Radiotherapy Simulators and CT PDF

G Simulators and CT Simulators ❑ Simulators and CT simulators cover several important steps in the radiotherapeutic process related to: ❑ Determination of target location within the patient. ❑ Determination of the target shape and volume. ❑ Determination of the location of...

G Simulators and CT Simulators ❑ Simulators and CT simulators cover several important steps in the radiotherapeutic process related to: ❑ Determination of target location within the patient. ❑ Determination of the target shape and volume. ❑ Determination of the location of critical structures adjacent to treatment volume. ❑ Planning of dose delivery procedure (treatment planning). ❑ Accuracy of dose delivery to the target. M.Sc. Medical Physics Dr. Khalid I Hussein  i2 5 / fil so Radiotherapy Simulator ❑ Radiotherapy simulator consists of a diagnostic x- ray tube mounted on a rotating gantry to simulate geometries of isocentric teletherapy machines and isocentric linacs. · Y j, & - · Si :53 n M.Sc. Medical Physics Dr. Khalid I Hussein Fluoroscopic Simulation M.Sc. Medical Physics Dr. Khalid I Hussein  & Kup 2015s my Radiotherapy Simulators ❑ The simulator enjoys the same degrees of freedom as a megavoltage therapy machine, however: YS. ❑ Rather than providing a megavoltage beam for dose delivery. assels ❑ It provides a diagnostic quality x-ray beam suitable for planar imaging (fluoroscopy and radiography) and cone beam CT. · - M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy Simulators Pastor ❑ In megavoltage machines, radiation fields are defined with collimators (upper and lower jaws). basic ❑ In&simulators radiation fields (square and rectangular) are indicated with delineator wires while the radiation field, defined with a collimator, provides a field that 55s. exceeds in size the delineated field to enable visualization of the target as well as healthy tissues adjacent to the target. M.Sc. Medical Physics Dr. Khalid I Hussein  Radiotherapy Simulators 55 ❑Modern simulator covers the following processes: ·nig 2 31 , = 93 , · ❑Tumour and adjacent normal tissue localization. ❑Treatment simulation.⑫S To ❑Treatment plan verification. d > - ❑Monitoring of treatment. 2/ 2x419 - 9 ❑Components of radiographic simulators: fur ❑Imaging source & detector. - ❑Localizing lasers. 3 ❑Optical distance indicator. ❑Field light. jig? gponig's ❑Patient support assembly M.Sc. Medical Physics Dr. Khalid I Hussein  A flat table surface ensures the patient’s position during simulation is the same as during treatment.on a megavoltage machine Radiotherapy CT Simulator. % 359 * ❑CT simulators are CT scanners equipped with special features dedicated to the radiotherapy process, such as: ❑ Flat table top surface to provide a patient position during simulation that will be identical to the position during treatment on a megavoltage machine. -Y ❑ Laser marking system to transfer the coordinates of the tumour isocentre to the surface of the patient. 35: g - ❑ Virtual simulator consisting of software packages to allow the user to define and calculate a treatment isocentre and $1/s then simulate a treatment using digitally reconstructed I-S To radiographs (DRRs). - M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy CT Simulator ❑Oncology CT simulator (Philips) ❑Bore opening: 85 cm ❑Flat table top M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy CT Simulator - -- M - The major steps in the target localization and field design are: ❑Physical simulation = ga i (1) Acquisition of the patient data set. - (2) Localization of target and adjacent structures. (3) Definition and marking of the patient coordinate system. g5 o ❑Virtual simulation (1) Design of treatment fields. (2) Transfer of data to the treatment planning system (TPS). (3) Production of images used for treatment verification. M.Sc. Medical Physics Dr. Khalid I Hussein  VI Radiotherapy CT Simulator ❑CT simulation process: ❑Patient data set is collected and target localization is carried out using CT axial images. - ❑Laser alignment system is used for marking. - ❑Virtual simulator software package is used for field design and - production of-verification images (DRRs). ❑Transfer of patient data to the TPS is achieved electronically. tretmanty sti e => M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy CT Simulator ❑ Digitally reconstructed radiograph (DRR) is the digital equivalent of a planar simulation x-ray film. - - ❑ DRR is reconstructed from a CT data set using virtual simulation software available on CT simulator or on TPS tretment planning = - & sisty mu - 95 -, ❑ DRR represents a computed radiograph of a virtual patient generated from a CT data set representing the actual patient. - => ❑ Like a conventional radiograph, the DRR accounts for beam - divergence. => M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy CT Simulator Virtual Simulation - 3 - ,1 > ❑ Synthetic radiographs can be produced by tracing ray- lines from a-virtual source position through the CT data of - - the patient to a virtual film plane and simulating the attenuation of x-rays. - 7 - ❑ Synthetic radiographs are called Digitally Reconstructed Radiographs (DRRs).- ❑ Advantage of DRRs is that anatomical information may be used directly in the determination of treatment field parameters. · a s5 Radiotherapy CT Simulator or ❑Typical DRR M.Sc. Medical Physics Dr. Khalid I Hussein  Radiotherapy CT Simulator Beam’s eye view (BEV) - ❑ Beam’s eye views (BEV) are projections through the patient onto a virtual film plane perpendicular to the beam direction -- ⑧ ❑ BEVs are frequently superimposed onto the corresponding DRRs resulting in a synthetic representation of a simulation -- radiograph. > - -  Class activity (Group 3 presentation) ❑ Advantages (or disadvantages) of each type of simulator? ❑Fluoroscopic ❑CT? ❑Ultrasound ❑MRI? M.Sc. Medical Physics Dr. Khalid I Hussein  SHIELDING CONSIDERATIONS ❑ External beam radiotherapy is carried out mainly with three types of equipment that produces either x rays or electrons for clinical - use: L ❑ X-ray machines (superficial or orthovoltage). L L ❑ Cobalt-60 teletherapy machines. - L ❑ Linacs. L ❑ All radiotherapy equipment must be housed in specially shielded treatment rooms in order to protect personnel and general public in areas adjacent to the treatment rooms. M.Sc. Medical Physics Dr. Khalid I Hussein  SHIELDING CONSIDERATIONS ❑ During the planning stage for a radiotherapy machine installation, a qualified medical physicist: ❑ Determines the required thickness of primary and secondary barriers ❑ Provides the information to the architect and structural engineer for incorporation into the architectural drawing for the treatment room. M.Sc. Medical Physics Dr. Khalid I Hussein  ↳e SHIELDING CONSIDERATIONS ❑Superficial and orthovoltage x-ray therapy rooms are shielded: &si , ❑ Either with ordinary concrete (density: 2.35 g/cm3) - - ❑ Or lead (density: 11.36 g/cm3, atomic number: 82) - bes prising , a ❑In this energy range the photoelectric effect is the predominant mode of photon interaction with matter, making the use of lead very efficient for shielding purposes. - M.Sc. Medical Physics Dr. Khalid I Hussein  regi SHIELDING CONSIDERATIONS Ja ❑ Megavoltage treatment rooms are often referred to as bunkers because of the large primary and secondary barrier thicknesses required for shielding.. ❑ Megavoltage bunkers are most commonly shielded with ordinary concrete so as to minimize construction cost. = -. i9 9) ❑ The Compton effect is the predominant mode of photon interaction with shielding material in the megavoltage energy region. The barrier thickness is thus scaled inversely with density of the shielding material. When the density of the shielding material increases, the need for the barrier & ”.thickness decreases M.Sc. Medical Physics Dr. Khalid I Hussein  Wh SHIELDING CONSIDERATIONS 33159 m %B · ❑Typical teletherapy installation: isocentric machine Oreisin ❑ Primary barriers shield against the e primary radiation beam. ❑ Secondary barriers D shield against leakage radiation and ⑤ radiation scattered > from the patient. M.Sc. Medical Physics Dr. Khalid I Hussein Modern techniques in radiotherapy 24  F jin · gass. STEREOTACTIC IRRADIATION · s j & ME ❑Stereotactic irradiation comprises focal irradiation techniques that use ↑ · T , To multiple, non-coplanar photon radiation beams and deliver a prescribed dose of ionizing radiation to pre-selected and stereotactically localized lesions. 11. ❑Equipment for stereotactic radiosurgery: as -3) - ▪ Stereotactic frame: defines a fixed coordinate system for an accurate localization and irradiation of the planning target volume (PTV). ▪ Imaging equipment (CT, MRI and DSA) with which the structures, lesions and PTVs are visualized, defined and localized. - ▪ Target localization software: used in conjunction with the stereotactic frame system and imaging equipment to determine the coordinates of the target in the stereotactic reference system. ▪ Treatment planning system: calculates the 3-D dose distribution and superimposes it onto the patient’s anatomical information. ▪ Appropriate radiation source and radiosurgical treatment technique. 25 M.Sc. Medical Physics Dr. Khalid I Hussein  Dis &Y STEREOTACTIC IRRADIATION Is ❑Stereotactic frame 26 M.Sc. Medical Physics Dr. Khalid I Hussein  & 25 245 % STEREOTACTIC IRRADIATION tumen. She brain Y - ❑Radiosurgery is carried out mainly with - V- ❑Gamma Knife machines, but a significant number of radiosurgical procedures is also carried out with modified isocentric linacs and Cyberknife machines. Vis ❑CyberKnife incorporates a miniature linac mounted on a robotic arm. It is in clinical operation since the mid 1990s and in 2005 there were over 50 of these machines in clinical operation around the world. For target localization: CT and MRI 29 M.Sc. Medical Physics Dr. Khalid I Hussein  ⑤1518241mm CONFORMAL RADIOTHERAPY ❑Basic of conformal radiotherapy is that, in comparison with traditional dose delivery techniques, treatment outcomes will be improved by using special techniques that allow maximum target dose (improved tumor control probability) while maintaining an acceptable level of normal tissue complications. = --2.50 ❑Conformal radiotherapy conforms or shapes the prescription dose volume to the planning target volume - - (PTV) while at the same time keeping the dose to specified organs at risk below their tolerance dose. 95ggi -99 % j, je ⑤ 32 M.Sc. Medical Physics Dr. Khalid I Hussein  CONFORMAL RADIOTHERAPY · Si 0 /- = 55 Target localization is achieved through: & - ❑Anatomical imaging such as: - 7 ❑Computerized tomography (CT).L : ❑Magnetic resonance imaging (MRI).~ ❑Single photon emission tomography (SPECT).L ❑Ultrasound (US).Lu ❑Functional imaging such as: s & Jodie S - ❑Positron emission tomography (PET).2 ❑Functional magnetic resonance imaging (fMRI). w ❑Molecular imaging. L ‫ الوظيفة الحيوية تعني األنشطة التي يقوم بها‬،‫إذن‬ ‫ أو حاجته‬،‫ تدفق الدم‬،‫الورم مثل استهالك الجلوكوز‬ ‫ وهي تعطي األطباء فكرة عن مدى نشاط‬،‫لألكسجني‬.‫الورم وتقدمه‬ 34 M.Sc. Medical Physics Dr. Khalid I Hussein  -199 CONFORMAL RADIOTHERAPY ---- Treatment planning process for 3-D CRT consists of 4 steps: - ❑Acquisition of anatomic information in the form of transverse (axial) images. - - Wibl :I ❑Determination of the planning target volume (PTV) by the radiation oncologist by contouring the PTV on each - individual axial image (segmentation process). ❑Design of radiation fields using the-beam’s-eye-view option in the treatment planning software. ❑Optimization of the treatment plan through the design of - optimal field sizes, beam directions, beam energies, etc. - - - 20in - 35 M.Sc. Medical M.Sc. Medical Physics Physics Dr. Khalid Dr. Khalid II Hussein Hussein  CONFORMAL RADIOTHERAPY - 51 , · S gig ❑Modern linacs are equipped with MLCsjthat incorporate from 20 to 60 pairs of narrow, closely tungsten leaves, each leaf projecting a typical width of between 5 and 10 mm at & the linac isocentre. - 95 ❑MLCs projecting leaf widths less than 5 mm at the isocentre are referred to as microMLCs. They are used for: - ❑Shaping irregular fields of less than 10 cm in maximal - field dimension, such as head and neck fields. - - ❑Irregular fields with less than 3 cm in largest dimension > - that are used in radiosurgery. - 36 M.Sc. Medical Physics Dr. Khalid I Hussein  · Intensity modulated radiotherapy ❑Radiation beams in standard external beam radiotherapy including 3-D conformal radiotherapy usually have a- uniform i intensity across the field, fulfilling the linac flat-ness and symmetry specifications. ❑Non-uniform beam intensities (intensity modulation) can be used to improve dose distributions by: · ❑Compensating for contour irregularities ❑Compensating for tissue inhomogeneities - ❑Compensating for highly irregular target volumes & ❑Sparing volume. organs at risk located in the vicinity of target 37 M.Sc. Medical Physics Dr. Khalid I Hussein  - Intensity modulated radiotherapy ❑Physical wedges and compensators have long been used to produce simple - - - intensity modulation to compensate for contour irregularities. Their effects - are incorporated into a treatment plan through the use of forward planning algorithms. - ❑Modern radiotherapy techniques based on computer-controlled intensity - modulation systems have been developed during the past decade and currently represent the most sophisticated 3-D conformal dose delivery process. ❑The 3-D CRT technique which relies on multiple beams with optimized intensity modulated fluence distributions is referred to as intensity - modulated radiotherapy (IMRT). - ❑Two techniques are currently available for IMRT dose delivery: ❑Tomotherapy unit. - ❑Isocentric linac in conjunction with a multileaf collimator gist ↑ M.Sc. Medical Physics Dr. Khalid I Hussein 38