Purpose: To evaluate the percentage of gynecological fibrosis using novel UTE methods pre-, during (33Gy)-, and post (45Gy)-radiotherapy.
Methods: Patients underwent whole pelvis irradiation using VMAT. MR images were acquired pre/during/post -EBRT on 1.5T scanner (Siemens Aera/Sola) using a prototype stack-of-spirals dual-echo, inversion-recovery IR-UTE sequence (TE1,2=50, 2690µs, resolution=1.0×1.0×2.5mm³). To evaluate acute (diffuse) fibrosis (Fᴬ), which has a short TE and T1, TI=60ms or 80ms, TE₂ images were subtracted from TE₁ images . Chronic fibrosis (Fᶜ), with the longest contrast uptake time, was evaluated using TE₁ of (late-gadolinium-enhancement) LGE-UTE, TI=200ms, acquired 10-13 min after contrast-injection. Images were registered to the simulation CT, and targets were propagated onto the MR images. UTE images were segmented using region-growing (RayStation 10A, Stockholm). Acute fibrosis (Fᴬ) and chronic fibrosis (Fᶜ) regions were segmented on the non-contrast STIR-UTE and on the LGE-UTE, respectively, and propagated onto T2w images. The contours were cropped to remain within the CTV contour. Percentages of the Fᴬ and Fᶜ within the CTV were determined and compared pre-, on- and post-EBRT using an ANOVA with repeated measures with a Greenhouse-Geisser correction.
Results: In seven gynecological patients treated with whole pelvis irradiation, pre-treatment, on-treatment, and post-treatment Fᴬ/Fᶜ were: 11±11%/5±2%, 19±8%/12±10%, and 34±15%/18±10%, respectively. The mean Fᴬ were statistically significantly different (F(1.97, 11.83) = 8.11, p < .01) across time points. Similarly, the mean Fᶜ were statistically significantly different (F(1.36, 8.17) = 7.64, p = .02) across all time points. Pairwise comparisons demonstrated that pre- and post-treatment Fᴬ and Fᶜ were significantly different (p=.03). Fᴬ and Fᶜ grew during radiotherapy, with Fᴬ converting to Fᶜ at later time-points.
Conclusion: In patients treated with pelvic VMAT, Fᴬ and Fᶜ increased over the course of radiation therapy. Identifying fibrosis progression offers a means to achieve response-driven adaptive radiotherapy, potentially leading to improved outcome with reduced toxicity.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institutes of Health under Grant No. R01CA237005.
Not Applicable / None Entered.