CT Simulators and Radiotherapy PDF

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 crit...

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 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. M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy Simulators ❑ The simulator enjoys the same degrees of freedom as a megavoltage therapy machine, however: ❑ Rather than providing a megavoltage beam for dose delivery. ❑ 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 ❑ In megavoltage machines, radiation fields are defined with collimators (upper and lower jaws). ❑ In simulators radiation fields (square and rectangular) are indicated with delineator wires while the radiation field, defined with a collimator, provides a field that 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 ❑Modern simulator covers the following processes: ❑Tumour and adjacent normal tissue localization. ❑Treatment simulation. ❑Treatment plan verification. ❑Monitoring of treatment. ❑Components of radiographic simulators: ❑Imaging source & detector. ❑Localizing lasers. ❑Optical distance indicator. ❑Field light. ❑Patient support assembly M.Sc. Medical Physics Dr. Khalid I Hussein Radiotherapy CT Simulator ❑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. ❑ Laser marking system to transfer the coordinates of the tumour isocentre to the surface of the patient. ❑ Virtual simulator consisting of software packages to allow the user to define and calculate a treatment isocentre and then simulate a treatment using digitally reconstructed 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 The major steps in the target localization and field design are: ❑Physical simulation (1) Acquisition of the patient data set. (2) Localization of target and adjacent structures. (3) Definition and marking of the patient coordinate system. ❑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 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. 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 ❑ 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 ❑ 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. ❑ 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.  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 ❑ BEVs are frequently superimposed onto the corresponding DRRs resulting in a synthetic representation of a simulation radiograph.