Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir‐192 high dose rate brachytherapy

• Published in: Journal of applied clinical medical physics 2022-05, Vol.23 (5), p.e13571-n/a
• Main Authors: Huang, Lyu, Gaballa, Hani, Chang, Jenghwa
• Format: Article
• Language: English
• Subjects: Accuracy; Calibration; Dosimetry; EBT3 film; Energy; film calibration; HDR brachytherapy; Radiation Oncology Physics; Radiation therapy; radiochromic film dosimetry
• ISSN: 1526-9914; 1526-9914
• DOI: 10.1002/acm2.13571

Purpose To evaluate the dosimetric accuracy of EBT3 film calibrated with a 6 MV beam for high dose rate brachytherapy and propose a novel method for direct film calibration with an Ir‐192 source. Methods The 6 MV calibration was performed in water on a linear accelerator (linac). The Ir‐192 calibration was accomplished by irradiating the film wrapped around a cylinder applicator with an Ir‐192 source. All films were scanned 1‐day post‐irradiation to acquire calibration curves for all three (red, blue, and green) channels. The Ir‐192 calibration films were also used for single‐dose comparison. Moreover, an independent test film under a H.A.M. applicator was irradiated and the 2D dose distribution was obtained separately for each calibration using the red channel data. Gamma analysis and point‐by‐point profile comparison were performed to evaluate the performance of both calibrations. The uncertainty budget for each calibration system was analyzed. Results The red channel had the best performance for both calibration systems in the single‐dose comparison. We found a significant 4.89% difference from the reference for doses 600 cGy. Gamma analysis of the 2D dose distribution showed the Ir‐192 calibration had a higher passing rate of 91.9% for the 1 mm/2% criterion, compared to 83.5% for the 6 MV calibration. Most failing points were in the low‐dose region (