S126
Brachytherapy - Physics
ESTRO 2026
1.Limandjaja GC, Niessen FB, et.al. Hypertrophic scars and keloids: Overview of the evidence and practical guide for differentiating between these abnormal scars. Exp Dermatol. 2021 Jan;30(1):146-161. doi: 10.1111/exd.14121. Epub 2020 Jul 6. 2.Lee SY, Park J. Postoperative electron beam radiotherapy for keloids: treatment outcome and factors associated with occurrence and recurrence. Ann Dermatol. 2015 Feb;27(1):53-8. doi: 10.5021/ad.2015.27.1.53. Epub 2015 Feb 3. 3.Ilori EO, Campbell SR, et.al. Adjuvant intensity-modulated radiotherapy improves outcomes for resected complex keloids. JAAD Case Rep. 2022 May 28;25:47-52. doi: 10.1016/j.jdcr.2022.05.017. Digital Poster 2041 Validation of the advanced collapsed cone engine for contact brachytherapy of the skin Freja Alpsten 1,2 , Christian Valdes-Cortez 3 , Apostolos Raptis 2 , Åsa Carlsson Tedgren 2,1 1 Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden. 2 Department of Nuclear Medicine and Medical Physics, Karolinska University Hospital, Stockholm, Sweden. 3 Nuclear Medicine Department, Hospital Regional de Antofagasta, Antofagasta, Chile Purpose/Objective: Recent studies have shown differences between model-based dose calculation algorithms (MBDCAs) and the TG-43 formalism for contact brachytherapy of the skin.1,2 To improve understanding of the influence of materials on dose in skin brachytherapy, complementary dose reporting using MBDCAs should be utilized.3Oncentra Brachy® (OcB) TPS with the MBDCA ACE is available at our clinic. ACE has been validated for several treatment sites;4,5 however, limited data exist on skin treatments. This work aims to validate ACE against Monte Carlo (MC) for skin brachytherapy using the Freiburg flap applicator, and to compare with the TG-43 method. Material/Methods: 2 scalp and 2 nose treatments were included. Each case consists of a virtually created phantom CT, designed to mimic real patient cases treated at our hospital. The CT resolution was 1 mm3, each material was assigned to a specific HU value, and all voxels contained one material only.The MC toolkit TOPAS was used as a benchmark. TOPAS has been previously validated by Berumen et. al.,5 however, to ensure correct implementation, we validated our TOPAS setup according to the TG-186 recommendations.3,7,8Treatment plans were created in OcB using the Ir192 Flexisource. Structures were delineated with the HU thresholding tool. Tissue compositions and densities were defined in
approval was recorded for both techniques. Target dose coverage (PTV D98, D99 and D50) and doses to organs of interest (humerus and ipsilateral lung) were evaluated with both plans were normalized to the same prescription dose. Results:
The total planning duration recorded from contouring process to clinician approval, found to be comparable for both techniques, averaging approximately two hours in each technique. VMAT achieved similar target coverage, with more homogenous distribution and superior organs sparing. Surface brachytherapy yielded higher median and central doses with significantly increased doses to adjacent structures. These differences stem from two factors; 1) geometric, with the curved applicator over the shoulder shortened the source-to-tissue distances, and 2) algorithm, with the AAPM TG-43 formalism assumed a water-equivalent medium, without taking into account the attenuation by air and bone. VMAT planned with heterogeneity-corrected algorithm, produced smoother dose gradients with inverse optimization contributes to improved target dose conformity. Clinically, surface brachytherapy allows immediate post-operative treatment and high surface dosing which is advantageous for residual keloid cells control, but at the extent of higher dose spillage to bone and lung. VMAT offers greater dosimetric precision and reproducibility, though it requires more complex setup and workflow. A practical solution is a ‘hybrid-bridge’ approach; administering an initial brachytherapy fraction within 24 hours, followed by VMAT fractions. Conclusion: Surface brachytherapy offers the advantage of immediate post-operative irradiation and excellent surface dose deposition while VMAT provides heterogeneity-corrected, high dose conformity and superior organs sparing. Combination of both techniques leverages the timeliness and biological benefit of brachytherapy with the dosimetric precision and safety of VMAT, hence expected to yield superior local control post-operative keloid radiotherapy. Keywords: post-operative keloid, surface brachytherapy, VMAT References:
Made with FlippingBook - Share PDF online