Oncentra external beam

GTVs were manually delineated via a standardized consensus method between the operators. Specifically, the ADC was overlaid with a constant false-colour lookup table over the 1100 s/mm 2 image. Some anatomical details were visible in the latter, and using these as a guide, an outline of the hyper-intense ADC region inside and adjoining the rectum was then drawn in by hand. On the THUNDER cohort, three observers, working independently, delineated the tumour on a Mirada (Mirada Medical, Oxford, UK) workstation. In the CLINIC cohort, two observers, working independently, delineated the tumour on an Oncentra External Beam (Elekta AB, Stockholm, Sweden) workstation. One common observer (author AT) delineated on both THUNDER and CLINIC cohorts. Observers (median experience, 4 years; range 1-10) were trained by a resident radiation oncologist to identify relevant normal and abnormal anatomical structures within the ADC maps. In addition, original CT scans with annotated lesions for all the patients were available to the observers, so that they could be guided in the delineations in the ADC maps. The median DICE for both the cohorts was 0.75 (range 0.6-0.90). At the end, delineations were exported into a single DICOM RT Structure Set file per patient. Each patient's ADC map was also exported in standard DICOM format.