Small field dosimetry: Chamber selection and its validation using technical report series-483

Objectives: Small field dosimetry plays a critical role in modern radiotherapy techniques such as IMRT, IGRT, VMAT, SRS, SRT, SBRT, and Tomotherapy, where the goal is to deliver a highly conformal dose to the tumour while minimizing exposure to surrounding healthy tissues. Accurate dosimetric measurements are essential to ensure treatment efficacy and patient safety. While TRS-398 serves as the Code of Practice (CoP) for dosimetry in conventional large field radiotherapy. The objective of the study was to evaluate the performance of these detectors and identify the most suitable one by comparing the measured output factors with reference data. Material and Methods: In this study, various detectors available in our department were employed to measure output factors for different small field sizes. The measurements were performed according to TRS-483 guidelines, and the obtained output factors were compared against reference data from standardized studies. Results: Differences in measured output factors were observed among the detectors, particularly in the smallest field sizes. From the comparison keeping Gafchromic film data as the standard it was seen that CC01 is more suitable for 6 MV-FF beam measurement whereas EPD gives least percentage deviation for the output factors of 6 MV-FFF beams. Conclusion: The results emphasize the importance of choosing an appropriate detector for small field measurements and adhering to TRS-483 recommendations to ensure accurate and reliable dosimetry in advanced radiotherapy applications.