S1919
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
RiL during brain radiotherapy [3]. Material/Methods:
We retrospectively analyzed 28 GBM patients treated with either IMRT or VMAT. The tumor volume was 296.4±150.3 cm ³ , within the range [56.6 – 719] cm ³ (Fig 1). For each patient treated with IMRT, an alternative VMAT plan was created, and vice versa for patients treated with VMAT. The Replanning used the identical planning CT and dose constraints as the corresponding clinical plans to ensure comparable optimization criteria.A 4D dosimetric blood-flow model simulated patient-specific beam delivery gantry rotation/segment timing (Fig1), and systemic blood circulation to estimate the cumulative dose to CLs for both the clinical and the alternative plan [3]. A cerebrovascular model was used to simulate the explicit trajectories of blood particles through the irradiated field in the brain (Fig 1).Primary endpoints: 1) to calculate the DVH of the CLs and total blood volume receiving any non-zero dose (see Fig 2a), and 2) to estimate fraction of CLs depleted at end of each treatment. Paired comparisons were performed between IMRT and VMAT.
Conclusion: With respect to RiL, our model found that VMAT is preferable for GBM patients with CTV volumes >100 cm ³ , while IMRT may be more beneficial for smaller CTVs or tumors. References: [1] Grossman S.A., Y. X. (2011). Immunosuppression in patients with high-grade gliomas treated with radiation and temozolomide. Clin Cancer Res.17, 5473–5480. https://doi.org/10.1158/1078-0432.CCR- 11-0774.[2] Grossman, S. E. (2015). Survival in Patients With Severe Lymphopenia Following Treatment With Radiation and Chemotherapy for Newly Diagnosed Solid Tumors. Natl Compr Canc Netw.13(10), 1225-31. doi: 10.6004/jnccn.2015.0151.[3] Hammi. (2023). 4D dosimetric-blood flow model: impact of prolonged fraction delivery times of IMRT on the dose to the circulating lymphocytes. Physics in medicine and biology, 68(14), 10.1088/1361- 6560/acdcdc. https://doi.org/10.1088/1361- 6560/acdcdc. Keywords: Lymphopenia, Glioblastoma, dose rate VMAT IMRT Digital Poster 3178 Evaluation of Commercial Cone Beam Computed Tomography Enhancement Algorithms for Improving Hounsfield Unit Accuracy in Adaptive Radiotherapy Chi Wah Kong, Bin Yang, Pak Hang Nam, Chen Yu Huang, Mei Yan Tse, Ka Ki Lau, Pei Xiong Li, Kin Yin Cheung, Siu Ki Yu Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong Purpose/Objective: This study evaluates the efficacy of three commercially available image enhancement algorithms in improving Hounsfield Unit (HU) accuracy within Cone Beam Computed Tomography (CBCT) images, utilizing reference planning CT scans, to enhance their applicability in adaptive radiotherapy protocols. Material/Methods: A Sun Nuclear Tomo-phantom HE equipped with
Results: In patients with smaller CTVs (<100 cm ³ ), VMAT irradiated, on average, 4.6% ± 4.9% more CLs volume per fraction compared to IMRT. Conversely, for larger CTVs (>100 cm ³ ), IMRT irradiated 14.0% ± 5.4% more CLs volume (Fig 2b).Our simulations indicated that by the third treatment fraction, IMRT had irradiated >90% of the total CLs population on averageversus 77% with VMAT. By the end of the full fractionated course, 77% (IMRT) and 73% (VMAT) of the total blood pool had received at least a dose (>300 mGy). Overall, the estimated mean depletion of CLs was significantly higher for IMRT than VMAT (13.9 ± 6.4% vs 12.8 ± 5.6%), with a mean paired difference of 1.0 ± 1.7%, and CI95% [0.3, 1.7], and a paired t-test, p = 0.003) (Fig 2c).
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