S1778
Physics - Dose prediction/calculation, optimisation and applications for particle therapy planning
ESTRO 2026
imaging for radiotherapy treatment planning: current status and future directions-a review. Br J Radiol 88(1051). Keywords: Adaptive, hypoxia, OSMK
be explained by the lower OER for high LET particles. Due to the necessary boost of physical dose and LETd in the GTV, dose to the left and right lungs increase with hypoxia. As has been shown in [1], increased target LETd also results in plans which are less robust against range uncertainties.
Digital Poster 4386 A novel spatially fractionated radiotherapy strategy based on VMAT and CyberKnife synergy Yi Peng, Ke Yuan, Feng Yang, Xin Xin, Junxiang Wu, Tianli Qiu, Xianliang Wang Department of Radiation Oncology, Sichuan Cancer Hospital and Institute, Chengdu, China Purpose/Objective: Spatially fractionated radiation therapy (SFRT) delivers high-dose radiation to specific subvolumes within the gross tumor volume (GTV) while minimizing toxicity to surrounding normal tissues. While VMAT-based SFRT yields relatively low peak-to-valley dose ratio (PVDR) and average dose ratio (ADR) due to hardware limitations, CyberKnife achieves superior PVDR and ADR values. However, CyberKnife becomes clinically impractical for large GTVs due to prolonged treatment times. To address this, we developed a novel hybrid SFRT strategy: CyberKnife delivers high doses to lattice points, while VMAT provides low-dose coverage to the entire GTV. This approach maintains high PVDR and ADR while ensuring clinically feasible treatment durations. Material/Methods: A retrospective analysis was conducted on 16 approved SFRT plans (10 VMAT and 6 CyberKnife cases) for head/neck tumors (volume range: 52.04– 770.82 cc), evaluating dose distribution and treatment time. Additionally, a novel SFRT strategy combining VMAT and CyberKnife was applied to 8 head/neck tumor cases (volume range: 66.74–583.22 cc). The GTV was manually delineated, followed by an automated program to generate 3D spherical lattice points arranged in a hexagonal close-packed (HCP) pattern within the GTV. In the hybrid SFRT approach, CyberKnife delivered high-dose irradiation to lattice points, while VMAT provided low-dose coverage to the entire target volume. Results: In SFRT plans, lattice points were isolated by applying 60% of the prescribed dose. Dosimetric analysis revealed that VMAT achieved a PVDR of 2.14 ± 0.23 and an ADR of 2.32 ± 0.37, while CyberKnife yielded a higher PVDR (3.26 ± 0.33) but a lower ADR (2.01 ± 0.46). Notably, for tumors exceeding 250 cc, CyberKnife required over 60 minutes of treatment time, rendering it clinically impractical. However, the novel SFRT strategy maintained treatment time within 60 minutes for large-volume tumors while achieving a
Conclusion: A biological adaptive workflow based on biomarkers can be used to maintain satisfactory target coverage in the presence of biological variations. Just like geometrical adaptative workflows enable smaller margins in the nominal plan, biological adaptation may be used to avoid nominal plans with unnecessarily high LETd. References: [1] Fredriksson, A, et al. (2023). The LET trilemma: Conflicts between robust target coverage, uniform dose, and dose-averaged LET in carbon therapy. Medical Physics, August, 1–11.[2] Inaniwa, T, et al. (2021). Adaptation of stochastic microdosimetric kinetic model to hypoxia for hypo-fractionated multi- ion therapy treatment planning. Physics in Medicine and Biology, 66(20).[3] Masuda, T, et al. (2025). Design of multi-ion therapy for head and neck cancers using carbon-, oxygen-, and neon-ion beams: potential efficacy against tumor hypoxia. Physics in Medicine and Biology, 70(8). [4] Thorwarth D. (2015). Functional
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