ESTRO 2024 - Abstract Book

S43 ESTRO 2024 As a consequence of the marked survival differences separate treatment strategies dependent on HPV/p16-status have been in focus for more than a decade. In the group of patients with HPV-related OPSCC, high disease control rates and a long life-expectancy have stimulated the design of de-intensified treatment schedules aiming at avoiding excess toxicity and long-term morbidity without compromising outcome. However, early attempts, substituting cisplatin with EGFR-inhibitor, resulted in higher locoregional failure and worse survival without improvement in toxicity in three phase III randomized trials. Thus, selecting patients for treatment deintensification requires caution, and cisplatin-based CRT remains the standard of care for advanced HPV-positive OPSCC. In HPV-negative OPSCC, the challenge is typically somewhat different, as these patients with poor prognosis, who need aggressive treatment, often suffer from pronounced co-morbidities and poor performance status, with consequent difficulties in complying with the intensive therapy. Consequently, patients with HPV-negative disease continue to represent a therapeutic challenge. The talk will cover the epidemiological development in OPSCC over the past 35 years exemplified by the nationwide DAHANCA cohort study of more than 8000 patients. Outcome in relation to tumour p16-status and radiobiological treatment intensification, including subsite differences (BOT/tonsil vs other oropharyngeal subsites), along with the impact of smoking and co-morbidity will be discussed. A discussion of possible ways to intensify treatment in order to improve outcome in poor prognosis patients will be provided based on data from meta-analysis and clinical studies, including hyperfractionated accelerated RT with dose escalation in patients with advanced disease who are unfit for chemotherapy and hyperfrationated RT combined with chemotherapy in patients with good performance and limited co-morbidity. Invited Speaker

3351

Hypofractionation: What are the implications with regard to image guidance and accuracy?

Paul J Keall

University of Sydney, Image X Institute, Sydney, Australia

Abstract:

A 2024 Lancet Oncology paper states that hypofractionation – which must be based on careful technological and dosimetric QA protocols – may reduce overall treatment time, shorten wait lists, strengthen radiation therapy access, increase system capacities, and reduce both the direct and indirect costs of treatment. Guidance on the accuracy requirements for hypofractionation written by the AAPM Task Group 101 and published 14 years ago still rings true today: In order to minimize the normal tissue toxicity, conformation of high doses to the target and rapid fall-off doses away from the target is critical. The practice of SBRT therefore requires a high level of confidence in the accuracy of the entire treatment delivery process. In SBRT, confidence in this accuracy is accomplished by the integration of modern imaging, simulation, treatment planning, and delivery technologies into all phases of the treatment process. Hypofractionation has sources of uncertainty up to treatment planning, including imaging errors due to motion and contour delineation variations, that limit the accuracy. Once a plan is created, the main source of uncertainty comes from patient anatomic changes, as evidenced by end-to-end dosimetry studies and online and real-time adaptive radiation therapy clinical studies.