Early outcomes and impact of a hybrid IC/IS applicator for a new MRI-based cervical brachytherapy program.

PURPOSE: The purpose of this study was to report early outcomes and assess the learning curve in a new MRI-based cervical brachytherapy program. METHODS: We accrued 33 patients prospectively, and only patients with ≥3 months' followup (n = 27) were assessed for disease control and toxicity. Eras were defined as first half and second half for the intracavitary (IC)-only era (n = 13 each), and the intracavitary/interstitial (IC/IS) era was separated by difference in applicator availability (n = 7). Dose to 90% of the high-risk clinical target volume (D90 HR-CTV) and minimum dose to the maximally irradiated 2 cubic centimeters (D2cc) to organs at risk were used to assess dosimetry. Statistics were performed with t tests and Kaplan-Meier method. RESULTS: Median followup was 14.7 months. Median treatment duration was 50.5 vs. 57 days for patients treated with external beam radiation therapy at our institution vs. an outside institution (p = 0.03). One-year local control, noncervical pelvic control, distant metastasis-free rate, and overall survival were 84.0%, 96.0%, 78.5%, and 91.3%, respectively. When comparing the first half and second half eras of IC only, there were no differences in median D90 HR-CTV or D2cc of the bladder, rectum, or sigmoid. Comparing the entire IC era to the IC/IS era, median D90 HR-CTV trended higher from 88.0 Gy to 92.9 Gy (p = 0.11). D2cc rectum decreased from 69.3 Gy to 62.6 Gy (p = 0.01), and D2cc bladder trended lower from 87.5 Gy to 83.6 Gy (p = 0.09). CONCLUSIONS: There was no significant difference between the first half and second half eras with IC-only MRI-based brachytherapy. Incorporation of an IC/IS applicator generated the greatest dosimetric improvement. Early results of the MRI-based brachytherapy program are favorable.