Room: Exhibit Hall | Forum 7
Purpose: To analyze the distribution of normal brain volume receiving more than 12Gy (V12Gy) in multi-target Stereotactic Radiosurgery (SRS) plans treated using single-isocenter Volumetric Modulated Arc Therapy (VMAT). To investigate the feasibility of reducing variation in VMAT planning outcome based on previous planning knowledge.
Methods: 97 VMAT plans and 156 Dynamic Conformal Arc (DCA) plans for single-fraction intracranial SRS cases treated in 2017 at our institution were included in this analysis. VMAT was used for multi-target cases and DCA was for single-target cases; a total of 605 targets were treated with these plans. The prescription dose was normalized to 20Gy in all plans for this analysis. Normal brain V12Gy were calculated for each target and the distribution of V12Gy per target was plotted as a function of target volume for both VMAT and DCA plans. Targets in VMAT plans that had large deviation of V12Gy from average level were identified and the plans for these targets were re-optimized to determine the possibility of reducing variation of V12Gy in VMAT planning.
Results: The distribution of V12Gy exhibited larger variation in VMAT plans compared to DCA plans. 43 targets in VMAT plans were selected for re-planning, which resulted in re-optimization of 8 cases that had 2, 4 ,5, 7, 8, 9, 12, and 15 lesions, respectively. The mean reduction of V12Gy in the re-planned targets was 33.9% (range 10.5%-66.1%), while other dosimetric metrics including Conformity Index and target coverage were kept at the same level. After re-planning, the V12Gy distribution in VMAT plans more closely resembled that of DCA plans.
Conclusion: A distribution of normal brain V12Gy as a function of target size was established based on previous clinical cases. The results of re-planning showed that it is feasible to use this knowledge to guide VMAT planning and reduce high V12Gy outliers.