ESTRO 2025 - Abstract Book

S2798

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: For multi-arc non-coplanar VMAT treatment delivery of SRS, the dominant predictive factor for reducing extracranial dose is removal of the vertex arc. This does not compromise plan quality for the single benign lesions examined and fulfils the NHS England SRS specification for achieving less than 20mGy at 30cm inferior to target [2].

Keywords: SRS, extracranial dose, HyperArc

References: [1] X. G. Xu, B. Bednarz, and H. Paganetti, “A review of dosimetry studies on external-beam radiation treatment with respect to second cancer induction,” Jul. 07, 2008, Institute of Physics Publishing . doi: 10.1088/0031-9155/53/13/R01. [2] NHS England. (18 September 2024). NHS England Service specification: stereotactic radiosurgery and stereotactic radiotherapy (intracranial) (teenage, young adults and adults). [online] england.nhs.uk. Available at: https://www.england.nhs.uk/publication/service-specification-srs-intracranial-teenage-young-adults-and-adults/ [Accessed 18 Nov. 2024].

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Poster Discussion Improved Dosimetric Sparing in Esophageal Cancer Radiotherapy Using VMAT with Dynamic Collimator Rotation and Modulated Ports: A Comparative Study Michael Salerno 1 , Melissa Vila 1 , Yin Gao 1 , Taoran Li 1,2 , Lei Dong 1 , Kevin Teo 1 1 Radiation Oncology, University of Pennsylvania, Philadelphia, USA. 2 Medical Affairs, Varian Medical Systems, Palo Alto, USA Purpose/Objective: A novel solution, RapidArc Dynamic-RAD (Varian Medical Systems, Palo Alto, USA) has been implemented to combine VMAT with IMRT-like modulated ports, including the use of a dynamic collimator. The study focused on comparing the plan quality and planning efficiency of RAD against conventional VMAT in the treatment of esophageal cancer. Particular emphasis was placed on the impact of RAD on organ-at-risk (OAR) doses while ensuring robust target coverage. Material/Methods: 10 previously treated esophageal cancer patient cases (5 involving upper esophagus and 5 involving lower esophagus) were selected. Each patient was planned using both conventional VMAT and RAD approaches. RAD plans included four empirical static gantry angles as a class-solution (340°, 280°, 181°, and 80°; see Fig.1) optimized with dynamic collimator rotation. For each case, four unique RAD plans were generated: (1) a balanced approach prioritizing both target and OAR sparing, (2) a target-focused plan emphasizing heart sparing, (3) a target-focused plan emphasizing lung sparing, and (4) a conventional VMAT plan with two continuous arcs. Consistent optimization parameters were applied across all plans using a 6MV beam and a prescription dose of 4500 cGy delivered over 25 fractions. All plans were normalized to PTV D95% = 95%. For three patients, minor modifications to port angles and weighting were made to improve plan quality. Planning times for each approach were recorded, and dose metrics were statistically analyzed using paired t-tests (p ≤ 0.05). Results: RAD demonstrated significant reductions in both lung and heart doses when compared to conventional VMAT. The balanced RAD plan reduced lung D40% by 0.57Gy±0.64Gy (p=0.02), lung D0.03cc by 2.28%±2.03% (p=0.006), and lung V5Gy by 5.35%±6.08% (p=0.02). For the lung-focused RAD plan, lung D20% and V5Gy decreased by 1.7Gy±1.75Gy (p=0.02) and 5.46%±3.63% (p=0.002), respectively among others. Heart-focused RAD demonstrated robust heart sparing, significantly reducing heart Dmean by 2.75Gy±1.43Gy (p=0.001) and D50% by 3.08Gy±2.28Gy (p=0.007). Despite a small increase in lung V20Gy (~1%) for balanced and heart-focused RAD plans, all dose metrics