S1949
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Results:
manipulate PTV dose escalation. For plans with more than 10 PTVs, improving the CI is feasible using MU limit modulation up to a point, after which no further improvement occurs.In SRS planning, the HyperArc optimiser does not routinely include organs at risk (OARs) unless they are located near target volumes. Among the selected cases, few targets were in close proximity to OARs, and consequently no clear dosimetric trends were identified.Excessive modulation may reduce plan deliverability, and in house data show a negative correlation between QA pass rates and MU/Gy3. Future work is needed to establish practical MU limits that balance plan quality, deliverability, and clinical efficiency in HyperArc SRS. References: 1. Vergalasova I, Liu H, Alonso-Basanta M, et al. Multi-institutional dosimetric evaluation of modern day stereotactic radiosurgery (SRS) treatment options for multiple brain metastases. Front Oncol. 2019;9(JUN). doi:10.3389/fonc.2019.004832. Gaudreault M, Nguyen PH, Lawford C, Franich R, Hardcastle N. Implementations of modulation complexity scores and their correlations with treatment plan quality in stereotactic radiation therapy. Med Phys. 2025;52(7). doi:10.1002/mp.179613. 2025, Adelaide, Australia. Keywords: SRS, Brain metastases, monitor units Digital Poster 3777 Single arc dynamic collimator VMAT with automated gradient optimization enables highly efficient planning for stereotactic spine radiosurgery Shu-Fan Wang 1 , Pei-Wen Lee 1 , Chia-Jung Wu 1 , Feng- Ming Hsu 1,2 1 Department of Radiation Oncology, National Taiwan University Cancer Center, Taipei, Taiwan. 2 Department of Radiation Oncology, National Taiwan University Hospital, Taipei, Taiwan Purpose/Objective: Stereotactic spine radiosurgery (SSRS) delivers escalated radiation dose while sparing adjacent organs at risk. Conventional VMAT planning requires multiple arcs and ring-based dose-limiting structures (DLS) to achieve high conformity and sharp dose fall- off. The RapidArc Dynamic (RAD) algorithm enables dynamic collimator rotation during arc delivery, whereas the SBRT normal tissue optimization (SBRT NTO) provides automated gradient control1. This study aimed to evaluate the planning quality and efficiency of DLS-based VMAT (VMATDLS) compared with SBRT NTO-based RAD planning (RADSBRT-NTO).
Gustafsson et al, IUPSEM
For both the Low PTV and High PTV groups, the average Dmax increased with higher numbers of MUs (Fig 1a). The effect was more pronounced for plans with more than 10 PTVs. The average CI improved (closer to 1.0) with increasing MU/Gy up to 650 MU/Gy for the High PTV cohort, then plateaued. There was no overall trend in CI for plans with fewer than 10 PTVs (Fig 1b).No consistent trends were observed across most OARs. However, in certain instances, increased modulation was associated with higher doses (Fig 1c). Conclusion: Monitor unit limits influence plan quality differently depending on the number of targets. For both Low PTV and High PTV plans, it was shown that increased modulation increased target dose max. An implication is that MU limits could potentially be used to
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