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

The purpose of this study was to report early outcomes and assess the learning curve in a new MRI-based cervical brachytherapy program.

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 (D_2cc) to organs at risk were used to assess dosimetry. Statistics were performed with t tests and Kaplan-Meier method.

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 D_2cc 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). D_2cc rectum decreased from 69.3 Gy to 62.6 Gy (p = 0.01), and D_2cc bladder trended lower from 87.5 Gy to 83.6 Gy (p = 0.09).

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.