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/mm 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) and diffusion volume on DWI sequences (CTV) were retrospectively delineated, if achievable, by radiologist and radiation oncologist. Concordances between CTV and GTV, high-risk and intermediate-risk clinical target volumes (CTV and CTV) were evaluated.

RESULTS

Forty-four patients were identified: 23 patients (52%) had a GTV delineated, CTV 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 and CTV volumes (p = 0.038, r = 0.58). Median CTV and CTVD were 37.3 Gy (17.1-48.9 Gy) and 33 Gy (22-97 Gy), respectively (p = 0.659). CTV could have pointed CTV delineation modifications in a total of 32 of 44 (73%) patients with CTV/CTV conformity < 1. CTV volume was totally encompassed by CTV in all patients.

CONCLUSIONS

These results suggest that DWI images as anatomical sequence without apparent diffusion coefficient mapping might have led to CTV modifications. Still, interobserver and intraobserver variations in delineation are substantial, and artifacts make it difficult to implement.