Patient-specific QA for moving target irradiation with a scanned ion beam in NIRS-HIMAC

Purpose: Three-dimensional (3D) pencil-beam scanning technique has been utilized since 2011 at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Beam delivery system and treatment planning software (TPS) require dosimetric patient-specific QA to check each individual plan. Any change in the scanned beams will result in a significant impact on the irradiation dose. In particular, in moving target irradiation with a scanned ion beam, the interplay effect between the target motion and scanned beams is a problem, because this effect cause over or under dosage in the target volume. Therefore, patient-specific QA for moving target irradiation requires additional procedure.Methods: In a conventional patient specific QA flow in NIRS-HIMAC, the planned dose distribution is converted to the dose distribution in the water phantom. After that, we perform the measurement and analysis. In the measurement, 2D ionization chamber with water column is used. In an additional QA for moving target irradiation, we placed 2D ionization chamber on the PMMA plate tilted with respect to the beam axis. The PMMA plate was set on the stage of the moving phantom. The moving phantom was moved according to patient data. We measured the dose distribution for both the static target and the moving target. We compared the results for the moving target with those for the static targets by means of a gamma index analysisResults: In the conventional patient-specific QA, the measured dose distributions agreed well with those calculated by the TPS, and the QA criteria were satisfied in all measurements. In the additional patient-specific QA, the gamma analysis between the moving and static targets showed the good agreement.Conclusions: We performed the additional patient-specific QA for moving target irradiation with a scanned ion beam. We confirmed that this new technique was a beneficial QA procedure for moving target irradiation.54th Annual Conference of the Particle Therapy Co-Operative Group (PTCOG54