Room: AAPM ePoster Library
Purpose: To develop a versatile interface for a commercial treatment planning system (TPS) to enable Monte Carlo (MC) dose calculations of intensity modulated proton therapy (IMPT) plans and to compare the resulting MC dose distributions of spot scanning proton plans to analytical TPS calculations.
Methods: An in-house framework for MC treatment planning is extended with an interface to perform MC dose re-calculation of spot scanning proton plans generated in the Eclipse TPS (Varian Medical Systems). These dose calculations, using proton Macro MC (pMMC), can be performed on a local workstation or parallelized on a high-performance cluster and allow for different user defined calculation options. A three field IMPT plan for a clinically motivated head and neck case calculated with the TPS is compared to the MC re-calculation, for both homogeneous and inhomogeneous situations by means of dose differences and dosimetric parameters.
Results: For the homogeneous water equivalent scenario, the dosimetric parameters of the TPS and the MC re-calculated IMPT plan are equivalent. For the case with tissue inhomogeneities, the TPS plan degrades upon MC re-calculation (PTV homogeneity 99.6% vs. 94.4%). Local dose differences of up to -20% are observed in the normal tissue.
Conclusion: The new interface enables an automated and flexible setup of MC re-calculation of Eclipse TPS spot scanning proton plans. For homogeneous situations, there is no substantial difference between TPS and MC dose calculations. For inhomogeneous situations, MC based dose calculation show substantial differences to the analytical TPS calculation.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Varian Medical Systems.