Dosimetric comparison of single and double collimator stereotactic body radiotherapy plans using Cyber Knife for carcinoma prostate

Purpose: This study was conducted to evaluate single collimator (SC) and double collimator (DC) plans with respect to dosimetric analysis, calculated dose delivery to OAR and treatment time in carcinoma prostate patients treated with cyberknife. Materials and Methods: A retrospective study was conducted among twenty low and intermediate risk carcinoma prostate previously treated with Cyberknife. PTV was created and OARs were delineated. The prescribed dose was set as 37.5 Gy in 5 fractions and a base plan (BP), followed by three reduction plans (time, beam and node) were generated for both single and double collimators with sequential optimization module. The SC and DC plans were compared for the above-said variables. The mean differences were compared using paired t-test. A p-value of <0.05 was taken as statistically significant. Results: The median age of the patients was 63 years. DC plans had tighter isodose lines. The means of minimum doses did not vary significantly across the plans but the mean and maximum doses, PTV D2 and V95 means were significantly higher in single collimator plan. The mean CI and HI values were better in DC plans. The doses to OAR were comparable in both single and double collimator plans in terms of maximum doses. The mean doses received by OAR’s were significantly lesser in DC plans.SC plans resulted in lesser beams, nodes, MU and treatment time. Conclusion: Double collimator plans were better in producing good dosimetric results and reduced OAR doses with lesser estimated treatment efficiency.