Study of X-ray field junction dose using an a-Si electronic portal imaging device.
Field junctions between megavoltage photon beams are important in modern radiotherapy for treatments such as head and neck and breast cancer. An electronic portal imaging device (EPID) may be used to study junction dose between two megavoltage X-ray fields. In this study, the junction dose was used to determine machine characteristics such as jaw positions and their reproducibility, collimator rotation and the effect of gantry rotation. All measurements were done on Varian linear accelerators with EPID (Varian, Palo Alto, CA). The results show reproducibility in jaw positions of approximately 0.3 mm for repeated jaw placement while EPID readings were reproducible within a standard deviation of 0.4% for fixed jaw positions. Junction dose also allowed collimator rotation error of 0.1 degrees to be observed. Dependence of junction dose on gantry rotation due to gravity was observed; the gravity effect being maximum at 180 degrees gantry angle (beam pointing up). EPIDs were found to be reliable tools for checking field junctions, which in turn may be used to check jaw reproducibility and collimator rotation of linacs.
Department of Physical Sciences, Peter MacCallum Cancer Centre, Locked Bag 1 A'Beckett Street, Melbourne, VIC 8006, Australia. mebratu.madebo@petermac.org
Mebratu
M
Madebo
A
A
Perkins
C
C
Fox
P
P
Johnston
T
T
Kron
D004581:Electronics / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D011829:Radiation Dosage; D011874:Radiometry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012825:Silicon; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*; D014963:X-Ray Intensifying Screens
D012825:Silicon