Replacing the Syed: Initial Safety Results of a New Interstitial Template Technique using Cesium-131 Permanent Interstitial Brachytherapy (PIB) for Advanced Gynecologic Cancers

Interstitial brachytherapy is an essential component of treatment for selected gynecologic cancers, yet practice patterns suggest significant underutilization. Currently used low and high dose rate template-guided techniques require prolonged bedrest, with attendant short and long term risks. We present a novel technique utilizing Permanent Interstitial Brachytherapy (PIB) performed as an outpatient procedure with minimal toxicity and favorable early outcomes. The first 22 patients treated at our institution using a template-guided PIB implant with minimum 6 months follow-up were reviewed. Cases were pre-planned using Eclipse Brachy Planning on a dedicated CT study set, and performed under conscious sedation using a modified Syed-Neblett template that enabled ultrasound guidance. Cesium-131 sources with were placed for treatment of the bladder base (n=4), pelvic side wall (n=9), vaginal apex (n=3), vulva/perineal body (n=2), and a peri-rectal recurrence (n=2). All patients were discharged the same day of the procedure. Patients underwent CT scanning and post-planning both immediately post procedure and again 2-3 weeks post implant. Patients were followed monthly and assessed using Radiation Therapy Oncology Group (RTOG) toxicity criteria. Median age was 68 years (35-86). Primary sites included cervical cancer (n=5), vaginal cancer (n=6), vulvar cancer (5)., An additional 6 patients were re-irradiated for recurrence of uterine (n=5) and ovarian cancers (n=1). Histologies included squamous (n=16), adenocarcinoma (n=4), serous (n=1), and carcinosarcoma (n=1); greater than 70% were grade 3. The median prescription dose was 25 Gy (range 15 – 55 Gy) to a median volume of 22.4 cm3 (range 4.8 – 122.9 cm3). A median of 9 needles were used (range 4-21), with median active length of 5 cm (range 3-10 cm), and median source strength of 1.22 u/seed (0.75 – 2.01 u/seed). The median V100 was 96.73% (range 84.3-100%). Toxicities attributable to PIB were minimal. One patient with an advanced vaginal tumor involving the rectovaginal septum developed grade 2 acute and late diarrhea attributed to the implant. Two patients definitively re-irradiated to >100 Gy cumulative to the lower 1/3 of the vagina developed grade 1 and a grade 3 soft tissue necroses, respectively. The first patient remained without symptoms, while the second required suprapubic catheter placement for severe dysuria. After a median follow-up of 7.5 month, 5 patients (22.3%) had manifest a local recurrence – 3 isolated, and 2 in combination with either regional or distant progression. Outpatient template-guided interstitial brachytherapy using this novel PIB technique can be completed safely and with at least equivalent outcomes to traditional interstitial brachytherapy techniques. Additional follow-up and cases will clarify long term risks and outcomes.