Multi-Detector in Vivo Dosimetry of Volumetric Arcs of Total Body Irradiation: An Institutional Comparative Study

Background: The purpose of this study was to evaluate the dosimetric difference in calculated and measured doses for volumetric modulated arc therapy enabled total body irradiation (VMAT-TBI) technique. The study also aims to find the uniformity of doses delivered at the junction region of two adjacent isocentric arcs using three different detectors. Material and Methods: This phantom study was performed on arc phantom and contains three different detectors: Gafchromic films, silicon diodes, and 0.6cc ionisation chamber. Measured doses using Gafchromic films and silicon diodes were the representative of skin surface doses and the 0.6cc chamber measured the mid plane doses at each isocenter. Ten (10) selected patients from the data base were the representative for this retrospective dosimetric analysis, verification and in-vivo dosimetry, however, the pre-treatment verification of all VMAT-TBI plans were already completed using EPIQA and Octavious phantom. Epson 1100 flatbed scanner was used for film scanning. The Gamma analysis and average dose difference between TPS calculated and measured with different dosimeters were found. Results: The found dose difference in surface doses measured using Gafchromic film is in the range from 0.044 to 0.204 cGy and for diodes the range is from 0 to 0.112 cGy with respect to planned values. The point doses at each arc isocenter were within 3% of TPS calculated. Conclusion: The diodes, gafchromic films and used ionisation chamber are in good agreement with the TPS doses. Hence, it can be concluded and suggested that any available detector is good for dose determination in TBI.