ESTRO 2024 - Abstract Book

S3309

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

The OSL film dosimeter is meant to be more accurate and reproducible than either its OSL or film counterparts. In this work we test the OSL film dosimeter’s different characteristics such as monitor unit (MU) linearity, dose rate dependence, etc. All tests performed were made in an effort to determine the dosimeter’s reproducibility, uniformity, and viability in the clinic.

Material/Methods:

A prototype BaFBr OSL film was cut into 6 even pieces and the pieces were irradiated on a Trilogy 21EX Varian linac and tested for different characteristics. The standard setup was 6 MV photon beam, with gantry and collimator at 0, 10 cm solid water phantom depth and roughly 1.5cm backscatter. The reader warmup time and fading were calculated, and a standard time was determined and used for the remainder of the tests.

Results:

Fading can contribute to 25% signal loss after an hour without scan. The reader should be on for more than an hour before irradiation to get a more consistent pixel value. Time between irradiation and readout was determined to be 10 minutes. This number was chosen to avoid needing to do fading correction equations. A consistent background pixel value of 5 is present in the film. Light sensitivity is so high a 90% signal loss was observed after 50 seconds in a room light, and a laser line was found on the image after a brief exposure to the lasers. Repeating the same measurement on the same film shows up to a 1% error in reproducibility. Dose rate is consistent at 1% variation up to 600 MU/min. There are no shown dependencies on gantry angle or energy. MU linearity was within 3.5% for every MU tested except the final point of 2000 MU. The sensitivity of the film varied depending on the section of film irradiated, leading to errors of up to 7% if not using the same piece of film.