Single-Institution Experience in 3D MRI-Based Brachytherapy for Cervical Cancer for 239 Women: Can Dose Overcome Poor Response?

Purpose: Recent Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology guidelines recommend that the dose to 90% (D90) of the high-risk clinical target volume (HRCTV) in cervical cancer be at least 85 Gy, with higher doses for poor response to radiation therapy.
Methods and Materials: A retrospective review of brachytherapy delivered at a single institution was evaluated for dosimetry and outcomes. Significance of tumor parameters on local control was evaluated with Kaplan-Meier and univariable and multivariable Cox regression analysis. Correlations were determined with a linear regression model.
Results: A total of 239 women underwent high-dose-rate brachytherapy for cervical cancer between 2007 and 2018 with evaluable dosimetry. Median follow-up was 28.6 months. The median prescribed dose was 27.5 Gy in 5 fractions, with a median HRCTV D90 of 83.9 Gy (range, 81.9-85.7 Gy), HRCTV volume of 31 cm ³ (range, 14.9-121.9 cm ³ ), and treatment time of 51 days (range, 36-83 days). Local control for the entire cohort at 5 years was 90.8%. Local control was worse with adenocarcinomas, HRCTV >40 cm ³ at brachytherapy, requirement for a higher brachytherapy dose, and treatment >51 days. On multivariable analysis, local control was worse with adenocarcinoma (hazard ratio, 4.141; 95% confidence interval, 1.498-11.444; P = .006) and HRCTV >40 cm ³ (hazard ratio, 3.640; 95% confidence interval, 1.316-10.069; P = .013). HRCTV EQD2 D90 > 85 Gy did not statistically improve outcomes for any subset. The 2-year progression-free survival for HRCTV >40 cm ³ was 66.2% versus 84.1% if ≤40 cm ³  (P < .001). Overall survival was predicted by HRCTV and overall treatment time in multivariable analysis. For women with HRCTV ≤40 cm ³ , overall survival at 2 years was 90.4% versus 68.5% if >40 cm ³  (P < .001).
Conclusion: Local control was excellent with magnetic resonance imaging-based planning in the entire cohort of patients. A poor response to external beam radiation (larger HRCTV) and adenocarcinoma histology predicted for worse local control despite association with higher brachytherapy prescription. Women with these risk factors face higher rates of extrapelvic progression and poorer overall survival.
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