Temporal changes in native and late gadolinium enhanced ultrashort echo time magnetic resonance imaging during gynecologic cancer radiation therapy.

Background and purpose: Radiotherapy (RT) response in gynecologic cancers varies widely and is influenced by several factors. We evaluated whether fibrosis detected with inversion-recovery ultrashort-echo-time (IR-UTE) MRI (magnetic-resonance-imaging) signal-intensity (SI) could serve as noninvasive biomarkers of treatment response in patients imaged serially during external-beam RT (EBRT) and brachytherapy (BT). Materials and methods: Patients: Fifteen patients with gynecologic cancer were included. Five participants underwent seven MRIs: pre-RT, weeks 1 (RTwk1), 2 (RTwk2), and 3 (RTwk3) of EBRT, post-EBRT, 1-week post-BT, and 12 weeks post-BT. Ten participants did not receive MRI in RTwk1, RTwk2, or 1-week post-BT. Imaging: T2-weighted, diffusion-weighted images, and dynamic-contrast-enhanced MR images were acquired to segment the remnant-tumor-volume. Diffuse-fibrosis (FDiffuse) was imaged with non-contrast dual-echo IR research application, only retaining the ultrashort-(50 µs)-echo SI. Dense-fibrosis (FDense) imaging utilized Late-Gadolinium-Enhanced IR-UTE, acquired ∼ 15 min post-Gadavist. Analysis: R2* (apparent transverse relaxation rate) maps, indicative of hypoxia, were generated using R2* MRI. The mean FDiffuse SI, FDense SI, and R2* within the remnant-tumor-volume were determined and compared over the course of RT. Results: Changes in FDiffuse SI and FDense SI were observed after 14 Gy. Across all patients, FDiffuse SI peaked during RTwk2 and FDense SI peaked during RTwk3. FDense SI was higher during RTwk3 than pre-RT (p < 0.05). Minor changes in FDense SI were observed post-BT week-12 (p > 0.05). Remnant-tumor R2* correlated with FDense SI (p = 0.03). Conclusions: The largest increase in FDense occurred early during EBRT. Elevated FDense correlated with elevated R2* in the remnant-tumor, suggesting that fibrosis is an early indicator of radiation-resistant hypoxic regions.