ESTRO 2025 - Abstract Book

S4351

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Purpose/Objective: The aim of this study was to compare the doses delivered to humeral heads in breast cancer radiotherapy using 3D conformal radiotherapy (3D-CRT) versus VMAT techniques, and to analyse humeral head’s exposure with regards to irradiated target volumes. Material/Methods: A comparative dosimetric study including 64 consecutive breast cancer patients referred for adjuvant radiotherapy, was performed. All patients were planned hypofractionated radiotherapy with a prescription dose of 40 Gy/15 fractions +/- an additional boost to the tumor bed/thoracic wall. The ipsilateral humeral heads were delineated. For each patient, two treatment plans were generated using 3D-CRT and VMAT techniques. Both plans met target volume coverage and OAR dose constraints. Dose-volume histograms were generated. Dosimetry metrics to ipsilateral humeral head, including V5Gy, V10Gy, V30Gy, V40Gy, Dmean and Dmax, were analysed with regards to target volumes and statistically compared between both plans, using the t student test. Results: The mean age was 54.2 years. Thirty-six patients underwent radical mastectomy and 28 underwent breast conserving surgery. Tumor bed boost was prescribed in 37.5% of cases. Regional lymph nodes irradiation was performed in 81.3% of cases. Internal mammary chain was irradiated for 14.1% of patients. The mean Dmean/Dmax to humeral head were 1.67 Gy/13.82 Gy versus 3.2 Gy/11.66 Gy (p<0.00), respectively for 3D-CRT versus VMAT plans. The V5Gy/V10Gy were significantly higher in VMAT plans compared to 3D-CRT plans, with mean values of 21.34%/5.57% versus 3.85%/1.98% (p<0.001), respectively. No significant difference was found between the two techniques in terms of V20Gy, V30Gy, and V40Gy (all p>0.05). Axillary irradiation significantly increased doses to humeral head only in 3D-CRT plans (Dmean=7.22Gy versus 1.47Gy, p<0.001). No significant difference was found between VMAT plans with versus without axillary irradiation, in terms of humeral head doses. The Dmax to humeral head was significantly higher in case of level3/level4 lymph node irradiation, in both 3D-CRT and VMAT plans. Tumor bed boost did not significantly correlate with doses delivered to humeral head. Conclusion: Humeral heads irradiation in breast cancer radiotherapy was low. Compared to 3D-CRT, VMAT technique better spared humeral heads in case of axillary irradiation, but was related to higher low-dose volumes. Future studies are still needed to evaluate the impact of humeral heads low-dose exposure on shoulder morbidity and to establish specific dose constraints to humeral heads.

Keywords: Breast radiotherapy; humeral head, VMAT

2272

Digital Poster Integration and governance of MIM software in a multi-site institution. Craig Norvill Shenton House, GenesisCare, Perth, Australia

Purpose/Objective: We present an overview of how MIM software (Cleveland, OH) has been integrated into a large multi-site organisation, GenesisCare (GC), Australia consisting of 45 independent centers across five regulatory state authorities. This presents unique challenges and opportunities in the domain of system scalability, automated workflow and system administration. The multi-site nature of our organisation necessitates a consistent and automated approach to patient data operations and structure naming convention, allowing for seamless integration with nationally aligned treatment planning templates.