2878 - Exploring the Use of Advanced DWI Techniques to Improve Prediction of Early Treatment Response during Definitive Chemoradiation for Cervical Cancer

Purpose/Objective(s): Apparent diffusion coefficient (ADC) from DW MRI have been shown to correlate with response to definitive chemoradiation for cervical cancer. Therefore, we explore the capability of advanced DWI techniques to further improve early treatment response predictions.

Materials/Methods: As part of an IRB-approved study, nine women undergoing chemoradiation for cervical carcinoma obtained MRIs at 7 timepoints (pre-treatment (1), weekly during RT (5) and 3-4 month post treatment (1) ). Two advanced DWI sequences: multi-shot EPI (msEPI) and multi-shot TSE (msTSE), were compared with conventional single-shot EPI (ssEPI). Rigid registration between the T2-weighted (T2w) and b=0 reference scan from each DWI sequence was performed. For all timepoints, a tumor contour based on the T2w scan (Tumor_T2), and tumor subvolumes for each sequence (SubVol_ssEPI, SubVol_msEPI, SubVol_msTSE) were delineated. Subvolumes were defined as hypointense regions on the ADC map and hyperintense regions on the high b value scan overlapping Tumor_T2. The mean ADC values and volume changes of all contours were extracted.

Results: Longitudinal decrease in tumor and subvolume sizes and diffusion signal were observed. Week 2 of RT was chosen for comparison as prior studies identified this timepoint as most indicative of early response. msTSE was noisier but had improved geometric integrity for contouring compared to ssEPI and msEPI, where increased signal pile-up and geometric distortion were seen in the presence of gas. The mean ADC values (average ± std across patient cohort) within Tumor_T2 at baseline on the msEPI, ssEPI and msTSE scans were (1.20±0.08, 0.94±0.10, 1.12±0.16) 10^-3 mm²/s, and the percent increase at week 2 were (20.6±13.2, 21.3±12.9, 18.8±15)%, respectively. This demonstrates that while the absolute ADC values vary between sequences, the change is consistent. The pretreatment volumes of Tumor_T2, SubVol_ssEPI, SubVol_msEPI, SubVol_msTSE were (66.3±53.4, 48.2±42.4, 42.6±36.3, 47.7±42.4) cc, and the percent decrease at week 2 of RT were (36.1±9.5, 46.6±20.6, 54.1±22.9, 49.5±19.9)%, respectively. Details are shown in Table 1.

Conclusion: Tumor volume delineation based on DWI sequences may be more sensitive at detecting true changes in residual disease than contours based on T2w anatomical imaging.