Commissioning Valencia Applicators Using Film Dosimetry In Solid Phantom
Abstract
Purpose
Within the range 100 keV to 15 MeV and dose higher than 500cGy, GafChromic EBT3 films exhibits very weak energy dependent. However, EBT3 films are no longer produced. In this study, EBT4 GafChromic films were used for absolute dose measurement on HDR flexitron source – Ir-192.
Methods
Films have been irradiated at increasing known doses with 6 MV beams and the calibration curve is built up for film analysis. The EBT4 films were used to measure the doses at the depth of 3 mm using Valencia applicators with the two different diameters (3 cm vs. 2 cm). Matlab codes were developed for film analysis and dealing with RT dose in DICOM format. The setup of the dose measurement is described as follows: Films with 7 cm x 6 cm were placed in the solid phantom beneath Valencia applicator. Only one dwell position in Valencia applicator was used in Oncentra treatment planning and the sweet spot was first calibrated and then used for irradiating the films of the planned dose of 1000 cGy at the depth of 3 mm.
Results
The film dosimetry showed that the doses on the films in the depth of 3 mm were 978.5 cGy with 3 cm diameter applicator and 992.3 cGy with 2 cm diameter applicator along the central axis as showed in Supporting Material. Compared to the planned dose of 1000 cGy in two different applicators with the diameters 2cm and 3cm, repectively, the difference is -2.92% lower and -0.77% lower, respectively.
Conclusion
A film dosimetry on Flexitron source - Ir192 was developed for absolute dose measurement, which can be improved by calibrating the films with about the same energy as Flexitron source - Ir-192.