Chemoradiotherapy treatment
toxicity, tumour, ®
TUMOUR, RECTAL CANCER
All eligible patients were referred for nCRT by 0.35 T MRIgRT using MRIdian® Linac (ViewRay Inc, USA) system. The technical details of the treatment procedures have already been described in our earlier work on the study design [The GTV was contoured and independently checked by another experienced radiation oncologist in the field of rectal cancer on the MRI of the simulation and of the 10th therapy fraction for the calculation of the ERI index according to the following formula [
where Vpre is the GTV measured at the time of simulation and Vmid is the volume measured during therapy, at 10th fraction. GTV was defined as the primary rectal tumour seen on MRI scans taken during MRgRT treatment, including information obtained from diagnostic MRI scans. Patients with an ERI < 13 continued with the treatment planned at baseline. Patients with an ERI ≥ 13, classified as “non-responders”, underwent replanning. In the latter case, SIB3 treatment was replanned from the 11th session, aiming to increase the dose up to 60.1 Gy with daily fractionation of 2.54 Gy to PTV3, obtained by GTV + 0.3 cm isotropic margin.In order to avoid any treatment-related toxicity and to exploit the potential of the MRIgRT technology, treatment in these cases was delivered using an OA strategy.The dose was delivered using a cine-MRI gating protocol with a 5% region of interest (ROI) set within a 5 mm boundary from the CTV2 or 3 mm at the GTV in the case of dose escalation. This ensured the target volumes to be consistently positioned as planned during the procedure.Five cycles of concurrent fluoropyrimidine-based CHT with 5-FU (225 mg/m