ESTRO 2025 - Abstract Book

S349

Brachytherapy - Physics

ESTRO 2025

At Cambridge University Hospitals, the DaRT-V trial was set up to assess DaRT for the treatment of squamous cell carcinoma of vulva. We report our experience of commissioning a TPS for a novel treatment with a unique mechanism of action which intersects sealed source and unsealed source dosimetry. Material/Methods: The TPS provided by Alpha Tau for DaRT pre- and post-implant dosimetry was MIM Symphony Alpha DaRT v7.2. We decided to base our commissioning on Table 4.4 in IPEM Report 81 [2] which outlines a set of commissioning tests to be performed for a conventional brachytherapy TPS while making adjustments for the unique characteristics of DaRT sources. Dose distributions in MIM were compared to those produced using a MATLAB program provided by Alpha Tau, which generates dose data using an adapted TG43 model [3], and data produced by Heger et al. [4] using COMSOL Multiphysics simulations. Results: Many DaRT source data tests were trivial to perform, as were source reconstructions. Dose distributions and comparisons were more challenging, in part due to steep dose gradients and limited published data. Dose profiles generated using MIM demonstrated good agreement within 5% of the published data in the clinically relevant range of 0.5-4.5mm. We found that the doses generated by MIM were slightly lower than those in the published data. Two tests in Report 81 were not adaptable for DaRT: tissue attenuation and scatter factors, and standard source arrangements. The former was deemed not relevant due to the mechanism DaRT uses to distribute dose in tissue, while for the latter no standard arrangements exist. Conclusion: MIM passed all the tests adapted from Report 81 it was assessed against. Future work should focus on providing formal guidance for commissioning specific to DaRT. [1] Popovtzer A, et al. Extended Follow-Up Outcomes from Pooled Prospective Studies Evaluating Efficacy of Interstitial Alpha Radionuclide Treatment for Skin and Head and Neck Cancers. Cancers (Basel). 2024;16(13). [2] IPEM Report 81. Physics Aspects of Quality Control in Radiotherapy. [3] Heger G, Arazi L. Technical Note: adapting the TG-43 formalism for use in Diffusing alpha-emitters Radiation Therapy. [4] Heger G, et al. Alpha dose modeling in diffusing alpha-emitters radiation therapy-Part I: single-seed calculations in one and two dimensions. Med Phys. 2023 Mar;50(3):1793-1811. Keywords: DaRT, Alpha, Commissioning References: Digital Poster A novel open source QA patient specific 3D software for HDR treatments Albert Bartrés, Nagore García, Verónica Alba, Vicent Pastor, Iñigo Gonzalez, Sergio Panzuela, Maddalen Alonso, Jose Rochera, José Ramón Puertolas, Francisco Lozano, Melanie Erzilbengoa Medical Physics, Onkologikoa/HUD, Donostia, Spain Purpose/Objective: Historically, in radiotherapy treatments with linear accelerators, various methods have been available for the dosimetric verification of these treatments. One of these methods is double calculation, which, in summary, is based on recalculating the doses received while considering the parameters of the established plan. In brachytherapy, specifically in HDR treatments, all these methods are either technically unfeasible or have not been sufficiently developed. The present software aims to provide a new calculation for treatments based on the files generated from the TPS plan. This calculation, unlike those currently developed in a non-commercial manner, does not rely solely on 3453