A Specific Patient Quality Assurance (PSQA) procedure for a Co-60 source based High Dose Rate Brachytherapy

Introduction: In radiation therapy, accurate dose determination and precise dose delivery to the tumor are directly associated with better treatment outcomes in terms of higher tumor control and lower post radiation therapy complications. The current study aims the development and clinical application of the Patient Specific Quality Assurance (PSQA) procedures for nasopharyngeal and Tongue cancer treated using a cobalt-60 based high-dose rate brachytherapy.   Materials and Methods: In this study, patient-specific quality assurance tools for brachytherapy in nasopharyngeal and Tongue cancers were utilized using a radiometric film dosimeter system through a gamma index for comparison. Also, with the association of dose distribution measured at surface area, and applying a reverse method, the calculated dose distribution at the region of interest were compared with those resulted from a treatment planning system. All results were also compared with those achieved by a Monte Carlo simulation classified as gold standard for the project. We also designed and evaluated two phantoms in this study. The first phantom designed based on the BALTAS phantom and the second one was created as a special phantom for brachytherapy applicators used for Nasopharyngeal and Tongue cancers. The same passing criteria used for external beam QA (3%/3mm), were applied. Finally, the PSQA system’s sensitivity to source positional errors was investigated by introducing intentional and controlled mistakes on selected patient’s plans.   Results: Results presented in this study demonstrated that radiochromic film dosimetry based PSQA for brachytherapy can be used not only for patient specific quality assurance, but also as a part of the commissioning process and periodic QA .   Conclusion: Patient Specific Quality Assurance tasks should be extended for all Radiotherapy tasks including Brachytherapy.