Room: Davidson Ballroom A
Purpose: To quantitatively compare Stereotactic Radiosurgery (SRS) treatment plan quality between single isocenter, linac-based and gamma stereotactic unit delivery for a representative set of multi-target clinical presentations.
Methods: Five complex clinical cases with multiple brain metastases that reflect the heterogeneity of clinical scenarios encountered at our institution were chosen for evaluation. A Gamma Knife plan (GammaPlan v10.1.1, Elekta, Crawley, UK) and single-isocenter linac-based plan (HyperArc (HDMLC) Eclipse v15.5, Varian Medical Systems, Palo Alto, CA) were created for each case. Plans were normalized to deliver the prescription dose to >99% of each target volume with prescription doses ranging between 15-20Gy per lesion based on size and proximity to sensitive organs at risk (OAR). Plans were evaluated using common SRS indices including RTOG Conformity Index (CI), Paddick Gradient Index (PGI), and normal brain volume receiving 12Gy (V12Gy). Plan CI and PGI values are averages over all targets. Generalized Equivalent Uniform Dose (gEUD) for normal brain (a=4.5) was also evaluated.
Results: Both platforms produced clinically acceptable plans for all cases based on target coverage and OAR dose constraints. HyperArc (HA) provided superior CI, gEUD, and V12Gy for all cases while Gamma Knife (GK) provided superior PGI for 4/5 cases. HA provided a 22% improvement in mean CI (1.3 vs 1.6) and 44% reduction in mean V12Gy (10.1cc vs 15.9cc). GK provided a 17% improvement in mean PGI (3.8 vs 4.5). Mean and maximum target doses were, on average, 15% and 35% higher for GK, respectively.
Conclusion: For a representative set of multi-target SRS cases, HyperArc is capable of creating single-isocenter HDMLC plans that rival Gamma Knife in terms of both conventional SRS metrics and normal brain gEUD. Target conformity and normal brain V12Gy and gEUD were superior for HA, while PGI, and target mean and maximum dose were superior for GK.