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Beam data measurements for dynamic wedges on Varian 600C (6 MV) and 2100C (6 and 10 MV) linear accelerators. 1995

A M Bidmead, and A J Garton, and P J Childs
Physics Department, Royal Marsden Hospital, London, UK.

The measurement of beam data for dynamic wedge dosimetry requires the integration of radiation dose at points across the radiation field during the dose delivery. The different measurement techniques required when using a linear diode array to measure beam profiles and when using ionization chambers to measure depth doses and effective wedge factors are described. The segmented treatment tables (STTS), which specify the delivered dose as a function of jaw position, are used by the control algorithm to deliver dynamic wedge fields. The reproducibility achieved using STTS is very consistent (and the stability of the accelerators is very good) so there is no significant variation in effective wedge factor or profile shape. There is a unique set of 132 STTS for each energy and design of treatment machine, which encompasses all the dynamic wedge data. There are significant discontinuities of up to 14% in wedge factors at certain field sizes. This means that wedge factors have to be measured at small increments (0.5 cm) in field size, as it is the width of the dynamic wedge field that determines the STT used. Considerable care must be taken when implementing these data on a current generation treatment planning computer.

UI MeSH Term Description Entries
D010315 Particle Accelerators Devices which accelerate electrically charged atomic or subatomic particles, such as electrons, protons or ions, to high velocities so they have high kinetic energy. Betatrons,Linear Accelerators,Accelerator, Linear,Accelerator, Particle,Accelerators, Linear,Accelerators, Particle,Betatron,Linear Accelerator,Particle Accelerator
D011879 Radiotherapy Dosage The total amount of radiation absorbed by tissues as a result of radiotherapy. Dosage, Radiotherapy,Dosages, Radiotherapy,Radiotherapy Dosages
D011880 Radiotherapy Planning, Computer-Assisted Computer-assisted mathematical calculations of beam angles, intensities of radiation, and duration of irradiation in radiotherapy. Computer-Assisted Radiotherapy Planning,Dosimetry Calculations, Computer-Assisted,Planning, Computer-Assisted Radiotherapy,Calculation, Computer-Assisted Dosimetry,Calculations, Computer-Assisted Dosimetry,Computer Assisted Radiotherapy Planning,Computer-Assisted Dosimetry Calculation,Computer-Assisted Dosimetry Calculations,Dosimetry Calculation, Computer-Assisted,Dosimetry Calculations, Computer Assisted,Planning, Computer Assisted Radiotherapy,Radiotherapy Planning, Computer Assisted
D011882 Radiotherapy, High-Energy Radiotherapy using high-energy (megavolt or higher) ionizing radiation. Types of radiation include gamma rays, produced by a radioisotope within a teletherapy unit; x-rays, electrons, protons, alpha particles (helium ions) and heavy charged ions, produced by particle acceleration; and neutrons and pi-mesons (pions), produced as secondary particles following bombardment of a target with a primary particle. Megavolt Radiotherapy,High-Energy Radiotherapy,Radiotherapy, Megavolt,High Energy Radiotherapy,Radiotherapy, High Energy
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000465 Algorithms A procedure consisting of a sequence of algebraic formulas and/or logical steps to calculate or determine a given task. Algorithm
D001703 Biophysics The study of PHYSICAL PHENOMENA and PHYSICAL PROCESSES as applied to living things. Mechanobiology
D055592 Biophysical Phenomena The physical characteristics and processes of biological systems. Biophysical Concepts,Biophysical Processes,Biophysical Phenomenon,Biophysical Process,Biophysical Concept,Concept, Biophysical,Concepts, Biophysical,Phenomena, Biophysical,Phenomenon, Biophysical,Process, Biophysical,Processes, Biophysical

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