Dosimetric Tranferability of a Medical Linear Accelerator Mounted Mini-Beam Collimator
Date
2017-01-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-0692-8403
Type
Thesis
Degree Level
Masters
Abstract
The goal of this study was the dosimetric characterization of a mini-beam collimator on three clinically beam matched Varian iX linear accelerators. Measurements of the beam quality (%DD(10)), peak-to-valley dose ratio (PVDR), collimator factor (CF), and relative output factor (OF) were carried out for 2 cm x 2 cm, 3 cm x 3 cm, 4 cm x 4 cm, and 5 cm x 5 cm mini-beam collimated 6 MV fields on each linear accelerator. As well, Monte Carlo simulation of the mini-beam collimated fields were used to link the measurement results to a validated linear accelerator model. The quality of the mini-beam collimated field was clinically equivalent to that of the open field. Changes in the mini-beam collimated field in response to changes in both field size and collimator inclination were consistent across all three linear accelerators. However, PVDR, collimator factors, and relative output factors varied in excess of the measurement uncertainty, revealing a difference in the mini-beam collimated fields of each linear accelerator. The change in PVDR was proportional to that of the collimator factor and relative output factor. The Monte Carlo simulations showed that variation in the full-width half-maximum of the linear accelerators’ electron beam incident on the Bremsstrahlung target correlated to the variation in collimator factor and PVDR across the accelerators. These results demonstrate that while the mini-beam collimated field varies across linear accelerators, the effect can be accounted for in the linear accelerator model, allowing the planning and delivery of mini-beam collimated fields using medical linear accelerators.
Description
Keywords
Spatial Fractionation, Mini-Beam Radiation Therapy, Dosimetry, Monte Carlo
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics