ESTRO 2025 - Abstract Book

S113

Invited Speaker

ESTRO 2025

6. Zaghloul MS, Christodouleas JP, Smith A et al. Adjuvant sandwich chemotherapy plus radiotherapy vs adjuvant chemotherapy alone for locally advanced bladder cancer after radical cystectomy. A randomized phase II trial. JAMA Surgery 2018; 153: e174591 7. Fonteyne V, Dirix P, Van Praet C, et al. Adjuvant radiotherapy after radical cystectomy for patients with high-risk muscle-invasive bladder cancer: results of a multicentric phase II trial. Eur Urol Focus 2022; 8: 1238-1245. 8. Verghote F, Sargos P, Christodouleas JP, et al. International Consensus Guidelines for adjuvant radiotherapy for bladder cancer after radical cystectomy: update from an IBIS workgroup. Pract Radiat Oncol 2022; 6: 524-532. 9. Murthy V, Maitre P, Singh M, et al. Study protocol of the bladder adjuvant radiotherapy (BART) trial: a randomized phase III trial of adjuvant radiotherapy following cystectomy in bladder cancer. Clin Oncol (R Coll radiol) 2023; 35:e506-e515. Doi: 10.16/j.clon.2023.04.010

4835

Speaker Abstracts We are more than ready: We are wasting our time

Robert Jeraj 1,2 , Vincent Gregoire 3 , Luciano Rivetti 1 , Ilamparithi Balasubramanian 1 , Thomas Bortfeld 4 , Arturo Chiti 5 , Uulke van der Heide 6 , Cynthia Menard 7 , Edmond Sterpin 8 , Daniela Thorwarth 9 , Brian O'Sulivan 7 , Thomas Mackie 2 1 Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia. 2 Medical Physics, University of Wisconsin, Madison, USA. 3 Radiation Oncology, Leon Bernard Cancer Center, Lyon, France. 4 Radiation Oncology, Harvard Medical School, Boston, USA. 5 Nuclear Medicine, Ospedale San Raffaele, Milano, Italy. 6 Radiation Oncology, Netherlands Cancer Institute, Amsterdam, Netherlands. 7 Radiation Oncology, Centre Hospitalier de l`Université de Montréal, Montreal, Canada. 8 Institute of Experimental and Clinical Research, UC Louvain, Brussels, Belgium. 9 Radiation Oncology, University Hospital Tübingen, Tübingen, Germany Abstract: Since ICRU Report 50, conventional radiotherapy has enshrined the principle of prescribing a therapeutic dose to an enlarged margin-based Planning Target Volume (PTV) that encompasses both the traditional Gross Tumor Volume (GTV) and Clinical Target Volume (CTV), while trying to protect Organs at Risk (OAR) containing vulnerable radiation sensitive anatomy. However, within such apparently straightforward concepts, a myriad of uncertainties exists. They include identification of the location and characteristics of the GTV at a single point of assessment, but also perturbations in position and shape during a course of fractionated radiotherapy. Leaving aside whether the imaging used has captured the GTV adequately, there exists potential uncertainty about the extent and distribution of microscopic disease that defines the CTV as well as heterogeneity within the gross disease governed by numerous biological phenomena that in turn could vary throughout the treatment course. Similar uncertainties apply to normal anatomy although, in general, the main preoccupation has been the proximity to the high-dose target and important potential variations that may take place during treatment. Overall, it is acknowledged that the GTV-CTV-PTV paradigm introduced by a series of ICRU reports has been exceptionally helpful and allowed for simple and consistent planning, employing standardized dose prescription and reporting that greatly facilitated the development of higher quality dose-volume relationship data across and between institutions. However, this traditional formalism has oversimplified with contours alone the heterogeneity and complexity exhibited by tumors and the alterations that might exist regarding the protection of normal structures. Procedures that explicitly consider the influence of possible variations during the planning of radiation therapy treatments can yield plans that are more robust to deviations while delivering lower doses to normal tissues than margin-based plans. Robust optimization methods have emerged that may dispense with margins and instead more optimally account for patient anatomy change during and between fractions of radiotherapy. For example, it is conceivable that lower doses in some fractions could be compensated by employing higher doses in others.