ESTRO 2024 - Abstract Book

S5000

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2024

Institution, 4-Dimensional Computed Tomography-Ventilation Functional Avoidance Prospective Clinical Trial," in Advances in Radiation Oncology, vol. 8, 2023.

859

Digital Poster

Intrafraction changes of DWI-based high-risk subvolumes in head and neck cancer

Jonas Habrich 1 , Simon Böke 2,3 , Cihan Gani 2,3 , Maximilian Niyazi 2,3 , Daniel Zips 2,4,5 , Daniela Thorwarth 1,3

1 Section for Biomedical Physics, Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany. 2 Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany. 3 German Cancer Consortium (DKTK), partner site Tübingen, and German Cancer Research Center (DKFZ), Heidelberg, Germany. 4 Charité - Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Department of Radiation Oncology, Berlin, Germany. 5 Charité - Universitätsmedizin Berlin, Berlin, Germany; German Cancer Consortium (DKTK), partner site Berlin, and German Cancer Research Center (DKFZ), Heidelberg, Germany

Purpose/Objective:

Biological information related to tissue heterogeneity and hypoxia in tumors is hypothesized to be the main causes of therapy failure in head-and-neck cancer (HNC). Therefore, quantitative imaging biomarkers (QIBs) measuring biological characteristics might enable biologically-based individualization of a patients´ radiotherapy. Previous studies have identified the apparent diffusion coefficient (ADC), calculated from diffusion-weighted magnetic resonance imaging (DW-MRI), as a prognostic QIB in the radiotherapy of HNC patients [1, 2] as well as a basis for the prediction of radioresistance in a preclinical study [3]. To overcome radioresistance, dose escalation to subvolumes inside the tumor, detected by segmented QIB maps were proposed previously [4]. Even though recent studies have investigated repeatability of mean ADC values in tumors [5, 6], no data on the consistency of ADC-based subvolumes is currently available which is a critical prerequisite for biologically adaptive RT based in QIBs. Therefore, the aim of this study was to assess intra-fraction changes of high-risk subvolumes (HRSs), determined by a band of ADC values, in HNC patients treated on the 1.5 T MR-Linac (MRL).

Material/Methods:

Eleven patients with locally advanced HNC were previously treated with 70 Gy in 35 fractions at the 1.5 T MRL. One to two times per week, an echo-planar DW sequence was acquired before the start of irradiation (Test) and during plan adaptation (Retest) within one treatment fraction with approximately 10 min in between. The DW sequence used TR/TE of 4811/68 ms, an acquisition voxel size of 3x3x4 mm3, a field-of-view of 400x400x100 mm3, Spectral Attenuated Inversion Recovery (SPAIR) for fat suppression and b-values (averages) of 0 (3), 150 (5) and 500 (8) s/mm2. All Retest images were rigidly registered to their corresponding Test images and gross tumor volumes (GTVs) were delineated by a radiation oncologist on both b-500 images separately. ADC maps were calculated using b-values of 150 and 500 s/mm2 and a pixel-wise mono-exponential fit. HRSs were determined as all voxels within the GTV and ADC values between 600 – 900 × 10-6mm2/s. Additionally, a closing filter was applied. Volumes of filtered and