S1889
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 2545
anesthesia to weaken the extraocular muscles and minimize natural eye motion, which induces proptosis. Subsequently, a high-resolution MRI and CT simulation are performed using a thermoplastic immobilization mask system, following the institution’s internal SRS protocol.The images are imported into the treatment planning system and fused based solely on fiducials to minimize the influence of proptosis. The radiation oncologist contours the tumor and organs at risk, including the retina, lenses, lacrimal glands, and optic nerves. The medical physicist then designs a treatment plan consisting of three arcs between 60° and 90°, with couch rotations (Figure 1). Dose calculation is performed using a Monte Carlo algorithm, prescribing 21 Gy to the target volume with an optimized dose distribution to minimize exposure to healthy tissues. The calculation grid resolution is set to 1 mm. Quality assurance is performed using radiochromic film and a dedicated head phantom. Finally, the eye is re-blocked and the treatment is delivered using a six-degree-of- freedom couch. Results: Patient-specific quality assurance demonstrated that treatment can be safely administered, provided that the mechanical and geometric precision limits of the equipment are respected. (see Figure 1)
A Novel Treatment Planning Technique Approach Combining Efficiency and Brain Sparing for Scalp Radiotherapy with RapidArc Dynamic HAE-JIN PARK, MI-HWA KIM, JINA KIM, O KYU NOH, SEUNG YEUN CHUNG, YOUNG-TAEK OH, MISON CHUN, OYEON CHO, JAESUNG HEO Radiation Oncology, Ajou University School of Medicine, Suwon, Korea, Republic of Purpose/Objective: Scalp irradiation remains technically challenging due to its irregular convex geometry and large target area requiring homogeneous dose coverage with adequate skin and brain sparing, further complicated by the limitations of conventional treatment techniques. A novel solution, RapidArc Dynamic (RAD) (Varian Medical Systems, Palo Alto, USA), integrates dynamic collimator rotation and static angle modulated ports (STAMPs) with VMAT, combining the conformality of VMAT with IMRT-like modulation. This study evaluated the dosimetric performance and clinical feasibility of RAD plans for scalp irradiation compared with VMAT. Material/Methods: Eleven patients treated for scalp irradiation were retrospectively analyzed. All plans were generated in Eclipse v18.1 using the AcurosXB algorithm. Four plans were created for each patient using identical contours, prescriptions, and institutional clinical constraints to directly assess technique-specific effects. These included a single-arc RAD plan (P1) as baseline, a single-arc RAD with skin flash (P2) for enhanced surface coverage, a conventional four-arc RapidArc (P3) as reference, and a virtual RAD plan (P4) optimized with the RAD algorithm while maintaining the P3 geometry. Plan quality was evaluated using DVH-based parameters (D98, D95, D2, CI, HI). Two radiation oncologists independently performed blinded reviews assessing dose distribution, clinical acceptability, and overall plan preference. Results: All plans were prescribed to 60 Gy in 30 fractions and normalized to identical target coverage. Both RAD- based plans (P1 and P2) demonstrated a marked reduction in normal brain dose—approximately 45– 60% lower mean and volumetric exposure (V5–V45 Gy) compared with P3 and P4, confirming the superior brain-sparing efficiency of the RAD technique. While P3 and P4 showed slightly lower PTV Dmax and improved homogeneity—particularly P4 with HI < 0.10—P1 and P2 maintained clinically acceptable uniformity with significantly reduced brain exposure. OAR analysis revealed higher brainstem and chiasm Dmax in P3 and P4, whereas all plans met tolerance for eyes, parotids, and lenses. Between the RAD plans, P2 improved surface coverage in several cases but
Conclusion: The delivery of stereotactic radiosurgery treatments for ocular melanoma is feasible in accordance with international recommendations, as long as strict and standardized protocols are implemented to ensure treatment safety and accuracy. References: Messineo D., Barile G., Morrone S., La Torre G., Turchetti P., Accetta L., et al. Meta-analysis on the utility of radiotherapy for the treatment of Ocular Melanoma. Clin Ter. 2020;171:e94–e96. doi: 10.7417/CT.2020.2195.Yazici G., Kiratli H., Ozyigit G., Sari S.Y., Cengiz M., Tarlan B., Mocan B.O., Zorlu F. Stereotactic radiosurgery and fractionated stereotactic radiation therapy for the treatment of uveal melanoma. Radiat Oncol Biol. 2017;98:152–158. Keywords: Linac, High dose, Cones
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