Commissioning of Helium Ion Therapy and the First Patient Treatment With Active Beam Delivery.

PURPOSE: Helium ions offer intermediate physical and biological properties to the clinically used protons and carbon ions. This work presents the commissioning of the first clinical treatment planning system (TPS) for helium ion therapy with active beam delivery to prepare the first patients' treatment at the Heidelberg Ion-Beam Therapy Center (HIT). METHODS AND MATERIALS: Through collaboration between RaySearch Laboratories and HIT, absorbed and relative biological effectiveness (RBE)-weighted calculation methods were integrated for helium ion beam therapy with raster-scanned delivery in the TPS RayStation. At HIT, a modified microdosimetric kinetic biological model was chosen as reference biological model. TPS absorbed dose predictions were compared against measurements with several devices, using phantoms of different complexities, from homogeneous to heterogeneous anthropomorphic phantoms. RBE and RBE-weighted dose predictions of the TPS were verified against calculations with an independent RBE-weighted dose engine. The patient-specific quality assurance of the first treatment at HIT using helium ion beam with raster-scanned delivery is presented considering standard patient-specific measurements in a water phantom and 2 independent dose calculations with a Monte Carlo or an analytical-based engine. RESULTS: TPS predictions were consistent with dosimetric measurements and independent dose engines computations for absorbed and RBE-weighted doses. The mean difference between dose measurements to the TPS calculation was 0.2% for spread-out Bragg peaks in water. Verification of the first patient treatment TPS predictions against independent engines for both absorbed and RBE-weighted doses presents differences within 2% in the target and with a maximum deviation of 3.5% in the investigated critical regions of interest. CONCLUSIONS: Helium ion beam therapy has been successfully commissioned and introduced into clinical use. Through comprehensive validation of the absorbed and RBE-weighted dose predictions of the RayStation TPS, the first clinical TPS for helium ion therapy using raster-scanned delivery was employed to plan the first helium patient treatment at HIT.