Monte Carlo-Based Treatment Planning and 3D Secondary Dose Check to Adjust PTV Coverage without Increasing OAR Dose for Conventional and Stereotactic Radiotherapy In Lung Cancer Patients
Abstract
Purpose
Monte Carlo (MC)-based treatment planning system (TPS; RayStation, RaySearch laboratories) and 3D secondary dose check software (VeriQA RT Montecarlo 3D, PTW) were commissioned and benchmarked against well-established TPS. This study investigates the dosimetric accuracy of Collapsed Cone (CC)-based clinical plans and compares them to MC optimized plans in a cohort of conventional and stereotactic lung cancer patients.
Methods
Water phantom measurements were used for commissioning of both RayStation and VeriQA. RayStation CC plans of 34 patients (breast, head-and-neck, prostate, bladder, kidney, anus, cervix, stereotactic lung, glioma and multiple brain metastases) were recalculated in VeriQA with MC dose-to-medium and dose-to-water (1% accuracy, grid size of the original plan). To investigate tissue heterogeneities effects, a cohort of 42 lung cancer patients was included: 10 treated with conventional radiotherapy (CRT) and 32 with stereotactic body radiotherapy (SBRT), all planned in RayStation v2023B. Adequate PTV coverage was defined as PTV-Vx>95%, with x=0.95Dpres (CRT) or 0.99Dpres (SBRT).
Results
Mean pass rates of secondary dose calculation in VeriQA for 34 patients were 99.2±1.7% for dose-to-medium and 99.0±1.2% for dose-to-water. For 42 lung patients, a significant reduction in PTV coverage was observed when recalculating clinical CC-based plans with the MC algorithm (p = 0.02). Average dose reductions not captured by CC were 12.3% (SBRT 3×18 Gy), 6.5% (SBRT 5×11 Gy), 4.6% (SBRT 8×7.5 Gy), and 6.7% (CRT 24×2.75 Gy). Optimization with MC significantly restored PTV coverage (p = 0.03) to levels comparable to the original CC-based plans, maintaining values above the 95% adequacy threshold. Non-significant variations were observed in OAR doses between CC-based and MC-optimized plans (p > 0.05).
Conclusion
Clinical CC-based plans inaccurately estimate PTV doses for lung cancer patients. MC-optimized plans restored PTV coverage without increasing OAR doses. Discrepancies between CC and MC calculations were more pronounced for SBRT than for CRT plans.