Beam commissioning of a new compact scanned proton therapy system with four different dose calculation algorithms

The Central Japan International Medical Center (Gifu prefecture, Japan) as the 20th Proton Therapy Institution in Japan, has newly installed a compact scanned proton therapy system, ProBeam 360°™. We installed two commercial treatment planning systems (TPSs): Eclipse and RayStation. No commissioning results have been reported between Varian's newest compact proton therapy system and the two TPSs.​ PURPOSE: We identified the optimal dose calculation algorithm for clinical use by evaluating the dose agreements between four dose calculation algorithms provided by two TPSs and the measured values using our new machine.

The two TPSs each had a pencil beam algorithm (PBA) and Monte Carlo (MC) dose engines (four in total). Validation plans were created for 26 box targets (with and without a 50-mm range shifter) in a homogeneous phantom optimized using Eclipse. We created three realistic clinical plans consisting of 42 beams in mock patients with prostate, head and neck, and C-shaped targets. We validated 12 heterogeneous plans for the lung and bone regions using all three optimizations and four dose algorithms with the TPSs. Measurements were performed on the lateral profiles at the isocenter plane. The calculated doses for each algorithm were compared with the measured doses.

Each dose algorithm achieved an average gamma score of at least 95.6 ± 5.0% or higher (RayStation PBA) at 3%/3 mm in the box plans. For the patient and heterogeneous plans, the average gamma score exceeded 95% for only two MC algorithms. RayStation MC showed the highest dose calculation accuracy in both homogeneous and heterogeneous regions.

All calculated doses of the box plans were in good agreement with the measurements, except for the RayStation PBA. For clinical use, RayStation MC is the preferred option for both homogeneous and heterogeneous cases.