ESTRO 2024 - Abstract Book

S4019

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

[1] Houweling AC, van der Meer S, van der Wal E, Terhaard CH, and Raaijmakers CP. Improved immobilization using an individual head support in head and neck cancer patients. Radiother Oncol, 96:100–103, 7 2010.

1210

Poster Discussion

Dose tracking in Head and Neck cancer - possible benefits with Adaptive Radiotherapy

Hedda Enocson 1,2 , André Haraldsson 1,2 , Per Engström 1 , Sofie Ceberg 2 , Maria Gebre-Medhin 3,4 , Gabriel Adrian 3,4 , Per Munck af Rosenschold 1,2 1 Radiation Physics, Department of Hematology, Oncology, and Radiation Physics,Skåne University Hospital, Lund, Sweden. 2 Medical Radiation Physics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 3 Oncology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden. 4 Oncology, Department of Hematology, Oncology, and Radiation Physics,Skåne University Hospital, Lund, Sweden

Purpose/Objective:

Adaptive radiation therapy (ART) is a method for continuous adjustment of treatment based on anatomical or biological changes. Previous studies on head and neck squamous cell carcinoma (HNSCC) radiotherapy have reported a reduction in treated volumes, as demonstrated by Morgan et al. (2020) and suggested that adaptations are often influenced by weight loss, with intervention commonly occurring around the 15-17 fraction (Figen M et al., 2020; Tejpal Gupta et al., 2023). These findings suggest the use of an offline-ART approach in HNSCC treatment. Mislav Bobić et al. (2022) reported that weekly ART might be a comparable alternative to daily adaptations with respect to clinical target volume (CTV) coverage and organ-at-risk (OAR) dose. Most studies have however kept the PTV margins and studied potential improvements in dose coverage of the PTV using ART. The purpose of this study was to retrospectively assess the advantages and feasibility of ART for HNSCC by reducing the PTV margins and evaluate the dosimetric impact. A total of 31 HNSCC patients (895 treatment fractions) were retrospectively studied, all previously treated at our center with helical Tomotherapy on a CT-linac (Radixact®, Accuray, Madison, WI). The patients were prescribed 60.0-68.0 Gy, in 2 Gy/fraction with SIB to nodal volumes, using a 5 mm CTV-PTV margin, and imaged with daily kVCT. Additional plans with 2 mm CTV-PTV margin were generated and studied. A synthetic CT was generated from daily kVCT images with a deformable registration (RayStation 2023B, RaySearch Laboratories, Stockholm) between the planning CT and the kVCT. A deformable image registration method was used to propagate the GTV/CTV as well as OAR onto the daily kVCT. The delivered dose was calculated on the synthetic kVCT images, and the total delivered dose was accumulated from all treatment fractions, for the 5mm and the 2mm plans respectively. Adapted plans were generated from the 5mm plan for each fraction, optimized based on the daily deformed structures. To evaluate the necessity of adaptation to Material/Methods: