S104
Brachytherapy - Head & neck, skin, eye
ESTRO 2026
high viscosity silicone rubber for custom made molds in HDR plesiotherapy. In National Congress of the Spanish Medical Physics Society (SEFM), Valencia, Spain.
Digital Poster 4324
Role of alginate in managing the air gap in contact brachytherapy for auricular non-melanoma skin cancer Bruno Fionda 1 , Enrico Rosa 1,2 , Elisa Placidi 1 , Maria Vaccaro 1 , Valentina Lancellotta 1 , Maria Concetta La Milia 1 , Pierpaolo Dragonetti 1 , Maria Antonietta Gambacorta 1,3 , Marco De Spirito 1,4 , Luca Tagliaferri 1,3 1 Dipartimento di Diagnostica per Immagini e Radioterapia Oncologica, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 2 Department of Theoretical and Applied Sciences, eCampus University, Novedrate, Italy. 3 Dipartimento di Scienze radiologiche, Università Cattolica del Sacro Cuore, Rome, Italy. 4 Dipartimento di Neuroscienze, Università Cattolica del Sacro Cuore, Rome, Italy
Purpose/Objective: Interventional radiotherapy (IRT, modern
brachytherapy) is an effective modality for treating non-melanoma skin cancer (NMSC). In the auricular region, the intricate curvature of the ear often produces air gaps between the applicator and the skin, potentially compromising dose uniformity. This study assesses the dosimetric impact of air gaps and investigates the role of alginate as a supportive material to improve dose coverage and applicator conformity. Material/Methods: Five patients with auricular NMSC underwent high- dose-rate IRT. Treatment plans were initially calculated with the TG-43 formalism [1] and subsequently recalculated with TG-186 [2], which accounts for heterogeneities and material density variations. Dose– volume histogram (DVH) parameters were analyzed for both the clinical target volume (CTV: V150, V100, V95) and external body (V150, V100, V50). The dosimetric influence of air gaps and the potential bolus effect of alginate were evaluated. Results: Air gaps introduced minor dose perturbations that were mitigated by the presence of alginate. Differences between TG-43 and TG-186 calculations were not statistically significant but TG-186 provided more accurate modeling of dose attenuation in heterogeneous geometries.
Results: For the initial case (PTV thickness 5 mm), dosimetry was optimal, with surface doses <150% of prescription and V90 >100%, achieving superior dose conformity compared to electrons. Treatment was well tolerated, with acute grade 1–2 radiodermatitis, no chronic toxicities, and complete lesion response. Based on this experience, we established an HDR contact brachytherapy protocol for T1–T2 PCBCLs with <5 mm thickness. All patients undergo staging by Hematology confirming skin-limited disease, supplemented by PET- FDG and CT imaging to verify lesion thickness. Prescription doses follow international guidelines: 20– 36 Gy to 90% of the PTV, lower for marginal zone PCBCL and higher for follicular center PCBCL, in conventional fractionation (2 Gy/session, five sessions/week). Although lower doses (<12 Gy) have been reported for indolent lesions, we have not yet adopted this regimen. Conclusion: HDR contact brachytherapy is a viable alternative to electron beam EBRT for T1–T2 PCBCLs ≤ 5 mm thick, providing comparable oncologic response and toxicity, superior dose conformity, and excellent cosmetic outcomes. Keywords: Lymphoma, Contact, Molds References: [1] Sanz Freire CJ, Pérez Echagüen, S, Ossola Lentati, GA (2015, June). Dosimetric characterization of a very
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