Premium
SU‐E‐T‐118: Dose Verification for Accuboost Applicators Using TLD, Ion Chamber and Gafchromic Film Measurements
Author(s) -
Chisela W,
Yao R,
Dorbu G
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888448
Subject(s) - materials science , thermoluminescent dosimeter , imaging phantom , ionization chamber , dosimetry , calibration , dose profile , thermoluminescent dosimetry , nuclear medicine , optics , physics , ion , dosimeter , medicine , quantum mechanics , ionization
Purpose: To verify dose delivered with HDR Accuboost applicators using TLD, ion chamber and Gafchromic film measurements and to examine applicator leakage. Methods: A microSelectron HDR unit was used to deliver a dose of 50cGy to the mid‐plane of a 62mm thick solid water phantom using dwell times from Monte Carlo pre‐calculated nomograms for a 60mm, 70mm Round and 60mm Skin‐Dose Optimized (SDO) applicators respectively. GafChromic EBT3+ film was embedded in the phantom midplane horizontally to measure dose distribution. Absolute dose was also measured with TLDs and an ADCL calibrated parallel‐plate ion chamber placed in the film plane at field center for each applicator. The film was calibrated using 6MV x‐ray beam. TLDs were calibrated in a Cs‐137 source at UW‐Madison calibration laboratory. Radiation leakage through the tungsten alloy shell was measured with a film wrapped around outside surface of a 60mm Round applicator. Results: Measured maximum doses at field center are consistently lower than predicated by 5.8% for TLD, 8.8% for ion chamber, and 2.6% for EBT3+ film on average, with measurement uncertainties of 2.2%, 0.3%, and 2.9% for TLD, chamber, film respectively. The total standard uncertainties for ion chamber and Gafchromic film measurement are 4.9% and 4.6% respectively[1]. The area defined by the applicator aperture was covered by 80% of maximum dose for 62mm compression thickness. When 100cGy is delivered to mid‐plane with a 60mm Round applicator, surface dose ranges from 60cGy to a maximum of 145cGy, which occurs at source entrance to the applicator. Conclusion: Measured doses by all three techniques are consistently lower than predicted in our measurements. For a compression thickness of 62 mm, the field size defined by the applicator is only covered by 80% of prescribed dose. Radiation leakage of up to 145cGy was found at the source entrance of applicators.