ESTRO 2022 - Abstract Book

S945

Abstract book

ESTRO 2022

This study aims to investigate the feasibility of performing R2* and Intra-Voxel Incoherent Motion (IVIM) sequences on the MRL to evaluate longitudinal changes of hypoxic and perfusion parameters over a course of radiotherapy in patients with HNC. Materials and Methods Four patients with stage III (TNM 8th edition) p16-positive oropharyngeal squamous cell carcinomas received radical radiotherapy to 65 Gy in 30 fractions to the primary target and involved nodes. Patients were scanned with radial multi- echo gradient-echo and diffusion-weighted MRI sequences on the MRL at baseline pre-radiotherapy and once weekly during radiotherapy. R2* maps were generated in MATLAB by calculating the linear regression of the natural log of signal intensities from the multi-echo images, on a voxel-by-voxel basis. Perfusion maps from the diffusion-weighted sequences (b0, 30, 150 and 500 s/mm ² ) were generated in MATLAB. RayStation treatment planning system was used for Dicom analyses. R2* and perfusion maps were fused with T2-weighted MRIs. Primary targets and involved nodes were contoured by a radiation oncologist and histograms were generated to derive voxel-wise data. Contralateral parotid glands were used as controls and to normalise R2* data. Hypoxic voxels were defined as R2* above 60 s ‾¹ . “Hypoperfusion fraction” was defined as the total voxel volume of perfusion fractions between 0-15%. Results Table 1 displays the hypoxic and perfusion fractions of the primary and involved lymph nodes. An example R2* image for patient 1 is shown in Figure 1. Patients 2 and 4 had complete resolutions of primary tumours during radiotherapy with complete responses on post- treatment FDG PET/CTs. Patients 1 and 3 had increases in hypoxic fractions towards the end of treatment and both had residual avidity on post-treatment PET/CT scans attributed to inflammation. Patient 3 had a large increase in hypoperfusion fraction of the primary (296%). Patients 1, 2 and 4 saw reductions in the hypoperfusion fractions during radiotherapy. In lymph nodes, Patients 1 and 3 had increases in hypoxic fractions towards the end of treatment. Hypoperfusion fractions increased in patients 1 and 3. The largest increase in hypoperfusion fraction was in patient 3 (71.4%).