Author: Diandra Ayala-Peacock, Junzo Chino, Oana I. Craciunescu, Allison Jones, Kyle J. Lafata, Kim Light, Sheridan G. Meltsner, Jack B Stevens 👨🔬
Affiliation: Duke University, Department of Radiation Oncology, Duke University, Duke University Medical Center 🌍
Purpose: This study aims to develop an MR-based method that retrospectively correlates longitudinal changes in morphology and physiology for the bulboclitoris and vaginal canal with dose received during external-beam radiation therapy (EBRT).
Methods: Patients treated with EBRT under an IRB approved protocol for pelvic malignancies were included. Longitudinal changes were evaluated using pre-treatment (pX) and pre-brachytherapy (pBT) T2w-MRIs and diffusion weighted images (DWI, b=1000), acquired 3-4 weeks apart on a 3T Siemens MAGNETOM Skyra scanner. The bulboclitoris and vaginal canal were manually contoured on T2w-MRI at both time points. A MIM workflow (MIM Software Inc.) was created to analyze morphological changes - volume and Dice Similarity Coefficients (DSC)- and signal changes in DWI values. For the latter, regions of interest (ROIs) were analyzed on both pX and pBT DWI to measure changes in median signal. ROIs were based on the 20, 30, and 40 Gy isodose lines determined by deformable registration of T2w-MRI to planning CT. Change in DWI was split into low and high dose groups based on ROI dose (>40Gy vs. <40 Gy vaginal canal, 20 Gy vs. 40 Gy bulboclitoris).
Results: Due to availability, data from 16 patients (bulboclitoris) and 9 patients (vaginal canal) were analyzed. Larger volume reductions were seen at higher doses (vaginal canal: 32.3% vs. -25.9%, bulboclitoris: 19.4% vs. 3.2%), and DSC values were lower at higher doses (vaginal canal: 0.58 vs. 0.51, bulboclitoris: 0.72 vs. 0.66). Higher increase in DWI signal was observed in the high-dose group (vaginal canal: 55.3% vs. 30.3%, bulboclitoris: 123.3% vs. 44.8%), meaning greater diffusion restriction and physiologic change occurs at higher doses.
Conclusion: This proposed image-based method identifies preliminary dose thresholds for morphological and physiological changes in the bulboclitoris and vaginal canal and may inform the design of prospective studies on sexual dysfunction in GYN cancer patients post-EBRT.