. Photodisintegration a bound electron of an atom, all the energy of the photon is transferred to the atomic electron, the The probability of these interactions depends electron is ejected from its shell and the photon is mainly upon the energy of the radiation and the completely absorbed. atomic number of the matter. The vacancy thus created by the ejection of the electron is immediately filled by outer shell electron and in this process, the energy differ- 1.2.1 Rayleigh Scattering ence between the two shells is emitted as charac- teristic X-rays (X-ray energies are characteristics It is also known as classical or coherent scat- of the atom). If the characteristic X-rays interact tering. In this type of interaction X- or γ ray with other atomic electron and electron is get- photon is absorbed by an atom following ting ejected by the absorption of the X-ray, this which it goes to higher energy state and ejects electron is called Auger electron. out the photon with the same energy in a The probability of photoelectric absorption slightly different direction, as it comes to its decreases with the increase of photon energy ground state. As there is no loss of photon (approximately ∝ 1 ) but increases as the energy taking place, it is also called inelastic E3 scattering. The probability of Rayleigh scat- atomic number of the medium increases (approx- tering (Fig. 1.4) at low KV diagnostic energy imately ∝ Z3). The probability of photoelectric range is less than 5% (e.g., mammography). absorption is the maximum when the photon This kind of interaction is more probable with energy is only slightly more than the B.E. of inner high Z material compared to low Z materials shell electron, known as the k edge. 8 A. Binjola A photon of energy hν will release an electron mode of interaction in water equivalent material with kinetic energy Ee = hν – B.E., where B.E. is for high energy photons (30 KeV to 24 MeV). the binding energy of the electron. Photoelectric absorption is the key interaction h at low diagnostic energies (Fig. 1.5). Differential ∆λ = λ ′ − λ = (1 − cos ∅ ) , mc absorption of X-rays in different body tissues is the important principle for the formation of diag- nostic images; however, at MV energies of radio- therapy, this interaction is negligible (Fig. 1.6). 1.2.3  air Production and Pair P Annihilation Compton Scattering In Compton scattering (inelastic scattering), a part of the energy of the Pair production and pair annihilation are exam- incident photon is transferred to a free electron. ples of mass and energy equivalence. Free electron means, its binding energy is very When a photon having energy more than less compared to the energy of the incident pho- 1.022 MeV interacts with the nuclear field, it gets ton. Photon transfers only a part of its energy to completely disappeared and there is a particle the electron and gets scattered at an angle with (electron) and its antiparticle (positron) known as reduced energy. Before coming to rest, the electron–positron pair. An antiparticle is same as Compton electron deposits its energy in the its particle in mass and other properties but it has medium. Compton scattering is independent of opposite charge. atomic number (Z) and depends on the electron Threshold photon energy required for the pair density of the medium. The probability of this production is 1.022 MeV. Excess energy is shared interaction decreases with increase in energy (E) as kinetic energies between the electron and the of the incident photon but it is the predominant positron. Fig. 1.5 Photoelectric Characteristic absorption X - rays Incident photon Deflected photo electron 1 Interaction of Radiation with Matter 9 Fig. 1.6 Compton Compten scattering electron θ Incident Photon φ Scattered n Photon p Positron continuously loses its energy in the inside the Linac room because of photodisinte- medium and encounters an electron & the two gration as some high energy photons when inter- particles annihilate to produce two photons in acting with Linac head causes flight, each of energy 0.511 MeV in opposite photodisintegration. direction (for the conservation of momentum). This interaction is known as the pair annihilation. The pair annihilation process is the principle 1.2.5  inear Attenuation Coefficient L behind the positron emission tomography (PET). and Mass Attenuation The probability of pair production increases Coefficient with increasing photon energy beyond the thresh- old (1.022 MeV) and also with the square of When gamma radiation traverses through matter atomic number (Z2) of the atom. There is no pair it undergoes all the described interactions with production in the diagnostic energy range, in different probabilities which depend on the megavoltage radiotherapy, pair production energy of the photons as well as on other proper- accounts for 6–20% approximately (Fig. 1.7). ties (atomic number, density, electron density, etc.) of the matter. When the radiation traverses through the mat- 1.2.4 Photodisintegration ter, its intensity reduces as it passes through the matter. For a point source of monoenergetic radi- In this interaction, a very high energy photon ation, when it passes through an absorber it (energy greater than 10 MV) interacts with the undergoes exponential attenuation. nucleus of an atom in such a way that it is com- I = I 0 e− µ x pletely absorbed by the nucleus. Nucleus goes into the excited state and there is ejection of one where I0—incident intensity of the radiation; I— or more particles (neutron, alpha particle, etc.). intensity transmitted after passing through the The probability of photodisintegration absorber; X—the thickness of the absorbing increases with photon energy and it is more prob- material; and μ—linear attenuation coefficient. able with high Z materials. If x is expressed in cm, μ is expressed in per When we treat patients using 10 MV, 15 MV, cm (cm−1) and is called linear attenuation coeffi- or higher energies, there is neutron production cient. The quantity μ/ρ is called mass attenuation 10 A. Binjola e– ε = 0.511 Mev e+ € > 1.022 e– Mev ε = 0.511 Mev e+ Pair Production Pair annihilation Fig. 1.7 Pair production and pair annihilation coefficient; where ρ is the density of the medium, undergo interaction with nuclei of the atoms. it is expressed in cm2/g. Important interactions are: Half Value Layer (HVL) and Tenth Value 1. Elastic collision Layer (TVL) The term half value layer (HVL) 2. Inelastic collision defined as the thickness of an absorber required 3. Radiative capture to attenuate the intensity of the beam to half its 4. Neutron capture (producing other particles) original value. HVL we can express using given 5. Nuclear fission formula Elastic Collision In this type of interaction total HVL = ln 2 / µ or 0.693 / µ kinetic energy of the neutron and the target nucleus TVL is the thickness of material that attenuate remains the same before and after the collision. X-ray beam by 90% and transmits only one tenth Some of the energy of the neutron is given to the of incident intensity. nucleus. As per the conservation of energy and momentum principles, the maximum energy trans- TVL = ln 10 / µ or 2.305 / µ fer will occur for the nucleus of an approximately One TVL is approximately equal to the 3.33 equal weight of the particle. That is why hydroge- HVL of attenuating material. For designing a nous materials are effective absorbers for neutrons. shielding block, approximately 5 HVL is required. Inelastic Collision When a high energy neutron 1.3 Interaction of Neurons interacts with a heavy nucleus, the neutron is with the Matter absorbed by the target nucleus and an excited compound nucleus is formed. Neutron is re-­ Interaction of neutrons: Neutrons are electrically emitted with less energy as the nucleus de-excites neutral and indirectly ionizing particles. Neutrons to ground state by emitting gamma rays. e.g., X are unaffected by coulombic fields. Neutrons (n, n γ) Y. 1 Interaction of Radiation with Matter 11 Radiative Capture Neutron is captured by the to the normal state. This kind of interaction is target nucleus and forms a compound nucleus more probable at very high energy of neutrons. which is in the excited state, and then the target nucleus decays to the ground state by emission of gamma radiation. E.g., Production of 60Co in Nuclear Fission In this process, the absorption nuclear reactor 59Co (n, γ) 60Co. Radiative capture of the neutron causes a heavy fissionable nucleus is more probable with low energy neutrons. to split into two lighter nuclei. Many fission prod- ucts (radioisotopes 99Mo, 131I, 32P, etc.) are very Neutron Capture Neutron is captured by target useful in medicine for diagnosis and therapy. nucleus and forms a compound nucleus which is Fission reaction, e.g., in an excited state due to the capture of a neutron, and then the compound nucleus emits charged U 235 + 0 n1 → 30 n1 + 36 Kr 92 + 56 Ba141 + energy particle like proton or alpha particles and comes 92  Practical Aspects of QA in LINAC and Brachytherapy 2 Seema Sharma 2.1 Introduction to doing quality assurance steps, documentation and maintaining log book is essential for each Radiotherapy treatment involves many steps radiation therapy equipment. from immobilization of the patient, imaging, Proper quality assurance at every step involv- planning, treatment, and daily verification. ing in radiotherapy can minimize the uncertain- Quality assurance at all the steps is required to ties in overall treatment delivery; thereby ensure ensure that what has been planned and prescribed, that patient gets what is planned. QA reduces being delivered to the patient. Lack of proper the probability of accidents and errors and helps quality assurance can lead to tumor under dosing in optimizing tumor control and limits normal as well as excess dose to normal tissues. tissue toxicity. Any discrepancy found during Medical physicist is primarily responsible for routine QA should be investigated and physical and technical aspects of the quality corrected. assurance. However, close coordination among physicist, technologist, and oncologist is neces- sary to ensure the quality treatment to the patient. 2.2  inear Accelerator Quality L Quality assurance (QA) starts from preparing Assurance specification for the radiotherapy equipment to be ordered. Once equipment has been purchased, 2.2.1 Acceptance of Linear acceptance test is performed to determine the Accelerator baseline standard. Radiation equipment should undergo extensive baseline checks after any Acceptance testing has to be done once the major repair to ensure the compliance with the LINAC installation is over; vendor has to per- purchase specifications. Initial calibration and form the entire test as per the requirement of the commissioning of the equipment is the next technical specification agreed at the time of pur- major step and is often time consuming. After chase. Usually vendor performs the tests as per commissioning of the equipment, periodic qual- the company’s acceptance format, after that any ity assurance steps must be done as recommended additional test or requirements as per purchase by national or international protocol. In addition order specification has to be completed. Institution physicist has to accept the LINAC technically (as per specification) before S. Sharma (*) commissioning. Department of Radiation Oncology, AIIMS, New Delhi, India © Springer Nature Singapore Pte Ltd. 2020 13 S. Mallick et al. (eds.), Practical Radiation Oncology, https://doi.org/10.1007/978-981-15-0073-2_2 14 S. Sharma Usual tests performed for acceptance testing is the responsibility of the physicist; physicist are radiation survey, jaw symmetry, coincidence will measure all the beam data (required for beam of light beam with X-ray beam, mechanical iso- modeling) and fed in to the treatment planning center stability with rotation of collimator and system as per the protocol. After measurement gantry, stability of radiation isocenter with and before using the LINAC for patient treat- respect to gantry and couch rotation, multileaf ment, physicist has to validate the commissioned collimator (MLC) quality assurance, X-ray beam LINAC along with its TPS using AAPM flatness, symmetry and percentage depth dose (American Association of Physicist in Medicine) (PDD), accuracy of optical distance indicator, TG (Task Group)-119 end-to-end test. End-to-­ table top sagging, field size indicator, etc. end test validation is necessary because if there is any problem at any step in commissioning that will be detected during end-to-end test and that 2.2.2 Commissioning of Linear will ensure that all the systems are configured Accelerator with each other properly. AAPM TG-106 gives the extensive guidelines After acceptance test, more data has to be for commissioning of medical linear accelera- acquired before clinical use of LINAC, the pro- tors. Various tests are described in TG106, some cess is known as commissioning. Commissioning major tests are tabulated in Table 2.1. Table 2.1 Major tests for commissioning a medical accelerator Data Description Calibration Dose per monitor unit calibration of all modalities and energies according to current protocol Depth dose Central axis depth dose distribution for all modalities and energies, sufficient number of field sizes to allow interpolation of data Profiles Transverse, longitudinal, and diagonal dose profiles for all modalities and energies at dmax for electrons and selected depths for photons (e.g., dmax, 5, 10, and 20 cm); all cones for electrons and selected field sizes for photons (e.g., 5 × 5, 10 × 10, and 40 × 40 cm2) Isodose distribution Isodose curves for all modalities and energies, all cones for electrons and selected field sizes for photons (e.g., 5 × 5, 10 × 10, 40 × 40 cm2), all wedge filters for selected field sizes (e.g., 5 × 5, 10 × 10 cm2, maximum) Output factors Sc, and Sp factors as a function of field size for all photon energies: output factors for all electron energies, cones, and standard inserts; tray transmission factors and wedge transmission factors Off-axis ratios A table of off-axis ratios for all photon energies as a function of distance from central axis; these data may be obtained from dose profiles for a 5 × 40-cm field at selected depths (e.g., dmax, 5, 10, 20 cm) Inverse square law Verification of inverse square law for all photon energies, virtual source position for all electron energies, and effective SSD for all electron energies and cones Tissue–phantom Direct measurement of TPRs/TMRs for all photon energies and selected field sizes (e.g., ratios 5 × 5, 10 × 10, 40 × 40 cm) and depths (5, 10, 30 cm) for verification of values calculated from percent depth doses Surface and build-up For all photon energies and selected field sizes (5 × 5, 10 × 10, 30 × 30, and 40 × 40 cm2), dose percent surface dose for all electron energies for a 10 × 10-cm cone Treatment planning Beam data input, generation, and verification of central axis percent depth dose and TPR/ system TMR tables; sample isodose curves (e.g., 5 × 5, 10 × 10, maximum) for unwedged, wedged, asymmetric, and blocked fields; sample isodose curves for multiple field plans using rectangular and elliptical contours; electron beam depth dose data; isodose curves for all cones and sample isodose curves on rectangular and circular contours Special dosimetry Data for special techniques such as total body irradiation, total skin irradiation, stereotactic radiosurgery, intraoperative electron therapy, etc. SSD source to surface distance, TMR tissue–maximum ratio, TPR tissue–phantom ratio 2 Practical Aspects of QA in LINAC and Brachytherapy 15 2.2.3  eriodic Quality Assurance P 2.3 Brachytherapy Quality of Linear Accelerator Assurance Periodic quality assurance programme is essen- Remote afterloading brachytherapy is very tial to maintain the radiation machines within its sophisticated and standard practice. Remote acceptable performance standards. Various afterloading machine minimizes the exposure to reports/publications are available on quality the personal handling the procedure. Remote assurance of linear accelerator (LINAC) and afterloading machines are available based on dif- numerous protocols are also available for special- ferent dose rates, i.e., low dose rate (LDR), high ized procedures and equipments, i.e., (1) AAPM dose rate (HDR). TG-24, Physical aspect of quality assurance in radiotherapy (1984), (2) World Health Organization quality assurance in radiotherapy 2.3.1 Acceptance of Brachytherapy (1988), (3) AAPM TG-40, Comprehensive QA (Remote Afterloading) for radiation oncology (1994), (4) IAEA, Setting up a radiotherapy program (2008), (5) AAPM Objective of performing the acceptance testing is TG-142, Quality assurance of medical accelera- to ensure that the brachytherapy equipment fulfils tors (2009), (6) AAPM, Guidance document on the purchase order specification. The acceptance delivery, treatment planning, and clinical imple- testing of the remote afterloading machine can be mentation of IMRT, (7) AAPM TG-25 and categorized in four parts as per Glasgow et al.: (1) AAPM TG-20, Recommendations for clinical operational testing, (2) radiation safety check, (3) electron beam dosimetry, (8) AAPM TG-42, testing of source calibration and transport, and (4) Stereotactic radiosurgery, (9) AAPM TG101, testing of treatment planning software. Stereotactic body radiation therapy, (10) AAPM Some recommended tests by Glasgow et al. TG-135, Quality assurance for robotic surgery, are tabulated below (Table 2.5): (11) AAPM TG-148, Quality assurance for heli- cal tomotherapy, etc. AAPM TG-142 is most widely used protocol 2.3.2  eriodic Quality Assurance P to check the LINAC performance. TG-142 report of Brachytherapy (Remote suggests various types of the tests (i.e., mechani- Afterloading) cal, radiation, safety) and the frequency of the tests with their respective tolerances. Quality assurance procedures have to be estab- Some of the tests recommended by AAPM lished for the remote afterloader unit and its TG-142 are tabulated below (Tables 2.2, 2.3, and 2.4): ancillary accessories, for the process of clinical Table 2.2 AAPM TG-142 daily QA Category Procedure Non-IMRT IMRT SRS/SBRT Dosimetry X-ray output constancy (all energies) 3% 3% 3% Dosimetry Electron output constancy (weekly test) 3% 3% 3% Mechanical Laser localization 2 mm 1.5 mm 1 mm Mechanical Distance indicator (ODI) at isocenter 2 mm 2 mm 1 mm Mechanical Collimator size indicator 2 mm 2 mm 1 mm Safety Door interlock Functional Functional Functional Safety Door closing safety Functional Functional Functional Safety Audiovisual monitors Functional Functional Functional Safety Stereotactic area monitor NA NA Functional Safety Radiation area monitor Functional Functional Functional Safety Beam on indicator Functional Functional Functional 16 S. Sharma Table 2.3 AAPM TG-142 monthly QA Category Procedure Non-IMRT IMRT SRS/SBRT Dosimetry X-ray output constancy 2% 2% 2% Dosimetry Electron output constancy 2% 2% 2% Dosimetry Backup monitor chamber constancy 2% 2% 2% Dosimetry Typical dose rate constancy NA 2% 2% Dosimetry Photon beam profile constancy 1% 1% 1% Dosimetry Electron beam profile constancy 1% 1% 1% Dosimetry Electron beam energy constancy 2%/2 mm 2%/2 mm 2%/2 mm Mechanical Light/radiation field coincidence 2 mm/1% an a 2 mm/1% an a 2 mm/1% an a side side side Mechanical Light/radiation field coincidence 1 mm/1% an a 1 mm/1% an a 1 mm/1% an a side side side Mechanical Distance check device for lasers compared 1 mm 1 mm 1 mm with front pointer Mechanical Gantry/collimator angels indicator 1.0° 1.0° 1.0° Mechanical Accessory trays 2 mm 2 mm 2 mm Mechanical Jaw position indicators (symmetric) 2 mm 2 mm 2 mm Mechanical Jaw position indicators (asymmetric) 1 mm 1 mm 1 mm Mechanical Cross-hair centering (walkout) 1 mm 1 mm 1 mm Mechanical Treatment couch position indicators 2 mm/1.0° 2 mm/1.0° 1 mm/0.5° Mechanical Wedge placement accuracy 2 mm 2 mm 2 mm Mechanical Compensator placement accuracy 1 mm 1 mm 1 mm Mechanical Latching of wedges/blocking tray Functional Functional Functional Mechanical Localization lasers 2 mm 1 mm 1 mm Safety Laser guard interlock Functional Functional Functional use of the equipment, e.g., proper execution of a extensive procedures of quality checks and their planned treatment. frequencies. Quality assurance tests are designed to con- Some of the periodic tests recommended by firm that the system (remote afterloading unit, ESTRO (European Society for Therapeutic facility, applicators, sources, etc.) performs Radiology and Oncology) Booklet-8 are tabu- within the tolerances established during the lated below (Table 2.6): acceptance tests (AAPM TG-41). In some The daily quality check should be executed cases quality assurance test procedure is identical on a routine basis before treating the first to the acceptance test procedure; on the other patient of the day. Starting the treatment may hand, less rigorous quality assurance tests are implicitly assume that daily tests were per- performed. Various protocols and guidelines are formed and that the results were satisfactory, available for periodic quality assurance. AAPM according to a department’s quality assurance Report-13, Physical Aspects of Quality Assurance protocol. User departments may develop spe- in Radiation Therapy recommends quality assur- cial daily check forms to record and sign for the ance procedures for both conventional and remote execution of these tests on satisfactory afterloaders in brachytherapy. AAPM Task Group completion. 40 has a draft document (1992) on comprehen- Brachytherapy software (treatment planning sive quality assurance procedures that includes a system) testing includes verification of dose dis- chapter on quality assurance for conventional tribution around the single and multiple sources manual brachytherapy and remote afterloaders. and matches the software generated dose distri- ESTRO Booklet-8: a practical guide to quality bution with published tables. One should also control to brachytherapy equipment gives the verify the decay correction applied by the soft- 2 Practical Aspects of QA in LINAC and Brachytherapy 17 Table 2.4 AAPM TG-142 annual QA Category Procedure Non-IMRT IMRT SRS/SBRT Dosimetry X-ray and electron flatness 1% 1% 1% change from baseline Dosimetry X-ray and electron symmetry 1% 1% 1% change from baseline Dosimetry SRS arc rotation mode; MU NA NA 1.0MU or 2% setting vs delivered Dosimetry SRS arc rotation mode; gantry NA NA 1.0 degree or 2% arc setting vs delivered Dosimetry X-ray/electron output 1% 1% 1% calibration (TG-51) Dosimetry Spot check of field size 2% for 1 mm Irradiation timer Annual > 1% Date, time, and source strength in treatment unit Daily – Transit time effect Annual – 2 Practical Aspects of QA in LINAC and Brachytherapy 19 ware with respect to standard decay table of the 2. Quality assurance of medical accelerators. AAPM Task Group 142 report. Med Phys. 2009;36(9):4197–212. source. 3. Glasgow GP, Bourland JD, Grigsby PW. A report of AAPM task group no. 41 remote afterloading technol- ogy. New York: AAPM; 1993. References 4. Holt JG. AAPM Report No. 41: remote afterloading technology. Med Phys. 1993;20(6):1761. 5. European Society For Therapeutic Radiology 1. Das IJ, Cheng CW, Watts RJ, Ahnesjö A, Gibbons J, And Oncology. Quality assurance in radiotherapy. Li XA, et al. Accelerator beam data commissioning Radiother Oncol. 1995;35:61–73. equipment and procedures: report of the TG-106 of the Therapy Physics Committee of the AAPM. Med Phys. 2008;35(9):4186–215.  Radiation Dosimetry 3 Seema Sharma 3.1 Radiation Dosimeter not have dose and dose rate dependence, directional dependence, energy response dependence, and it Radiation dosimeter is a device that measures should have high spatial resolution. An ideal dosim- directly or indirectly exposure, kerma, absorbed eter that satisfies all the above characteristics does dose or equivalent dose, or related quantities of not exist. The refore type of radiation dosimeter that ionizing radiation. The dosimetry system con- must be used, varies with measuring requirements sists of dosimeter and its reader. of the measuring situation. The radiation dosimeter must have at least one Different types of radiation measuring instru- physical property that is a function of the mea- ments consider different physical events that can sured dosimetric quantity and can be used for be utilized to make measurements. Different radiation dosimetry with proper calibration. physical events that are commonly applied in Ideal dosimeters are characterized by good accu- radiotherapy dosimetric equipments are summa- racy, precision, linearity. Ideal dosimeters should rized below (Fig. 3.1). Fig. 3.1 Physical events used for radiation Physical events used for radiation measurement measurement Ionisation Film Luminescence Semiconductor Gel S. Sharma (*) Department of Radiation Oncology, AIIMS, New Delhi, India © Springer Nature Singapore Pte Ltd. 2020 21 S. Mallick et al. (eds.), Practical Radiation Oncology, https://doi.org/10.1007/978-981-15-0073-2_3 22 S. Sharma 3.2 Ionization The wall of the thimble chamber should be air equivalent, i.e., graphite (carbon), Bakelite, 3.2.1 Free Air Ionization Chamber ­plastic with inside coating of graphite, or con- ducting mixture of graphite and Bakelite. Exact Free air ionization chamber is the primary stan- air equivalent material (atomic number same as dard for measuring exposure for superficial and air) is not possible thus difference in atomic num- orthovoltage (X-rays up to 300 Kv) (Fig. 3.2). ber is accounted in its calibration factor. Free air ionization chamber cannot be used for The volume of air contained in air cavity is the high energy photon, due to difficulty in maintain- sensitive volume of chamber. The thimble cavity ing the electronic equilibrium in the collecting contains air and air can pass on through a small volume. Therefore it can be used for superficial hole in the side of the chamber. For the measure- and orthovoltage. ment with thimble chamber the temperature and Free air ionization chamber is delicate and pressure of the air inside the cavity should be bulky, therefore cannot be used for routine mea- same as the surrounding to maintain the surements. They can be used in standardizing equilibrium. laboratories for calibration of chambers used for Thimble chamber is a secondary dosimeter low energy. and has to be calibrated against the free air ion chamber or standard cavity chamber. 3.2.2 Thimble Chamber 3.2.3 Farmer Chamber The wall of thimble chamber is like a sewing thimble; therefore it is called as thimble chamber The original Farmer chamber was developed by (Fig. 3.3). FT Farmer in 1955 (Figs. 3.4 and 3.5). By compressing the air required for electronic Framer chambers are the most commonly equilibrium its dimensions can be reduced. Air used ion chambers, for the calibration of radia- volume required for electronic equilibrium can tion therapy beams. Farmer type chamber is also be replaced by small air cavity with solid air known as cylindrical or thimble ionization equivalent wall. chamber. High voltage Secondary electron collimated beam measuring reference volume electrode Fig. 3.2 Showing the schematic diagram of free air ion chamber 3 Radiation Dosimetry 23 Fig. 3.3 Showing the Air shell Solid air shell schematic diagram of thimble chamber Air cavity Air cavity Thimble wall Insulator Central Air cavity electrode Central Outer PTCFE Insulator Graphite electrode electrode Aluminium Dural ~ 300 V Fig. 3.4 Showing the schematic diagram of Farmer chamber Fig. 3.5 Farmer chamber 24 S. Sharma An ionization chamber consists of a gas filled 1. Extrapolation chamber: cavity with a central collecting electrode sur- (a) Extrapolation chamber was designed by rounded by a conductive outer wall. A high qual- Failla in 1937. Extrapolation chamber is ity insulator separates the wall and collecting used for measuring surface dose or build- electrode to reduce the leakage current when ­up dose in a phantom (Fig. 3.6). polarizing voltage is applied to the chamber. To (b) The beam enters through a thin foil win- further reduce the chamber leakage the chamber dow that is carbon coated from inside to also contains a guard electrode. form the upper electrode. So many commercially available Farmer (c) The lower or the collecting electrode is a chambers are available, they are similar in overall small coin shaped region surrounded by a design but differ in composition of the wall mate- guard ring and is connected to an rial and central electrode. electrometer. The cavity of the chamber is vented to out- (d) The electrode spacing can be varied accu- side. The measurement with open air ionization rately by a micrometer screw. chamber requires temperature and pressure cor- (e) By measuring the ionization per unit vol- rection to account for the change in the mass of ume as a function of electrode spacing, the air in the chamber volume, which changes one can estimate the incident dose by with ­ surrounding temperature and pressure. extrapolating the ionization curve to zero Farmer type chamber has 0.6 cc nominal cavity electrode spacing. volume. 2. Parallel plate (plane-parallel) chamber: Parallel plate chamber is similar to extrapola- tion chambers except that they have a fixed 3.2.4  arallel Plate Ionization P electrode spacing (1–2 mm). Chamber (a) Parallel plate chamber has two plane walls, one serving as entry window (polar- Parallel plate chambers have two electrodes in izing electrode) and the other as back wall the shape of flat plates parallel to each other. The acting as collecting electrode (Fig. 3.7). air gap between two electrodes constitutes the (b) Usually the window is foil or 0.01–0.03 mm sensitive volume. thick Mylar, polystyrene, which allow mea- There are two kinds of parallel plate cham- surement practically at the surface of the bers: (A) the extrapolation chamber with variable phantom. Collecting electrode consists of a volume, (B) the parallel plate chamber with fixed block of conducting plastic or non-con- volume. ducting material with graphite coating. Collecting electrode Incident radiation Thin foil Guard upper electrode ring Three micrometers To electrometer Backscattering material Fig. 3.6 Showing the schematic diagram of extrapolation chamber 3 Radiation Dosimetry 25 Entrance window Direction of HT electrode radiation Air Volume 1-2 mm Guard ring Insulator Collector electrode Fig. 3.7 Showing the schematic diagram of parallel plate chamber Source Holder Air volume Electrode Well insert Source 50 mm Spacer To electrometer Fig. 3.8 Showing the schematic diagram of well type chamber (c) It also contains guard ring system. The width dardization of brachytherapy sources. of the guard ring is sufficiently large to pre- Re-entrant ion chamber is filled with air and vent electrons scattered by the side and back communicate to the outside air through a vent walls of the chamber from affecting the ion- hole. Usually calibrated in terms of reference ization in the ion collecting volume. air kerma rate. 3.2.5 Well Type Chamber 3.3 Film Sources used in brachytherapy are low air kerma rate sources that require chambers of 3.3.1 Radiographic Film sufficient volume (about 245 cc) for adequate sensitivity. This much active volume is large Radiographic X-ray film (unexposed) consists of, enough to generate sufficient ionization cur- thin plastic film coated both sides with a radiation rent which can be measured with electrometer sensitive emulsion (silver bromide, AgBr grains (Fig. 3.8). suspended in gelatin). Well type chambers are re-entrant cham- On the exposure (ionization of AgBr grains bers ideally suited for calibration and stan- take place), loosely bound electrons are freed, 26 S. Sharma Fig. 3.9 Showing the cross section of radiographic Protective layer (gelatin) film Emulsion (silver halide) Adhesive Plastic base Adhesive Emulsion (silver halide) Protective layer (gelatin) Fig. 3.10 (a) Showing the cross section of radiochromic film (b) Matte Polyester, 100 µm exposed radiochromic film Active Layer, ~28 µm Matte Polyester, 100 µm a b these electrons aggregate around impurities and active layer polymerizes, it becomes partially form negative charge. This negative charge opaque in proportion to the incident dose (Fig. 3.10). attracts Ag+ion leaving behind neutral metallic The polymer absorbs lights and transmission silver and forms the latent image in the film. of light through the film can be measured with Latent image becomes visible (film blackening) suitable densitometer. after film processing (Fig. 3.9). Radiochromic film is self-developing; there- Film gives excellent 2D spatial resolution, but fore requires no processing or developing. No useful dose range of film is limited. need of dark room and cassettes. Response of the film depends on so many fac- Radiochromic film has very high spatial reso- tors, which are difficult to control, i.e., consistent lution and dose rate independence. film processing, dark room facility. Radiochromic film does not require process- Film blackening (light transmission) can be ing but complete polymerization reaction takes measured in terms of optical density (OD) with time approximately 24 h, therefore it results in densitometers. Optical density is converted to delay between irradiation and readout. absorbed dose via calibration. Hunter and Driffield (H&D) curve is used to relate the exposure or dose to optical density. 3.3.3 Luminescence Some materials upon absorption of radiation 3.3.2 Radiochromic Film retain part of absorbed energy in metastable states. This energy is subsequently released in the Radiochromic film consists of polyester (Mylar) base form of ultraviolet, visible, or infrared light, the which is nearly a tissue equivalent composition. phenomenon is called luminescence. Radiochromic film contains a special dye that is Two types of luminescence, (i) fluorescence polymerized upon exposure to radiation. As the and (ii) phosphorescence, are known, which depend on the time delay between stimulation 3 Radiation Dosimetry 27 and emission of light. Fluorescence occurs eter is called the thermoluminescent dosimeter with time delay of 10−8 s, phosphorescence (TLD). occurs with time delay of more than 10−8 s or If the exciting agent is light, the phenome- with the suitable excitation with heat or light non is known as optically stimulated lumines- (Fig. 3.11). cence (OSL) and the dosimeter is called as Incident ionizing radiation creates the electron optically stimulated luminescent dosimeter hole pair in the crystal structure. The liberated (OSLD). electron is moved (promoted) to the conduction and migrates to the electron trap. At the same time hole migrates (along the valence band) to a 3.3.4 Thermoluminescent hole trap. Dosimeter (TLD) Energy in the form of heat for TLD or light for OSLD is given to electron and hole to escape Many TLD materials are available, the widely used from their traps. Finally electron hole pair com- TLD materials are LiF:Mg, Cu, P, LiF:Mg, Ti, bines at the luminescent center and releases CaSO4:Dy, etc. The elements mentioned after the (emits) light. TLD are the dopants or impurities. The dopants are If the exciting agent is heat, the phenomenon used to create the metastable states or traps. is called the thermoluminescence and the dosim- TLDs are available at various shapes and sizes such as powder, chip, rods, disc, and ribbon Conduction band Heat Electron trap Electron trap Impurity level Impurity level Visible light Hole trap Hole trap recombination center x-ray Valence band Fig. 3.11 Showing the schematic diagram of luminescence  28 S. Sharma depending upon their dosimetric requirement portional to temperature. This gives rise to dis- (Fig. 3.12). tinct glow peaks (Fig. 3.13). When TLD is heated, because traps differ in depth, probability of escaping from trap is pro- a b Fig. 3.12 (a) TLD chip (b) TLD badge for personal monitoring 50 3.3.5 Optically Stimulated LiF: Mg.Cu, Si Luminescent Dosimeter 40 LiF: Mg.Cu, P (OSLD) TL Intensity (a.u.) 30 Al2O3:C is sensitive OSLD and used for personal dosimetry. Light emission is achieved by 20 ­stimulating crystal with light of constant inten- sity such as LASER, LEDs, lamps, etc. 10 Emission wavelength is characteristic of OSL material, and the rate of luminescence is 0 proportional to stimulating LASER light 350 400 450 500 550 600 intensity. Temperature (K) The OSL reader integrates the photons over the period of stimulation. The stimulating light Fig. 3.13 Showing the glow curve must be prevented from being interpreted as sig- nal. OSLD reading is fast (1 s). Before reusing OSLD, bleaching treatment Heating (up to certain temperature) a TLD with light from a halogen lamp, fluorescent gives a glow curve, which is a graph of intensity lamp, or green LED has to be performed. This as a function of temperature. empties most trap centers and prepares OSLD For reuse of TLD annealing has to be done, by for reuse. which traps are emptied. For annealing process TLD Deep traps are not emptied in this process may has to be heated at 400 °C (approximately) for 1 h. be supplemented with thermal annealing. 3 Radiation Dosimetry 29 3.4 Semiconductor MOSFET, holes flow between drain and source. Whereas N-channel MOSFET, source, and drain 3.4.1 Diode Detector are composed of N-type semiconductor and gate is composed of P-type semiconductor. In Diode dosimeter is comprised of p-n junction N-channel MOSFET, electrons flow between diode, which is a junction of P-type and N-type drain and source. Only P-channel MOSFET is semiconductor. N-type semiconductors are elec- used in radiation measurement. tron donors, P-type semiconductors are electron The voltage necessary to initiate current flow acceptors. Some known impurities (called between source and drain is known as threshold volt- dopent) are added to the semiconductors to make age. When MOSFET device is exposed to radiation, P-type of N-type diodes (Fig. 3.14). electron hole pairs are generated. The difference in When radiation incident upon the sensitive voltage shift before and after the exposure can be volume or depletion layer of the diode it liberates measured and can be correlated with the dose. ions (either electron or holes). Electrons or holes Unlike TLD/OSLD, the traps cannot be emp- will start to move in sensitive volume due to tied (annealing), therefore MOSFET can be used strong electric field and induce current. This cur- for permanent dose record (Fig. 3.15). rent can be measured by electrometer and further can be calibrated for absorbed dose. 3.5 Gel Dosimeter 3.4.2 MOSFET Detector Gel dosimeters are composed of radiation sensi- tive chemical, when exposed to ionizing radiation MOSFET (Metal Oxide Semiconductor Field they undergo fundamental changes in their prop- Effect Transistor) consists of three leads, drain, erty, which is proportional to the absorbed dose. source, and gate. Gel dosimeters are 3D dosimeters and can be P-channel MOSFET, source, and drain are molded in any shape and size (Fig. 3.16). composed of P-type semiconductor and gate is Gel dosimeters are mainly two types: (1) composed of N-type semiconductor. In P-channel Fricke gel and (2) Polymer gel. a Incident Radiation b −Va+ − + Electron Hole Anode Cathode P − + n − + x=x2 x =0− x =0− x =x1 Ln W Lp Electrometer Radiation Current Fig. 3.14 (a) Showing the workflow of diode. (b) Commercially available diodes 30 S. Sharma G a b S D D P+ P+ B N P channel G S B Depletion Mode Fig. 3.15 (a) Showing the P-type MOSFET. (b) Commercially available MOSFET Fig. 3.16 Showing the gel dosimeter [image taken (with permission) from, Natanasabapathi G, et al. (2015) verifying dynamic planning in gamma knife radiosurgery using gel dosimetry. IFMBE Proceedings 2015, vol51. springer, Cham] bers for charge of photoelectrons, Compton elec- References trons and auger electrons. Radiat Prot Dosim. 2008;130(4):410–8. 1. Seco J, Clasie B, Partridge M. Review on the char- 3. Kron T, Lehmann J, Greer PB. Dosimetry of ionis- acteristics of radiation detectors for dosimetry and ing radiation in modern radiation oncology. Phys Med imaging. Phys Med Biol. 2014;59(20):R303–47. Biol. 2016;61(14):R167–205. 2. Takata N, Begum A. Corrections to air kerma and 4. Devic S, Tomic N, Lewis D. Reference radiochromic exposure measured with free air ionisation cham- film dosimetry: review of technical aspects. Phys Med. 2016;32(4):541–56.  Radiation Protection Practical Aspects 4 Ashish Binjola 4.1 Introduction Natural background radiation and the sources of man-made radiation: we are contin- Ionizing radiation has a number of applications uously exposed to low level of natural radia- that make our life better. In the field of medi- tion which is known as background radiation. cine, ionizing radiation is used in the diagnosis The source of background radiation is radioac- of disease as well as for the treatment. In the tive elements present in rocks (terrestrial radia- petroleum industry radioisotopes are used for tion), cosmic radiation from the space (the imaging oil and gas pipelines defects to avoid level of cosmic radiation increases with alti- oil or gas leakage known as nondestructive tude), etc., K40 and C12 which are the radio- analysis. Well logging, using radioactive isotopes present inside our body also add to sources is useful in determining whether a our background radiation. drilled well has certain minerals, petroleum, Medical exposure, exposure due to consumer gas, or other valuable substances. In the field items, occupational exposure, etc., which may of agriculture, radiation helps to produce high add to our radiation dose, are the sources of man-­ yield seeds for better productivity as well as made radiation. for preserving the food items for a longer dura- tion (food irradiation can delay sprouting and avoid pests in certain crops). Radiation is used 4.2 Important Organizations for sterilization of healthcare items and equip- Pertaining to Radiation ment, can help to make polymers (radiation Safety polymerization), and have numerous research applications as well in different fields of sci- (a) International Commission on Radiological ence, etc. But, on the flip side radiation can Protection (ICRP), Ottawa, Canada. pose serious health hazards, if not used in a (b) International Atomic Energy Agency planned and proper manner as advised by (IAEA), Vienna, Austria national and international regulators and advi- (c) National Council on Radiation Protection sory bodies providing regulations and guide- and Measurements, Washington, DC, USA lines for correct use of radiation. (d) The International Labour Organization (ILO), Geneva, Switzerland (e) International Commission on Radiation A. Binjola (*) Units and Measurements, USA Department of Radiation Oncology, AIIMS, (f) World Health Organization (WHO), Geneva, New Delhi, India Switzerland © Springer Nature Singapore Pte Ltd. 2020 31 S. Mallick et al. (eds.), Practical Radiation Oncology, https://doi.org/10.1007/978-981-15-0073-2_4 32 A. Binjola 4.3  asic Quantities and Units B 1 rad = 1 cGy in Radiation Safety Equivalent Dose The equivalent dose (H) is a Radioactivity Radioactivity is defined as spon- quantity which is actually derived from the taneous emission of radiation from the nucleus quantity absorbed dose, but it also takes care of of an unstable atom, and in this process, the the type of radiation as well as its energy for the unstable atom disintegrates into comparatively difference of biological effects (harm to the stable atom (either a different atom or the same body tissues). For example, a high energy alpha atom in lower energy state). The number of dis- particle or proton beam will have more harm integration the radioactive substance undergoes compared to photon beam due to its higher per unit time is known as activity (A) of the LET/specific ionization. Equivalent dose is radioactive substance. defined as: The SI unit of activity is Bq (1 disintegration H = D × WR per second) and the special unit is Ci where WR is known as the radiation weighting (1 Ci = 3.7 × 1010 Bq). factor. WR takes care of differences in biological effectiveness of different types of ionizing Exposure The quantity exposure (X) is defined radiation. as the quotient of the absolute value of total The unit of equivalent dose is Joule/Kg and its charge of the ions of either sign produced by the special name is Sievert (Sv). Another special unit of radiation (dQ) in the air by the mass of the air equivalent dose is rem (radiation equivalent man). (dm), when all the charges produced in the air are completely stopped in air, i.e., the state of elec- 1 rem = 1 cSv tronic equilibrium exists.