The use of transrectal ultrasound to improve gynecologic interstitial applicator implantation

Brachytherapy is essential for treating locally advanced cervical cancer and vaginal recurrences post-hysterectomy. While MRI and CT have permitted volumetric planning, precise interstitial applicator placement remains crucial for optimal dosimetry. We evaluated the impact of transrectal ultrasound (TRUS) on interstitial gynecologic brachytherapy needle utilization and dosimetry.

A retrospective single institute study was conducted of patients requiring interstitial brachytherapy between 2020 and 2023. Cases were categorized based on TRUS use. Endpoints included number of needles placed, removed, unloaded channels, and dosimetry to the high risk clinical target volume (CTV_HR) and organs at risk.

A total of 142 implants were performed on 139 patients; 58 % did not utilize a tandem, representing post-hysterectomy recurrences or primary vaginal cancers. Mean CTV_HR volume was 59 cc. TRUS was used in 73 % of cases and was associated with 4-5 fewer needles per implant, independent of CTV_HR volume. With TRUS, needle removal at simulation decreased from 41 % to 3 % (p < 0.001), and plans with unloaded needle channels decreased from 76 % to 25 % (p < 0.001). Despite fewer needles, CTV_HR coverage among definitive cervical cancers remained comparable (D90 > 85 Gy EQD2 in 79 % with TRUS and 78 % without). The ABS rectal constraint of D2cc < 75 Gy was met more often with TRUS (92 % vs. 56 %, p < 0.001).

TRUS improves interstitial needle placement efficiency and rectal dosimetry without compromising target coverage. Its accessibility supports broader integration into gynecologic brachytherapy workflows as a practical optimization tool for achieving disease control and minimizing toxicity.