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SU‐G‐BRB‐06: Commissioning and Evaluation of EPID‐Based in Vivo Dosimetry Software Using a Tissue‐Maximum Ratio Approach
Author(s) -
Held M,
Cheung J,
Husson F,
Morin O
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956913
Subject(s) - isocenter , truebeam , dosimetry , nuclear medicine , dose profile , radiation treatment planning , monitor unit , image guided radiation therapy , beam (structure) , computer science , medical physics , physics , medicine , medical imaging , optics , linear particle accelerator , radiation therapy , imaging phantom , radiology , artificial intelligence
Purpose: To commission and evaluate an in vivo EPID‐based transit dosimetry software (EPIgray, DOSIsoft, Cachan, France) using simple fields and TG119‐based IMRT treatment plans. Methods: EPIgray was commissioned on a Truebeam based on finite tissue‐maximum ratio (fTMR) measurements with solid water blocks of thicknesses between 0 and 37 cm. Field sizes varied from 2×2 to 20×20 cm 2 . Subsequently, treatment plans of single and opposed beams with field sizes between 4×4 and 15×15 cm 2 as well as IMRT plans were measured to evaluate the dose reconstruction accuracy. Single field dose predictions were made for anterior‐posterior and lateral beams. IMRT plans were created based on TG119 recommendations. The reconstructed dose was compared to the planned dose for selected points at isocenter and away from isocenter. Results: For single square fields, the dose in EPIgray was reconstructed within 3% accuracy at isocenter relative to the planned dose. Similarly, the relative deviation of the total dose was accurately reconstructed within 3% for all IMRT plans with points placed inside a high dose region near the isocenter. Predictions became less accurate than 5% when the evaluation point was outside the majority of IMRT beam segments. Additionally, points 5 cm or more away from the isocenter or within an avoidance structure were predicted less reliably. Conclusion: EPIgray formalism accuracy is adequate for an efficient error detection system. It provides immediate intra‐fractional feedback on the delivery of treatment plans without affecting the treatment beam. Besides the EPID, no additional hardware is required, which makes it accessible to all clinics. The software evaluates point dose measurements to verify treatment plan delivery and patient positioning within 5% accuracy, depending on the placement of evaluation points. EPIgray is not intended to replace patient‐specific quality assurance but should be utilized as an additional layer of safety for continuous patient treatment verification. This research is supported by DOSIsoft.