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Evaluation of the Dose-Rate Dependency of GAFCHROMIC EBT3

G Twork

G Twork*, A Sarfehnia, McGill University Health Centre, Montreal, QC

SU-E-T-88 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the effect of different dose rates on the optical density (OD) for the commercially available GAFCHROMIC EBT3 film using a Novalis TX.

Methods: 3x3 cm² pieces of GAFCHROMIC EBT3 (A12141101) were placed on the surface of a 20x20x20 cm³ solid water phantom. A 2 cm thick block of solid water was placed on the film for build-up. The machine output was monitored using a Farmer-type chamber located at a depth of 10 cm below the films. Chamber ion recombination as a function of dose rate was accounted for, and pressure and temperature were monitored throughout. The monitor unites were calculated such that a certain dose (50, 100, 500 cGy) was delivered at the level of the film. The dose rate was varied between 50 and 1000 cGy/min through changing both machine settings (100-600 MU/min, 1000 MU/min in SRS mode and source-to-surface distance SSD (75-135 cm). The films were scanned 24 hours post irradiation, and the resulting changes in net OD were compared against the corresponding dose rate.

Results: Preliminary examination of net OD results shows a small dependence on dose rate, but within the uncertainty of the measurements. As such, within the uncertainties of clinical film dosimetry, the GAFCHROMIC EBT3 films are independent of dose rate (50-1000 cGy/min) irrespective of the total delivered dose (between 50-500 cGy).

Conclusion: Results suggest GAFCHROMIC EBT3 films to be dose rate independent to within 3% for a wide range of dose rates (and total delivered doses) that are normally used in clinical settings.

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