CT versus MRI for Image-Guided Brachytherapy in Locally Advanced Cervical Cancer: A Propensity Score-Matched Analysis

Although MRI is the gold standard for image-guided brachytherapy for cervix cancer, CT scan is widely used. However, there is a dearth of comparative evidence.

Patients with FIGO (2018) stage IB3-IVA treated with (chemo)radiation and CT-ultrasound or MRI-based image-guided brachytherapy from 2016 to 2023 were included. The planning aim was to achieve D90 of ≥ 85 Gy₁₀ to high-risk clinical target volume and ≤90 Gy₃, ≤75 Gy_3, and ≤75 Gy equivalent dose in 2 Gy (EQD2) to 2cc bladder, rectum, and sigmoid, respectively. Propensity score matching was performed to compare local control, disease-free survival, and adverse events. Univariate and multivariable analyses were performed using the log-rank test and the Cox regression model. Post hoc power analysis was performed for noninferiority margin of 5%, assuming α = .15.

Of the 689 patients, 240 were eligible for propensity score matching (120 each in CT and MRI cohorts). Median high-risk clinical target volume was 34 cc (IQR, 26-42). Forty-three percent (n = 104) of patients underwent intracavitary-interstitial brachytherapy (IC-ISBT), whereas others received ICBT. At a median follow-up of 35.3 months, there was no difference in 3-year local control and disease-free survival between CT and MRI cohorts (local control, 89% [95% CI, 82%-97%] vs 92% [95% CI, 87%-97%], P = .71; disease-free survival, 71% [95% CI, 62%-82%] vs 73% [95% CI, 65%-81%], P = .86; respectively). Late grade ≥3 gastrointestinal and genitourinary toxicities were comparable ([8.2% vs 11%, P = .51] and [2.5 vs 4.2%, P = .49]). The hazard ratio for noninferiority of CT was 0.84 (95% CI, 0.34-2.07) with power of 0.69.

CT-based brachytherapy may provide comparable outcomes to MRI-based BT. The results of the study should be considered hypothesis-generating needing validation in prospective studies.