S1888
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
0.90 (range 0.81-0.97). Conclusion:
control.6,7 . This study evaluates the dosimetric feasibility of HFRT with central SIB in unresectable or medically inoperable RPS, using a cohort of patients previously treated with preoperative RT. Material/Methods: Fifteen patients with RPS treated at our institution between 2017-2023 with preoperative RT were replanned using HFRT with central SIB. 4D-CT was used to contour internal gross tumor volume (iGTV), which was expanded by 1.5 cm and edited per expert consensus guidelines to form the clinical target volume (CTV).9 CTV was isotopically enlarged by 5mm to form the planning target volume (PTV). SIB volume was created by isotopically contracting iGTV by 1cm. HFRT organ-at-risk (OAR) constraints were derived using EQD2 calculations and published values (Table 1). OAR constraints were prioritized during optimization. For tumors involving the ipsilateral kidney, unilateral constraints were applied to contralateral kidney. Volumetric modulated arc therapy plans were generated for 15-fractions, with 42.75Gy to PTV, 45Gy to iGTV, and 52.5Gy to SIB; homogeneity index (HI) and conformity index (CI) were calculated(Table 2). Feasibility was assessed by evaluating whether target coverages could be achieved while meeting OAR constraints.
HFRT with a central SIB appears to be dosimetrically feasible for patients with unresectable or medically inoperable RPS. This approach may warrant prospective study to evaluate the safety and clinical outcomes in this patient population. References: 1. Kumar V et al. Indian J Surg Oncol. 20122. Jolissaint JS et al. Curr Oncol Tor Ont. 20233. Farooqi AS et al. Curr Oncol. 20234. Bonvalot S et al. Lancet Oncol. 20205. Callegaro D et al. Ann Surg. 20236. Lee JW et al. Adv Radiat Oncol. 20207. Burner DN et al. Adv Radiat Oncol. 20258. Guadagnolo BA et al. Lancet Oncol. 20229. Baldini EH, et al. Int J Radiat Oncol Biol Phys. 2015 Keywords: Hypofractionation, Retroperitoneal Sarcoma STEREOTACTIC RADIOSURGERY FOR THE TREATMENT OF OCULAR MELANOMA Nestor Aragon Martinez 1 , María del Rocío Toledo Elizalde 1 , Abel Hernández Guzmán 2 , Ana Carolina Ahumada Pamanes 1 , David Ancona 1 1 Radiotherapy, Hospital San Jóse TecSalud, Monterrey, Mexico. 2 Radiotherapy, Hospital San Jóse TecSalud, Mexico, Mexico Purpose/Objective: Ocular cancer in Mexico represents a challenge due to its low incidence and because many tumors are asymptomatic and located in non-visible areas. Digital Poster 2523 Another challenge is the limited access to specialized equipment and multidisciplinary teams across the country, which may delay diagnosis and treatment. Depending on the type of tumor, management ranges from observation to eye-preserving techniques such as stereotactic radiosurgery (SRS), in which 21 Gy are delivered in a single fraction. This work describes the procedure for ocular melanoma radiosurgery, as well as the challenges related to immobilization, target volume identification, and rigorous quality controls necessary for accurate treatment delivery. Material/Methods: Treatments were delivered using a linear accelerator equipped for stereotactic radiosurgery. The system undergoes routine quality assurance tests ensuring sub-millimeter accuracy (<1 mm) for gantry, couch, and collimator rotations, in accordance with international SRS recommendations.Before treatment, the ophthalmologist places two or three carbon fiducials at the lesion borders to enable precise localization on MRI and CT imaging. On the treatment day, the ophthalmologist performs ocular block
Results: Mean size of tumors was 18.3cm (range 5.8-28.2cm) with mean volumes for iGTV, SIB, and PTV of 1633.8cc, 926.9, and 3323.2cc, respectively. All non-bowel OAR constraints were met, and no bowel constraints exceeded limits by >1%. All plans surpassed the metric for PTV and SIB coverage, 14 plans surpassed metric for iGTV coverage, with one plan slightly underdosed (V98%=93.5%) to meet OAR constraints. The average HI of the iGTV and SIB were 0.21 (range 0.18-0.27) and 0.05 (range 0.04-0.06), respectively. The CI average was
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