S1910
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
used for their computational efficiency, they may inaccurately estimate dose in low-density regions and at bone-tissue interfaces, potentially compromising PTV coverage. This study investigates the dosimetric accuracy of CC-based clinical plans and compares them with ground truth Monte Carlo (MC) optimized plans in a cohort of conventional and stereotactic lung cancer patients. Material/Methods: A cohort of 42 lung cancer patients was included: 10/42 treated with conventional radiotherapy (CRT) and 32/42 with stereotactic body radiotherapy (SBRT), all planned in RayStation v2023B. Prescription doses were 64 Gy in 24 fractions (10/42) for CRT and 54 Gy in 3 (10/42), 60 Gy in 8 (10/42), or 55 Gy in 11 fractions (12/42) for SBRT, depending on tumour location1,2. Adequate PTV coverage was defined as PTV-Vx>95%, with x=0.95Dpres (CRT) or 0.99Dpres (SBRT). For each patient, three plans were created and evaluated: (i) a CC-based clinical treatment plan (Initial CC), (ii) an MC- based plan recalculated from the clinical plan (Initial MC), and (iii) an MC-optimized plan (New MC) designed to achieve similar OAR doses as the Initial CC plan. Treatment plans were compared in terms of adequate PTV coverage and OAR doses. Results: All relevant DVH comparisons are summarized in Table I. For all patients, a significant reduction in PTV coverage was observed when recalculating the clinical CC-based plans with the MC algorithm (p=0.02). Average dose reductions not captured by CC were 12.3%-points (SBRT 3 × 18 Gy), 6.5%-points (SBRT 5 × 11 Gy), 4.6%-points (SBRT 8 × 7.5 Gy), and 6.7%-points (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 New MC plans (p>0.05). For SBRT patients, the Dmean of Lung-GTV increased by 0.2 Gy on average, while D0.03cc for the Bronchus decreased by 0.5 Gy. For CRT patients, Dmean dose increases of 0.7 Gy and 0.2 Gy were found for the Lung-GTV and Heart, respectively.
Conclusion: Accurate lung RT requires MC optimization, especially for high-dose stereotactic treatments such as SBRT, which corrects for CC dose overestimations without increasing OAR doses. References: [1] Koto, M., Takai, Y., Ogawa, Y., Matsushita, H., Takeda, K., Takahashi, C., ... & Yamada, S. (2007). A phase II study on stereotactic body radiotherapy for stage I non-small cell lung cancer. Radiotherapy and Oncology, 85(3), 429-434.[2] van Zyp, N. V. D. V., Hoogeman, M. S., Heijmen, B. J. M., Van de Water, S., & Nuyttens, J. J. (2009). Implementing Monte Carlo dose calculation in the treatment of non–small cell lung cancer (NSCLC): clinical consequences. International Journal of Radiation Oncology, Biology, Physics, 75(3), S450. Keywords: SBRT, Monte Carlo, Lung cancer,
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