ESTRO 2025 - Abstract Book

S4341

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Conclusion: The evaluation of factors that triggered adaptive replanning was validated by the CTV dose coverage results evaluated on the re-CT scans. By protocolising the factors for treatment adaptation, it can mitigate redundant CT simulations and dependency on one’s discretion for replan because the processes are burdening to staff and resources. To benchmark to the traffic-light action protocol developed by the Netherlands Cancer Institute, we can adopt the guidelines and incorporate our departmental practices of plan adaptation criteria of proton therapy in a protocolised system in the future. References: Bohannon, D., Janopaul-Naylor, J., Rudra, S., Yang, X., Chang, C. W., Wang, Y., Ma, C., Patel, S. A., McDonald, M. W., & Zhou, J. (2023). Prediction of plan adaptation in head and neck cancer proton therapy using clinical, radiographic, and dosimetric features. Acta Oncol, 62(6), 627-634. https://doi.org/10.1080/0284186X.2023.2224050 van Beek, S., Jonker, M., Hamming-Vrieze, O., Al-Mamgani, A., Navran, A., Remeijer, P., & van de Kamer, J. B. (2019). Protocolised way to cope with anatomical changes in head & neck cancer during the course of radiotherapy. Tech Innov Patient Support Radiat Oncol, 12, 34-40. https://doi.org/10.1016/j.tipsro.2019.11.001 Digital Poster Implementation of Mid-Ventilation Stereotactic Ablative Body Radiotherapy (SABR) for Stage I Non-Small Cell Lung Carcinoma (NSCLC) Kendell Shields-Dowton 1 , Joel Poder 1,2,3 , Johnson Yuen 1,4,5 , Laurel Schmidt 1 , Jeffrey Barber 6,7 , Eric Hau 6,8,9 , Jonathon Lee 10 , Angela Rezo 10,11 , Yaw Sinn Chin 1,12 1 Department of Radiation Oncology, St George Cancer Care Centre, Kogarah, Australia. 2 Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia. 3 School of Physics, University of Sydney, Camperdown, Australia. 4 Medical Physics, Ingham Institute for Applied Medical Research, Sydney, Australia. 5 South Western Clinical School, University of New South Wales, Sydney, Australia. 6 Department of Radiation Oncology, Western Sydney Local Health District, Sydney, Australia. 7 Institute of Medical Physics, University of Sydney, Sydney, Australia. 8 Westmead Clinical School, University of Sydney, Sydney, Australia. 9 Centre for Cancer Research, Westmead Institute of Medical Research, Sydney, Australia. 10 Radiation Oncology Department, Canberra Region Cancer Service, Canberra, Australia. 11 College of Health and Medicine, Australian National University, Canberra, Australia. 12 St. George & Sutherland Clinical School, UNSW Medicine, Sydney, Australia Purpose/Objective: The Mid-Ventilation (MidV) method is an alternative to the Internal Target Volume (ITV) method for generating a Planning Target Volume (PTV) in lung stereotactic ablative radiotherapy (SABR). It potentially reduces damage to normal surrounding lung tissues whilst providing very high local control rates 1 . We retrospectively assessed translatability of a MidV workflow that was developed by our institution using the Eclipse (v15.6) treatment planning system (TPS) and Aria (v16.0) Oncology Information System in two other Australian Radiation Oncology (RO) departments and compared dosimetric parameters between both methods. Material/Methods: The initial MidV workflow was validated on 10 lung SABR patients at our institution. This workflow was introduced to two other lung sub-specialised RO’s. RO2 generated MidV PTV for patients 1-10 and RO3 for patients 11-20 respectively. RO1 then independently re-contoured and re-generated MidV PTV for all twenty patients. Each pair of these MidV volumes were compared, with those of RO1 considered as ground truth for the workflow. As there are no standardised methodologies for comparing inter-observer variability (IOV) 2 , several metrics were compared including MidV Phase selection, PTV margins, mean distance-to-agreement (MDA) and Dice Similarity Coefficient Keywords: proton, adaptive, dose evaluation 1759