ESTRO 2024 - Abstract Book

S5123

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2024

2458

Digital Poster

feasibility of oxygen-enhanced MRI measurement in the whole prostate on an MR-Linac

Chris Moore 1,2 , Martin Swinton 1,2 , Eliana Vasquez Osorio 1 , Damien McHugh 1,2 , Robert Bristow 1,3 , Marcel van Herk 1 , Ananya Choudhury 1,3 , David L Buckley 4 , Ashwin Sachdeva 5,1 , Noel Clarke 5 , Jeremy Oates 5 , Michael J Dubec 1,2 1 University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom. 2 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom. 3 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom. 4 University of Leeds, Biomedical Imaging, Leeds, United Kingdom. 5 The Christie NHS Foundation Trust, Urology, Manchester, United Kingdom

Purpose/Objective:

The purpose of this work was to assess the feasibility of using Oxygen Enhanced MRI (OE-MRI) (1) to obtain oxygen sensitive T1-related signal changes in the whole prostate in treatment naïve patients with prostate cancer on an MR Linac (2). Molecular Oxygen is paramagnetic, and therefore increased oxygen concentration increases the signal intensity in T1-weighted images, when present in solution in blood plasma and interstitial fluid as it induces increased T1 relaxation (1). After increased oxygen uptake an excess of dissolved oxygen builds up. In hypoxic tissue this excess dissolved oxygen is taken up by cells and therefore no signal increase occurs; whereas in normoxic tissue, the cells are saturated with oxygen, so the excess oxygen remains in solution to produce the signal enhancing effect. Increased tumour hypoxia is linked to increased treatment resistance and OE-MRI is being investigated for use as an imaging biomarker of tumour hypoxia (3,4). Previous studies have shown the feasibility of OE-MRI in head and neck cancer on an MRI Linac (1).

Material/Methods:

Seven patients with localised prostate cancer recruited in the Hyprogen trial (NCT05702619) were imaged on an Elekta Unity MR-Linac with a T2-weighted fast spin-echo (FSE) and a dynamic T1-Weighted inversion recovery turbo field echo sequence (IRTFE) (resolution = 3 x 3 x 2.5 mm, inversion delay = 1100 ms, echo-time = 1.1 ms, repetition time = 3.2 ms temporal resolution = 12 s, 75 time points). Five patients were imaged once on the MR-Linac and two patients were imaged twice, for a total of nine patient visits. Patients were imaged while wearing a medical gas mask which could deliver varying concentrations of oxygen. While the dynamic sequence was running the gas was switched from 21% oxygen (air) to 100% oxygen at time point T = 21, and back to 21% oxygen (air) at time point T = 61.