Diffusion-weighted MRI in image-guided adaptive brachytherapy: Tumor delineation feasibility study and comparison with GEC-ESTRO guidelines

Purpose To examine the feasibility of using diffusion-weighted images (DWIs) coregistered with T2-weighted (T2w) sequence in treatment planning system to improve target delineation for image-guided adaptive brachytherapy (IGABT) in locally advanced cervical cancer patients. Methods and Materials We retrospectively examined the records of consecutive patients who were referred to our institution for pulse-dose-rate IGABT between May and December 2015 after concurrent chemoradiation. An MRI with T2w and DWI sequences with a maximum diffusion factor of 1000 s/mm² on a 1.5 or 3.0-T MR scanner was performed after placement of the vaginal mold applicator. T2w defined gross tumor volume (GTV_T2) and diffusion volume on DWI sequences (CTV_DWI) were retrospectively delineated, if achievable, by radiologist and radiation oncologist. Concordances between CTV_DWI and GTV_T2, high-risk and intermediate-risk clinical target volumes (CTV_HR and CTV_IR) were evaluated. Results Forty-four patients were identified: 23 patients (52%) had a GTV_T2 delineated, CTV_DWI was delineated in 42 patients (95%). Intraobserver and interobserver conformity indexes were <0.75 in 11 patients (26%) and 23 patients (54%), respectively. There was a positive correlation between GTV_T2 and CTV_DWI volumes (p = 0.038, r = 0.58). Median CTV_HR and CTV_DWI D₉₀ were 37.3 Gy (17.1–48.9 Gy) and 33 Gy (22–97 Gy), respectively (p = 0.659). CTV_DWI could have pointed CTV_HR delineation modifications in a total of 32 of 44 (73%) patients with CTV_DWI/CTV_HR conformity < 1. CTV_DWI volume was totally encompassed by CTV_IR in all patients. Conclusions These results suggest that DWI images as anatomical sequence without apparent diffusion coefficient mapping might have led to CTV_HR modifications. Still, interobserver and intraobserver variations in delineation are substantial, and artifacts make it difficult to implement.