Room: Exhibit Hall
Purpose: BNCT-30 is a commercially available cyclotron-based boron neutron capture therapy (BNCT) system equipped with beryllium target. This work aims to present our institutional experience-based methodology of commissioning and quality assurance and its optimization for dosimetry of BNCT-30 irradiation field.
Methods: Based on the dosimetric QA items summarized in AAPM TG-142, the dosimetric QA requirements for clinical use of commercial BNCT system were reviewed and rearranged for each dosimetric component such as thermal/epithermal/fast neutrons and gamma-ray constituting the irradiation field.
Results: From the results of tumor dose simulation by MCNPX and acceptance test, collimator surface (Ref0â€™), phantom surface (Ref0), 2-cm and 6-cm depth in phantom (Ref1 and Ref2) were determined as reference depths for measurement of daily, monthly, and annual QA. Each QA procedure consisted of measurements of thermal/epithermal and fast neutron fluence by gold and indium reaction rate, and gamma ray measured by thermoluminescence dosimeter, avoiding the use of real-time neutron detectors because of its unclear durability. However, the measurement of fast neutron fluence with indium foils was limited only to annual QA procedures in view of a high volume of the work despite small contribution to RBE dose. Due to intricacy of the evaluation for all components, daily beam output constancy test was limited to the evaluation for the dominantly contributed thermal neutron at Ref0â€™ with Au activation rate using smaller charge amount. Alternatively, thermal neutron and gamma ray measurement were added as weekly QA. Monthly QA included beam quality profile constancy test, and annual QA included a beam symmetry constancy test, output calibration of proton charge monitor, and evaluation of linearity between charge monitor value and each component dose.
Conclusion: This methodology provides an easy and reliable QA method that can be clinically applied with dosimetric validity for the mixed irradiation field of BNCT.