Plan Score Index (PSI): A Tool for Comprehensive Comparative Evaluation of Gamma Knife Treatment Plans

'Plan Score Index (PSI)' has been formulated for GKRS treatment plans that will evaluate the best plan out of two or more than two plans in terms of conformity index (CI), gradient index (GI), coverage, selectivity, number of shots (NOS), and total treatment time (TT).

To validate PSI, already treated 54 patients of Gamma Knife Perfexion were retrospectively planned and evaluated. These 54 patients had already been treated with the ideal plan and replanned retrospectively for evaluation of the plans. Two different plans i.e. forward (FP) and inverse hybrid plan (IHP) were created by medical physicist using Leksell GammaPlan® (version10.1.1). The plans were evaluated on the PSI value.

The mean PSI value for FP and IHP is 0.80±0.66 and 1.38±1.44 respectively. IHP generated plans with higher PSI values because of lesser number of shots and treatment time. The mean PSI difference between both of them is -0.95 showing the superiority of IHP technique (p= 0.00004).

Plans with higher PSI are better in terms of stereotactic treatment and dosimetric parameters. PSI is a valuable adjunct for comparative evaluation of competitive plans for a single patient.