Simple and Reliable Calibration Fields for OrthoChromic Film Dosimetry Protocol
W Feng1*, C Shi2, J Zhou3, A Chu4, L Zhou1, J Sakellakis1, A Grann1, (1) Saint Barnabas Medical Center, Tenafly, NJ, (2) New York Proton Center, New York, NY, (3) Rutgers - Cancer Institute of New Jersey, New Brunswick, NJ, (4) Montefiore Medical Center, Stony Brook, NY
Presentations
PO-GePV-T-355 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To demonstrate various calibration fields for the newly introduced OrthoChromic Film Dosimetry Protocol to optimize dose accuracy in order to deliver stable film dosimetry results over a wide dose range.
Methods: The OrthoChromic OC-1 film was tested using Eclipse v15.6 with Truebeam and MultiPlan v5.3 with Cyberknife M6, respectively. The films were scanned in reflection mode on an Epson flatbed scanner with 48bit at 75dpi. A glass plate was used to flatten films on the scanner. OrthoChromic protocol requires a calibration film exposed to a calibration plan with multiple dose levels in scan direction and uniform dose in lateral direction, and a QA film exposed to patient specific QA plan. When the two films are scanned together in parallel in scan direction, the possible dose errors caused by lateral effect from scanner sensors and film coating variations are corrected. OrthoChrome Pro software was used to register films with corresponding plans, calculate delivered dose from film, and compare delivered dose to planed dose. Quality of QA film compared with planned dose were determined by gamma analysis at 2% and 2mm.
Results: (1) Truebeam jaw can generate a step wedge calibration field that provides reliable dosimetric results, with over 95% gamma passing rate.(2) Cyberknife MLC can generate calibration field comparable to the Truebeam 8-level step wedge, with over 95% gamma passing rate.(3) Using overlapping circular fields generated by Cyberknife Cone, an equally reliable calibration field can be generated, with over 95% gamma passing rate.(4) An actual patient treatment case QA was performed with the overlapping cone calibration. The reliability of this dosimtric method was confirmed with over 95% gamma passing rate.
Conclusion: There are many ways to design reliable calibration fields to obtain accurate dosimetric results using the newly introduced OrthoChromic Film Dosimetry Protocol.
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