SU‐E‐T‐52: Independent Dose Verification System for Spot Scanning Proton Therapy

Purpose: Similar to IMRT, patient specific quality assurance (QA) is an essential part of intensity modulated proton therapy (IMPT). Patient‐specific QA based on measurements only is a time‐consuming process. In this work, we developed and validated an independent dose verification system which will be used as a part of the patient specific QA process to improve the QA efficiency for IMPT patients. Methods: A recently developed pencil beam algorithm base on measured in‐water single‐spot profiles was implemented. The algorithm added a modified Cauchy‐Lorentz function to accurately model individual scanning spot. For the purpose of independent dose calculation, it is sufficiently different from the in‐air fluence‐based algorithm of our clinical treatment planning system (TPS). QA tasks can be seamlessly communicated between TPS and the verification system through DICOM network streams. Verification results were generated without human intervention and analyzed using data extracting and analyzing tools. Patient specific measured data of ten patients were selected to validate the system, among which five were treated with single‐field optimization (SFO), and five with multiple‐field optimization (MFO). The measured and calculated dose distributions were compared at points, and 2D planes at various depths. Results: AT least 98% of dose pixels passed 2% relative dose/2 mm distance to agreement (DTA) gamma criteria for all 2D dose planes of SFO cases. At least 95% of dose pixels passed the same gamma criteria for all MFO cases. Calculated values are within 3% or 2 mm DTA of measurements for 97% of validated point doses. Conclusions: We havedeveloped and validated an independent dose verification system for IMPT. The proposed system may reduce the amount of measurement and beam time required for patient specific QA processes, while maintaining a reasonable confidence to deliver a treatment safely and effectively.