Machine and Patient-Specifc Quality Assurance Procedures for Intensity Modulation Proton Therapy

In July 2008, the Chang Gung Memorial Hospital (CGMH) signed a contract with Sumitomo Heavy Industry, Japan to start the project of building the first proton therapy facility in Taiwan. The proposed beam delivery methods for gantries G3 and G4 of the CGMH system adopt a unique dynamic scanning technique through control of its scanning speed. Up to date, the proton therapy community has not yet reached consensus of what quality assurance (QA) procedures are optimal for dynamic scanning systems, probably because these systems are relatively new and technically variant among different centers. This study does not intend to take over the routine QA operation. Instead, it tries to develop special procedures for (a) machine QA of the new IMPT delivery method and (b) new patient-specific QA for IMPT patient treatments. Breakdown analysis of the dynamic scanning method suggests that four machine parameters must be checked for a complete machine QA protocol: pristine BP (D(Ej,di)), beam current (I), scanning speed (v) and spot size (0). In addition, it also suggests that a scanning pattern designed to verify machine performance should be developed to check beam characteristics including (a) spot dependence on energy, (b) spot dependence on lateral beam position, (c) MU control, (d) stability of beam current control, (e) speed control, and (f) penetration depth control. Combination of 2-D ion chamber array measurement and an in-house beam characteristic analysis software program are proposed by the study for IMPT machine QA. For IMPT patient-specific QA procedures, our group proposed a hybrid method of combining in-air intensity distribution measurements and an analytical dose calculation algorithm in hope to reduce the amount of required measurements. The analytical dose calculation algorithm is based on the method of Hong. This method can verify both the treatment planning calculation and beam delivery at the same time.

Project ID:PC10301-0542
External Project ID:NSC102-2314-B182-059-MY2