Validation of the Raystation Treatment Planning System for IMRT Treatment on the 0.5 T Biplanar Linac-MR Hybrid (Aurora-RT)
Abstract
Purpose
To validate the treatment planning system (TPS), RayStation 11B, for IMRT treatment deliveries on the 0.5 T Biplanar Linac-MR (Aurora-RT)
Methods
RayStation 11B (Collapsed Cone Algorithm) has previously been commissioned for 3D-CRT treatment on the Linac-MR. MLC parameters in the TPS (leaf transmission, leaf offset, tongue and groove) are optimized by using an established formalism requiring a series of symmetric and asymmetric sweeping gap measurements and MLC open/closed measurements. Leaf tip width is not modeled due to the non-rounded MLC leaf tip design. Magnetic field effects are not explicitly modeled. Step and Shoot IMRT plans are generated in TPS based on standard TG119 requirements and constraints. Additionally, 8 mock prostate plans (5-field IMRT)) are generated based on PROFIT dose constraints. Patient prostate plans are assessed by a radiation oncologist. PSQA plans for TG119 and patient plans are recalculated and delivered on the Octavius 1500 MR phantom.
Results
All planning constraints are met for TG119 plans except for the “hard” C-Shape plan. For PSQA evaluation, TG-119 plans yield gamma pass rate of 99.4/97.2% (mean/min) at 3%/3mm, and a gamma pass rate of 97.8/93.4% (mean/min) at 2%/2mm. The lowest rates are Head & Neck and Multi Target plan. 8 mock prostate treatments are generated using the 5 field IMRT technique based on the PROFIT protocol, meeting dose constraints and deemed clinically acceptable by the radiation oncologist. PSQA for the 5 field prostate plans yields pass rates of 99.9/98.6% (mean/min) at 2%/2mm.
Conclusion
The current Linac-MR MLC design is adequately modeled in RayStation 11B for accurate step and shoot IMRT TG-119 plans. For our 8 mock prostate patients, clinically acceptable 5 field plans are generated in the RayStation 11B treatment planning system, with an excellent PSQA pass rate of 99.9/98.6% (mean/min) at 2%/2mm, despite not explicitly modeling for magnetic field effects.