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Collimator-related radiation dose for different cobalt machines and linear accelerators
1Dr. Bernard Verbeeten Institute for Radiation Oncology and Nuclear Medicine, Department of Clinical Physics, Tilburg, The Netherlands.
Summary
Peripheral dose (PD) measurements for radiotherapy machines show minor variations in leakage radiation. Collimator scatter dose can differ, but overall PD differences are negligible for individual patient treatment planning.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Equipment
Background:
- Previous studies established peripheral dose (PD) measurements for 60Co gamma radiation and 25 MV photons.
- Observed agreement with other investigators suggested consistent collimator leakage and scatter contributions across different machines.
Purpose of the Study:
- To investigate the assumption that radiation leakage and collimator scatter contributions to the peripheral dose (PD) are similar across different manufacturers' treatment machines.
- To validate the consistency of peripheral dose measurements in radiotherapy.
Main Methods:
- A survey was conducted among radiotherapy departments in the Netherlands and Belgium to collect peripheral dose (PD) measurements.
- Standardized measurement geometries were provided, including specific field sizes, distances, and collimator angles for various photon energies.
Main Results:
- Data from 4 cobalt machines and 37 linear accelerators (7 manufacturers) were collected, totaling 56 datasets across 12 photon energies.
- While leakage radiation dose variation was small, collimator scatter dose showed up to 50% differences between 0 and 90 degrees collimator angles, influenced by design.
- Dual energy machines exhibited higher values at high energies, and older cobalt machines showed increased leakage radiation compared to modern ones.
Conclusions:
- Peripheral dose (PD) measurements revealed no significant variation in leakage radiation dose among different accelerator makes.
- Some machines exhibited higher collimator scatter dose, yet these values remained within regulatory limits.
- Considering both collimator-related radiation and patient scatter, the observed differences in peripheral dose (PD) are considered negligible for individual patient treatment planning.