SU-E-T-176: Commissiong and Initial Clinical Experience with Dosimetry Check, a Commercial Software for in Vivo Volumetric Dosimetry

Purpose: The aim of this work is to study the differences of reference point doses between the commercial EPID based dosimetry software Dosimetry Check (DC) and TPS to establish an accuracy level of the system, to evaluate its use in clinical routine and to obtain results for the first patients. Methods: We used DC v.3.8 (Math Resolutions), two Varian Clinac iX accelerators equipped with EPID aS1000 and Eclipse v.10.0 with AAA algorithm. Several plans with and without air gap were generated over the phantoms: MP1 Water Tank and Solid Octavius 4D (PTW). 5 head and neck, 3 lung and 4 prostate cases were selected for clinical evaluation. We compared the calculated dose at the isocenter and in a set of 9 points distributed in the PTV and made a gamma analysis of the 3D volume in pre‐treatment mode and during 3 CBCT‐guided sessions in transit mode. Results: In the study with phantoms, total dose differences in the isocenter between DC and TPS are less than 2%, but single field contributions achieve greater values. In transit mode, DC does not consider properly the couch attenuation, especially when there is an air gap between phantom and couch. For patients, better results are observed for prostate than for lung (heterogeneities) or head and neck (heterogeneities, field size). Information is lost in edges of large fields due to the limitation in EPID size and in the event of an interruption during treatment. Conclusion: Tests carried out with phantoms suggest that the accuracy of DC achieves 2% for total dose. For off‐axis dose distribution, and also for patients, this uncertainty results significantly higher. In any case, the possibility of this in vivo evaluation and the potentiality of this new system have a very positive impact on improving patient QA.