S107
Brachytherapy - Head & neck, skin, eye
ESTRO 2026
Rome, Italy. 4 Dipartimento di Scienze Radiologiche, Università Cattolica del Sacro Cuore, Rome, Italy
materially affects brachytherapy dose shaping. Incorporating curvature, particularly concave designs, can broaden the therapeutic window and improve homogeneity in challenging anatomies. Prospective work will focus on clinical validation and the development of curvature-specific applicators for optimized treatment. Keywords: Interventional Radiotherapy, skin, curvature References: [1] Fionda, Bruno, et al. "Multilayer intensity modulated contact interventional radiotherapy (brachytherapy): Stretching the therapeutic window in skin cancer." Journal of Contemporary Brachytherapy. Digital Poster 4547 Dosimetric impact of tumor morphology in Ruthenium-106 ocular interventional radiotherapy (modern brachytherapy) Elisa Placidi 1 , Sofia Raponi 2 , Enrico Rosa 1,3 , Monica Maria Pagliara 4 , Bruno Fionda 1 , Maria Vaccaro 1 , Maria Antonietta Gambacorta 5,1 , Luca Tagliaferri 1,5 , Marco De Spirito 1,2 1 Dipartimento di Diagnostica per Immagini e Radioterapia Oncologica, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 2 Dipartimento di Neuroscienze, Università Cattolica del Sacro Cuore, Rome, Italy. 3 Department of Theoretical and Applied Sciences, eCampus University, Novedrate, Italy. 4 Dipartimento Neuroscienze, Organi di Senso e Torace, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 5 Dipartimento di Scienze Radiologiche, Università Cattolica del Sacro Cuore, Rome, Italy Purpose/Objective: This study investigates the dosimetric impact of tumor morphology in Ruthenium-106 (Ru-106) ocular interventional radiotherapy (IRT, modern brachytherapy), aiming to quantify how variations in three-dimensional tumor shape influence dose distribution, volumetric coverage, and clinically relevant metrics such as D99% and mean tumor dose. Material/Methods: Simulations were conducted using Plaque Simulator™ (Eye Physics, USA) to model tumors with circular bases (10 × 10 mm ² ) and thicknesses from 1.5 mm to 6 mm, representing typical uveal melanoma geometries. Four internal tumor morphologies were analyzed—dome, mushroom (stem and ball variants), and conical— combined with five Ru-106 plaques (CCB, CCC, CCD, COB, and CIB; Eckert & Ziegler BEBIG, Germany). A prescribed dose of 100 Gy at the tumor apex was used
Purpose/Objective: Contact interventional radiotherapy (IRT, modern brachytherapy) is widely adopted for non-melanoma skin cancers. Curved applicators may improve dose conformity on complex surfaces. We quantify how curvature impacts dose distribution and introduce the “Nautilus Effect.” Material/Methods: In-silico plans were generated for twelve curvature configurations using Oncentra Brachy (Elekta). Twelve ROIs were contoured as three-dimensional circular crowns (uniform thickness t = 5 mm) (Figure 1). For each configuration, three catheters were activated with identical numbers of dwell positions and dwell times. The primary endpoint was the therapeutic window (TW), defined as the distance between the 100% and 150% isodoses [1]; additional metrics included mean dose and dose uniformity.
Results: Applicator curvature strongly modulated dose distribution. With increasing concavity, the TW expanded from 4.3 mm to 10.4 mm, enhancing coverage in anatomically curved regions. Conversely, increasing convexity reduced TW from 4.1 mm to 3.3 mm (Figure 2). The Nautilus Effect describes the tendency of curved applicators to deliver a higher mean dose to more highly curved CTVs. Greater concavity also improved uniformity.
for all configurations. For each plaque–tumor combination, dose–volume histograms were
Conclusion: Curvature is a controllable geometric parameter that
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