ESTRO 2025 - Abstract Book

S2786

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

The single prescription dose plans have a higher CI than the equivalent multiple prescription dose plans. This is due to the fact that the single prescription dose was always chosen based on the largest metastasis, making it equal to the lowest of the equivalent multiple prescription doses. As expected, GI scores for plans with multiple prescription doses are similar to those for plans with the equivalent single prescription dose. Conclusion: Our proposed method to calculate CI and GI for plans with multiple prescription doses is straightforward to implement and allows comparisons with data from historical single prescription dose plans. References: 1. Zindler JD, Bruynzeel AME, Eekers DBP, Hurkmans CW, Swinnen A, Lambin P. Whole brain radiotherapy versus stereotactic radiosurgery for 4-10 brain metastases: a phase III randomised multicentre trial. BMC Cancer. 2017 Jul;17(1):500. https://doi.org/10.1186/s12885-017-3494-z 2. Paddick I. A simple scoring ratio to index the conformity of radiosurgical treatment plans. J Neurosurg. 2000; 93:219-222. https://doi.org/10.3171/jns.2000.93.supplement_3.0219 3. Paddick I, Lippitz B. A simple dose gradient measurement tool to complement the conformity index. J Neurosurg. 2006;105 Suppl:194-201. https://doi.org/10.3171/sup.2006.105.7.194 1837 Digital Poster Towards a workflow in MR-LINAC without CTs. Establishing our own library of electronic densities for prostate patients. Teresa Cuenca 1 , María Yáñez 1 , Benigno Barbés 1 , Sara Fadrique 2 , Haizea Etxeberria 2 , Javier Burguete 3 1 Department of Radiation Physics, Clinica Universidad de Navarra, Pamplona, Spain. 2 Department of Radiation Oncology, Clinica Universidad de Navarra, Pamplona, Spain. 3 Department of Physics and Applied Mathematics, Universidad de Navarra, Pamplona, Spain Purpose/Objective: The aim of this work is to analyse the feasibility of implementing an MR-only workflow for prostate cancer treatments in MR-LINAC, using the department's own calculated electronic densities (ED) without needing a CT planning, avoiding unnecessary patient doses and improving the department's time and staff resources. Material/Methods: 88 male pelvis CT scans from patients who had previously been treated at a conventional LINAC (mean age 71,[50 85years]) were analysed. Three patients with hip prostheses were excluded, leaving a total of 57 prostate and 28 prostatectomy patients. Two dosimetrists contoured the prostate (if present), bladder, rectum, small bowel, femoral heads, pelvic bones and external contour of the patients. If patient had fiducials or gold seeds, these were contoured separately. Mean ED value was obtained for each contour. For each organ, the maximum, minimum and average ED values and their SDs were analysed. In CTs with outlying organ EDs, a prostate dosimetry was performed according to the centre's protocols with its own ED; the same dosimetry was calculated on the ED values obtained in the first part of the study, analysing the dosimetric difference. Keywords: conformity, quality metrics, multiple dose levels