Evaluation of Hyperarc Stereotactic Radiosurgery Planning for Base of Skull Lesions
Snyder K, Huang Y, Zhao B, Chetty I, Wen N, and Siddiqui S. Evaluation of Hyperarc Stereotactic Radiosurgery Planning for Base of Skull Lesions. J Med Phys 2019; 46(6):e627.
J Med Phys
Purpose: To compare the plan quality of HyperArc High Definition Radiotherapy (HDRT) plans to current templated SRS workflow for radiosurgery treatments of base-of-skull lesions. Methods: Ten base-of-skull intracranial patients (8 Acoustic Neuromas, 2 Cavernous Sinus) were re-planned using the HDRT workflow. The optimization objectives were the same as the templated workflow. The SRS normal tissue objective (NTO) was utilized in the HDRT plans whereas the manual NTO was utilized in the conventional SRS workflow. Base-of-skull lesions were chosen due to proximity to organs at risk such as the cochlea and the optic nerve. Dose to 95% (PTV-D95%) and maximum-point-dose (PTV-D0.035 cc) were evaluated for the PTV. Maximum- point-dose (OAR-D0.035 cc) of the proximal OAR (cochlea or optic nerve), the volume of normal brain that received 12 Gy (Brain-V12 Gy), and the maximum dose to the ipsilateral orbit (Orbit-Dmax) were evaluated. Conformity was compared using RTOG Conformity Index (CI), Paddick CI, Gradient Index (GI), and the total time for delivery was calculated from the monitor units (MUs). Statistical significance was evaluated using a paired student t-test. Results: No significant difference was found between the HDRT plan and the templated SRS plan for PTV-D0.035 cc, OAR-D0.035c, and Brain-V12 Gy. In the HDRT plans, PTV-D95% increased from an average of 13.0 Gy to 13.1 Gy (P = 0.006). The templated plans achieved better RTOG CI and GI, 1.14 vs 1.15 and 4.19 vs 4.23 respectively, than the HDRT plans; whereas the HDRT plans achieved better Paddick CI (0.83 vs 0.82), but were not statistically significant. MUs and subsequent calculated beam-on time were greater for the HDRT plans, on average 4.1 min vs 3.4 min for the templated SRS cases (P = 0.011). Conclusion: Plan quality between HDRT and templated SRS plans were similar. The increase in MUs and beam-on time suggest that the gain in efficiency from a HDRTworkflow may be due to delivery automation rather than planning.