A comparison of two pencil beam scanning treatment planning systems for proton therapy

Objective: Analytical dose calculation algorithms for Eclipse and Raystation treatment planning systems (TPS), as well as a Raystation Monte Carlo model are compared to corresponding measured point doses. Method: The TPS were modeled with the same beam data acquired during commissioning. Thirty-five typical plans were made with each planning system, 31 without range shifter and four with a 5 cm range shifter. Point doses in these planes were compared to measured doses. Results: The mean percentage difference for all plans between Raystation and Eclipse were 1.51 +/- 1.99%. The mean percentage difference for all plans between TPS models and measured values are -2.06 +/- 1.48% for Raystation pencil beam (PB), -0.59 +/- 1.71% for Eclipse and -1.69 +/- 1.11% for Raystation monte carlo (MC). The distribution for the patient plans were similar for Eclipse and Raystation MC with a P-value of 0.59 for a two tailed unpaired t-test and significantly different from the Raystation PB model with P = 0.0013 between Raystation MC and PB. All three models faired markedly better if plans with a 5 cm range shifter were ignored. Plan comparisons with a 5 cm range shifter give differences between Raystation and Eclipse of 3.77 +/- 1.82%. The mean percentage difference for 5 cm range shifter plans between TPS models and measured values are -3.89 +/- 2.79% for Raystation PB, -0.25 +/- 3.85% for Eclipse and 1.55 +/- 1.95% for Raystation MC. Conclusion: Both Eclipse and Raystation PB TPS are not always accurate within +/- 3% for a 5 cm range shifters or for small targets. This was improved with the Raystation MC model. The point dose calculations of Eclipse, Raystation PB, and Raystation MC compare within +/- 3% to measured doses for the other scenarios tested.