ESTRO 2024 - Abstract Book

S4119

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

A total of 100 treatment fractions were evaluated, with the selection of full (28/100), normal (62/100), and empty (28/100) bladder plans.

The mean PTV percentage difference was found to be 10% (ranging from 0.2% to 18.0%) when comparing the PTV derived from the daily CBCT scans with the PTV from the three planning CT options (full, normal, and empty bladder).Moreover, the median value of PTV receiving the 95% of the prescription dose (V95%) was 90% (ranging from 85% to 97%) for the POD-ART plans. On the other hand, V95% achieved the median value of 98% in Ethos-ART fractions.

Ethos-ART total delivered dose showed a median decrease of 15% in bowel bag volume receiving 45 Gy (IQR: 12.7% to 27.9%) and 40% in rectum volume receiving 50Gy (IQR: 25% to 65%) compared to POD-ART workflow.

Conclusion:

Ethos-ART for bladder cancer radiotherapy exhibited significant reductions in treatment volumes and doses to Organs at Risk (OARs) compared to POD-ART, while maintaining effective target coverage. These findings suggest the potential for a reduction in gastrointestinal toxicities. Further investigations in a larger patient population are needed to consolidate our findings.

Keywords: bladder cancer, oART, Ethos emulator

3095

Digital Poster

Dose escalation to hypoxic volumes and offline adaptation for patients with head and neck cancer

Laura A Rechner 1 , Patrik Sibolt 1 , Christian Maare 1 , Camilla K Lonkvist 1 , Kristin Skougaard 2 , Henriette K Mortensen 1 , Raúl A Pérez 1 , Jens Edmund 1 1 Copenhagen University Hospital – Herlev and Gentofte, Department of Oncology, Copenhagen, Denmark. 2 Danish Medicines Agency, Centre for Medicines Licensing, Human Medicines, Oncology, Copenhagen, Denmark

Purpose/Objective:

Hypoxia reduces the efficacy of radiotherapy (RT) and is a negative prognostic factor for patients with head and neck (HN) cancer [1]. Dose escalation (DE) to the hypoxic volume (HV) within the gross tumor volume (GTV) is one strategy to combat this effect; however, data on the robustness of DE plans to anatomical changes throughout the treatment course with or without adaptation is limited. Additionally, mitigation of potential hot spots becomes imperative to prevent mucosal toxicity at escalated dose levels [2]. The purpose of this study was to investigate the impact of anatomical changes on both target coverage and dose to organs at risk (OARs) for plans with HV-based DE for patients with HN cancer. Offline adaptive as well as non-adaptive strategies were investigated.