Quality assurance procedures based on dosimetric, gamma analysis as a fast reliable tool for commissioning brachytherapy treatment planning systems
INTRODUCTION. Fast and easily repeatable methods for commissioning procedures for brachytherapy (BT) treatment planning systems (TPS) are needed. Radiochromic film dosimetry with Gamma analysis is widely used in external beam quality assurance (QA) procedures and planar film dosimetry is also increasingly used for verification of the dose distribution in BT applications. Using the Gamma analysis method for comparing calculated and measured dose data could be used for commissioning procedures of the newly developed TG-186 and MBDCA calculation algorithms. The aim of this study was dosimetric verification of the calculation algorithm used in TPS when the CT/MRI ring applicator is used.
METHODS AND MATERIALS . Ring applicators with 26 and 30 mm diameters and a 60 mm intra-uterine tube with 60º angle were used for verification. Gafchromic® EBT films were used as dosimetric media. Dose grids, corresponding to each plane (dosimetric film location), were exported from the TPS as a raw data. Gafchromic® films were digitized after irradiation. Gamma analysis of the data were performed using the OMNI Pro I’mRT® system, as recommended by the AAPM TG-119 rapport criterion for gamma analysis of 3%, 3mm and a level of 95%.
RESULTS: For the 26 mm and 30 mm rings, the average gamma ranged, respectively, from 0.1 to 0.44 and from 0.1 to 0.27. In both cases, 99% of the measured points corresponded with the calculated data.
CONCLUSIONS. This analysis showed excellent agreement between the dose distribution calculated with the TPS and the doses measured by Gafchromic films. This finding confirms the viability of using film dosimetry in BT.
Keywords: brachytherapy, quality assurance, film dosimetry, ring applicator