Radiotherapy Lecture Notes PDF

RADIOTHERAPY II Dr. Anastasia Hadjiconstanti Acknowledgements: Dr. Constantinos Zervides LECTURE LOB’S 54. OUTLINE THE PURPOSE OF CONFORMAL RADIOTHERAPY. 55. EXPLAIN THE CRITERIA FOR SELECTING SUITABLE ISOTOPE SOURCES FOR RADIOTHERAPY. PARTICLE ACCELERATORS I Numerous types of accelerator have been...

RADIOTHERAPY II Dr. Anastasia Hadjiconstanti Acknowledgements: Dr. Constantinos Zervides LECTURE LOB’S 54. OUTLINE THE PURPOSE OF CONFORMAL RADIOTHERAPY. 55. EXPLAIN THE CRITERIA FOR SELECTING SUITABLE ISOTOPE SOURCES FOR RADIOTHERAPY. PARTICLE ACCELERATORS I Numerous types of accelerator have been built for basic research in nuclear and high energy physics. Most of them have been modified for use in radiotherapy. Irrespective of the accelerator type, two basic conditions must be met for particle acceleration: the particle to be accelerated must be charged and an electric field must be provided in the direction of particle acceleration. PARTICLE ACCELERATORS II What distinguishes the various types of accelerator is: the way they produce the accelerating electric field and how the field acts on the particles to be accelerated. As far as the accelerating electric field is concerned there are two main classes of accelerator: electrostatic and cyclic. Examples of electrostatic accelerators used in medicine are superficial and orthovoltage X ray tubes and neutron generators. PARTICLE ACCELERATORS III The best-known example of a cyclic accelerator is the linear accelerator (LINAC). Other examples are microtrons, betatrons and cyclotrons. LINACS I Medical LINACS are cyclic accelerators. They accelerate electrons to kinetic energies from 4 to 25 MeV. In a LINAC the electrons are accelerated following straight trajectories. They do so in special evacuated structures called accelerating waveguides. LINACS II Electrons follow a linear path through the same, relatively low, potential difference several times. High power RF fields are used for electron acceleration. Various types of LINAC are available for clinical use. Some provide X rays only in the low megavoltage range (4 or 6 MV). Others provide both X rays and electrons at various megavoltage energies. A typical modern high energy LINAC will provide two photon energies (6 and 18 MV) and several electron energies (e.g. 6, 9, 12, 16 and 22 MeV). LINACS AND SAFETY I The complexity of modern LINACS raises concerns regarding operational safety. The International Electrotechnical Commission (IEC) publishes international standards. The IEC statement on the safety of LINACS is as follows: “The use of electron accelerators for radiotherapy purposes may expose patients to danger if the equipment fails to deliver the required dose to the patient, or if the equipment design does not satisfy standards of electrical and mechanical safety. The equipment may also cause danger to persons in the vicinity if the equipment fails to contain the radiation adequately and/or if there are inadequacies in the design of the treatment room.” LINACS AND SAFETY II The IEC document addresses three categories of safety issues: electrical, mechanical and radiation. It establishes specific requirements in the design and construction of LINACS for use in radiotherapy. It also covers some radiation safety aspects of LINAC installation in treatment rooms. LINACS AND SAFETY III LINAC COMPONENTS I LINACS are usually mounted isocentrically and the operational systems are distributed over five major and distinct sections of the machine, the: gantry, gantry stand or support, modulator cabinet, patient treatment table, control console. LINAC COMPONENTS II LINAC COMPONENTS III TREATMENT HEAD LINAC COMPONENTS IV The length of the accelerating waveguide depends on the final electron kinetic energy. It ranges from ≈30 cm at 4 MeV to ≈ 150 cm at 25 MeV. The main beam forming components of a modern medical LINAC are usually grouped into six classes: I. Injection system (Electron gun). IV. Auxiliary system (shielding, vacuum pump, cooling system etc.). II. RF power generation system. V. Beam transport system. III. Accelerating waveguide. VI. Beam collimation monitoring system. and beam CONFORMAL RADIOTHERAPY I In conformal radiotherapy tumour control can be improved. This is accomplished by using special techniques that allow delivery of a higher dose with acceptable normal tissue complications. Conformal radiotherapy conforms or shapes the prescription dose volume to the planning target volume (tumour). At the same time it keeps the dose to specified organs at risk below their tolerance dose. The conformal radiotherapy chain is based on: 3-D target localization, 3-D treatment planning and 3-D dose techniques. delivery CONFORMAL RADIOTHERAPY II Target localization is achieved through anatomical and functional imaging. CONFORMAL RADIOTHERAPY III Treatment planning is achieved either with: standard forward planning techniques or, design uniform intensity beams shaped to the geometrical projection of the target. advanced conformal radiotherapy techniques. inverse planning is used in addition to beam shaping. Uses intensity modulated beams to improve target dose homogeneity and spare organs at risk. CONFORMAL RADIOTHERAPY IV Dose delivery techniques range from: the use of standard regular and uniform coplanar beams, to intensity modulated non-coplanar beams produced with multi leaf collimators. BRACHYTHERAPY I Brachytherapy is a term used to describe the short distance treatment of cancer with radiation from small, encapsulated radionuclide sources. This type of treatment is given by placing sources directly into or near the volume to be treated. The dose is then delivered continuously over a short period of time or over the lifetime of the source to a complete decay. Most common brachytherapy sources emit photons. BRACHYTHERAPY II There are two main types of brachytherapy treatment: Intracavitary. Sources are placed in body cavities close to the tumour volume. Interstitial. Sources are implanted within the tumour volume. BRACHYTHERAPY III Intracavitary treatments are always temporary with short duration. Interstitial treatments may be temporary or permanent. Temporary implants are inserted using manual or remote after loading procedures. The physical advantage of brachytherapy is the improved localized delivery of dose to the target volume of interest. The disadvantage is that brachytherapy can only be used in cases in which the tumour is well localized and relatively small. In a typical radiotherapy department about 10–20% of all radiotherapy patients are treated with brachytherapy. BRACHYTHERAPY IV Several aspects must be considered when giving brachytherapy treatments. The way the sources are positioned relative to the volume to be treated is important. Several different models have been developed over the past decades for this purpose. The advantage of using a well-established model is that one benefits from the long experience associated with them. The use of uniform models and methods in brachytherapy treatments simplifies comparison of treatment results. BRACHYTHERAPY V A treatment does not reach its goals if the source misses its aimed positions by a large margin (geometrical misses). Because of the steep dose gradient that characterizes brachytherapy, geometrical misses may be detrimental. Thus there is a need for a quality control programme guaranteeing that the treatment is given in accordance with its purposes. Brachytherapy dose delivery can result in complex dose rate effects that may influence the therapeutic outcome. BRACHYTHERAPY VI The continuous delivery of dose will influence: the repair of sub lethal and potentially lethal damage, cell proliferation and other cell kinetics. All of the above can modify the radiation response of tumour and normal tissues. BRACHYTHERAPY VII BRACHYTHERAPY VIII BRACHYTHERAPY IX The choice of an appropriate photon emitting radionuclide for a specific brachytherapy treatment depends on: Photon energies. Photon beam penetration into tissue and shielding materials. Half-life. Half-value layer (HVL) in shielding materials. Specific activity. Source strength. Inverse square fall-off of dose with distance from the source. LOW DOSE RATE (LDR) BRACHYTHERAPY PERMANENT SEED IMPLANT HIGH DOSE RATE (HDR) BRACHYTHERAPY I HIGH DOSE RATE (HDR) BRACHYTHERAPY II https://youtu.be/rZ7_4vUH15k EXERCISE FOR HOME - SBA A patient suffering from prostate cancer will be treated with LDR brachytherapy. Permanent Iodine-125 seed implants will be inserted in the prostate. Which characteristic makes Iodine-125 an appropriate choice for the above treatment? A. Alpha emitter. B. Half-life of few hours. C. Large HVL. D. Low photon energy. E. Proton emitter. EXERCISE FOR HOME – SBA SOLUTION A patient suffering from prostate cancer will be treated with LDR brachytherapy. Permanent Iodine-125 seed implants will be inserted in the prostate. Which characteristic makes Iodine-125 an appropriate choice for the above treatment? A. Alpha emitter. B. Half-life of few hours. C. Large HVL. D. Low photon energy. E. Proton emitter. SUMMARY I Numerous types of accelerator have been built. Irrespective of the accelerator type, two basic conditions must be met for particle acceleration: the particle to be accelerated must be charged and an electric field must be provided in the direction of particle acceleration. What distinguishes the various types of accelerator is: the way they produce the accelerating electric field and how the field acts on the particles to be accelerated. SUMMARY II Medical LINACS are cyclic accelerators. They accelerate electrons to kinetic energies from 4 to 25 MeV. A typical modern high energy LINAC will provide two photon energies (6 and 18 MV) and several electron energies (e.g. 6, 9, 12, 16 and 22 MeV). In conformal radiotherapy tumour control can be improved. This is accomplished by using special techniques that allow delivery of a higher dose with acceptable normal tissue complications. Conformal radiotherapy conforms or shapes the prescription dose volume to the planning target volume (tumour). SUMMARY III Brachytherapy is an important modality in the treatment of malignant disease. It allows conformal treatment without heavy technological involvement. However, since it generally involves invasive procedures, it is relegated to second place behind external beam radiotherapy in the treatment of malignant disease. The basic principles of brachytherapy have not changed much during the past 100 years of radiotherapy. But, the advent of remote after loading brachytherapy has made brachytherapy much more efficient. SUMMARY IV The choice of an appropriate photon emitting radionuclide for a specific brachytherapy treatment depends on: Photon energies. Photon beam penetration into tissue and shielding materials. Half-life. Half-value layer (HVL) in shielding materials. Specific activity. Source strength. Inverse square fall-off of dose with distance from the source. REFERENCES Authors T. Pawlicki, D.J. Scanderbeg and G. Starkschall E.B. Podgorsak Title Edition Hendee’s Radiotherapy Physics 4th Edition Radiation Physics for Medical Physicists Intermediate Physics for Medicine and Biology 3rd Edition Springer 2016 9783319253824 5th Edition Springer 2015 9783319126814 1st Edition Springer 2014 9783319068404 2nd Edition CRC Press 2009 9781584889434 IAEA 2005 9201073046 R. K. Hobbie and B. J. Roth D.S. Chang, F. D. Lasley, I.J. Das, M. S. Basic Radiotherapy Physics and Mendonca and J. R. Biology Dynlacht Introduction to Physics in Suzanne Amador Kane Modern Medicine Radiation Oncology Physics: A E. B. Podgorsak handbook for teachers and students 1st Edition Publisher Year Wiley-Blackwell 2016 ISBN 9780470376515