ESTRO 2025 - Abstract Book

S2894

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

ESTRO 2025

resources and enhancing consistency across patient plans, this tool represents a valuable step forward in radiotherapy automation.

Keywords: Automation, Auto-Planning, Eclipse Scripting API

References: [1] Cavus H, Rondagh T Jankelevitch A Tournel K Marc Orlandini M Bulens P Optimizing volumetric modulated arc therapy prostate planning using an automated Fine-Tuning process through dynamic adjustment of optimization parameters. Phys Imaging Radiat Oncol 2024;31:100619. https://doi.org/10.1016/j.phro.2024.100619 [2] Younge KC, Matuszak MM, Moran JM, McShan DL, Fraass BA, Roberts DA. Penalization of aperture complexity in inversely planned volumetric modulated arc therapy. Med Phys 2012;39:7160-70. https://doi: 10.1118/1.4762566.

3741

Mini-Oral Multicenter study on dose distribution variability in breast cancer radiotherapy Jan Seppälä 1 , Mikko Tenhunen 2 , Tuomas Koivumäki 3 , Jaana Mäkitalo 4,5 , Jukka Pyykkönen 6 , Erna Kaleva 6 , Tapio Ollonqvist 7 , Jar Vanhanen 8 , Eeva Boman 9,10 , Henna Hietala 11 1 Center of Oncology, Kuopio University Hospital, Kuopio, Finland. 2 HUS Comprehensive Cancer Centre, HUS, Helsinki, Finland. 3 Department of Medical Physics, Hospital Nova of Central Finland, Wellbeing Services County of Central Finland, Jyväskylä, Finland. 4 Department of Medical Physics, Turku University Hospital, Turku, Finland. 5 Department of Oncology, Turku University Hospital, Turku, Finland. 6 Helsinki University Hospital Cancer Centre, Radiation Therapy Unit of Lahti, Lahti, Finland. 7 Radiation Therapy Unit of Pori, Satasairaala, Pori, Finland. 8 Department of Oncology, South Karelia Central Hospital, Lappeenranta, Finland. 9 Department of Medical Physics, Tampere University Hospital, Wellbeing Services County of Pirkanmaa, Tampere, Finland. 10 Department of Oncology, Tampere University Hospital, Wellbeing Services County of Pirkanmaa, Tampere, Finland. 11 Department of Oncology and Radiotherapy, Oulu University Hospital, Oulu, Finland Purpose/Objective: Breast cancer is the most common cancer among women, with approximately 5000 new cases diagnosed annually in Finland. This study aimed to evaluate the consistency of dose distributions for a left-sided breast cancer patient with lymph node involvement across nine radiotherapy centers within the framework of the national harmonization initiative for radiotherapy treatments. Material/Methods: Nine radiotherapy centers participated in this study, generating a treatment plan for the same left-sided breast cancer case. Planning target volumes (PTVs) and treatment plans were created independently in each center following international and departmental guidelines. The prescription dose was 15×2,67 Gy totaling 40,05 Gy. The resulting PTV volumes, dose distributions, and organ-at-risk (OAR) doses were compared across centers, with a particular focus on doses to the heart and lung, as well as the extent of low-dose spillage. Results: The PTV volumes varied between 511 cm³ and 736 cm³, corresponding a 36% percentage difference (SD 75cm³). The 95% dose coverage of the prescription dose (D95%) averaged 93,5% (SD 2,0%). Treatment techniques included VMAT (n=4), IMRT (n=3), and 3D-CRT (n=2). Substantial variability was observed in OAR doses and low-dose spillage, as shown in Table 1 and Figure 1. For example, the volume receiving 5 Gy (V5Gy) ranged from 2346 cm³ to 4796 cm³ (SD 1500cm³), and the mean dose to the contralateral breast ranged from 0,3 Gy to 6,7 Gy. Variability was