This work explores how the choice of prescription isodose line (IDL) achieves a high probability of local tumor control (Tumor Control Probability, TCP) at low risk of normal tissue complications (Normal Tissue Complications Probability, NTCP) for Gamma Knife Radiosurgery at two different plans applying different isodose lines to evaluate the radiosurgical metrics, plan quality, and outcome probability in treatment of meningioma using Gamma Knife Radiosurgery (GKS).

METHODS: The cross-sectional study included 10 patients (4 male and 6 female) with median age of 42 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. A quantitative approach has been conducted to evaluate and compare both plans. Dose-volume histogram was imported to MATLAB to compute tumor control probability (TCP), normal tissue complications probability (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 5.44 cm3(0.59-23.72). TCP was significantly higher in the plan using 50% isodose line for the marginal dose than that using 75% isodose line (94.98%, 45.09%, p=0.0018, Mann-Whitney test). Brainstem and optic apparatus NTCPs were very low with median of 0.01% (0-0.03%) in the former plan and zero in the later one (p=0.005, Mann-Whitney test).

CONCLUSION: Radiobiological models and physical indices could be used for the optimum plan selection of GKS.