Single application hybrid interstitial brachytherapy for cervical cancer: An institutional approach during the COVID-19 pandemic

Introduction
To ease anesthesia and inpatient strain during the COVID-19 pandemic, our institution’s policy for hybrid intracavitary-interstitial brachytherapy (IC/ISBT) for cervical cancer (CC) was modified from multiple applications (MA) treated over 2 separate weeks (7 Gy × 4) to a single-application (SA), treated within 1 week (8 Gy × 3). Here, we assessed dosimetric quality of the SA hybrid IC/ISBT approach and report our early outcomes.

Material and methods
This was an IRB-approved retrospective review of CC patients treated with magnetic resonance imaging (MRI)-guided hybrid IC/ISBT between April 1, 2020 and December 31, 2020 (COVID cohort). Treatment parameters and quality indicators were compared to hybrid IC/ISBT cases treated in 2 years prior (pre-COVID cohort). Differences between cohorts were evaluated with the Mann-Whitney U-test.

Results
In the COVID compared to pre-COVID cohort, median high-risk clinical target volume (HR-CTV) was similar: 33.3 vs. 33.9 cc, as was cumulative HR-CTV D90%: 81.2 vs. 80.9 Gy. Organ-at-risk D2cc values and recto-vaginal point doses were similar. Median number of channels loaded was increased to 6 vs. 4 (p = 0.002), but percentage of total dwell time allocated to needles remained similar: 13% vs. 15%. Median implant HR-CTV D90% was higher: 107.8% vs. 98.4% (p = 0.001), and there was a trend toward reduced overall treatment time (OTT): 44 days vs. 53 days (p = 0.1). Local control was achieved in all patients, but mucosal toxicity was higher in the COVID group, with grade 2 or higher vaginal, genitourinary, or gastrointestinal events recorded in 56% of the patients.

Conclusions
The SA hybrid IC/ISBT approach utilized during the COVID-19 pandemic maintained similar plan characteristics as pre-pandemic MA hybrid cases, while simultaneously reducing anesthesia, inpatient resources, and OTT. Local control outcomes demonstrate the regimen was effective; however, given the increased risk of mucosal toxicity, we conclude that the SA regimen should be considered only when a MA schedule is not feasible.