Author: Milad BaradaranGhahfarokhi, Manuel A. Morales Paliza 👨🔬
Affiliation: Vanderbilt University Medical Center 🌍
Purpose: The purpose of this study was to commission Varian HDR surface applicators using a high-resolution diode array and film dosimetry. This work evaluates dosimetric characteristics of these applicators to improve accuracy and precision in calibration and treatment setup.
Methods: Distributions of lateral profiles were measured using SRS MapCHEK (Sun Nuclear, Melbourne, FL) and EBT3 films (Ashland, NJ). DoseLab Pro software (Varian Medical Systems, Palo Alto, CA) was used to read all films after the irradiations. Measurements were compared with calculations of BrachyVision (Varian Medical Systems, Palo Alto, CA) using both TG-43 and Acuros XB algorithms.
Results: The measured Full Width at Half Maximum (FWHM) data with different detectors had an overall agreement (< 3.2 mm) with applicator nominal sizes. Average agreement of < ± 1.6 mm was found for different applicator sizes. SRS MapCheck showed higher discrepancies than film, especially for 25 mm applicator (up to 4.0 mm), when the FWHMs were compared with Acuros XB calculations. Gamma evaluations of the SRS MapCheck profiles were in good agreement (> 84.7% pass rate for 3%/3 mm criteria) with Acuros XB calculations, except for the 25 mm applicator (73.6% pass rate for 3%/3 mm criteria). Gamma evaluations of the film dosimetry profiles were in agreement (> 82.1% pass rate for 3%/3 mm criteria) with Acuros XB calculations for all the applicator sizes.
Conclusion: EBT3 film is recommended for a reliable and efficient lateral and FWHM dose verification for commissioning of Varian HDR surface applicators. This work indicates the potential to streamline the HDR brachytherapy surface cone commissioning process using the SRS MapCHECK, although some discrepancies might be found mainly due to detector spacing.