Quality of Radiosurgical Plans by Leksell Gamma Knife Perfexion in the Treatment of Meningioma: Comparison between two isodose lines (50% and 75%)

Introduction: Radiosurgery is a well-established available technique for treating many diseases and indications. Planning quality assessment is a crucial step in the procedure itself and outcome probabilities; either control or complication probability. Several physical indices and methodology have been developed to describe any plan. Accordingly, plan quality and outcome could be compared with other plans. In current study, the aim was to compare two plans with different isodose line using radiobiological model, tumor control probability (TCP), normal tissue complication probability (NTCP) and plan’s physical indices. Material and Methods: The cross-sectional study included 20 patients (5 male and 15 female) with median age of 44 years (21-66) and presented with radiologically diagnosed meningioma. Two radiosurgical forward plans were applied with same marginal dose of 12Gy at two different isodose lines of 50% and 75% isodose alternatively using Leksell Gamma Plan of single session GKS. Dose-Volume Histogram (DVH) was imported to MATLAB to compute TCP, NTCP values at 5 years for each plan, and physical indices such as coverage, selectivity, conformity, heterogeneity, and gradient indices. Results: Median target irradiated volume was 7.5 cm³ (0.588 -23.72). TCP was significantly higher in the plan using 50% isodose line for the marginal dose than that using 75% isodose line (95.05%, 49.44%, p 0.05, Independent Samples t-Test). Brainstem and optic apparatus NTCPs were very low 0.01% (0-0.045%) in the former plan and zero in the later one (p =0.001, Mann-Whitney test). Conclusion: Radiobiological models and physical indices could be used for the optimum plan selection of GKS.