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Outpatient Interstitial Implants–Integrating Cesium-131 Permanent Interstitial Brachytherapy into Definitive Treatment for Gynecologic Malignancies

      Purpose

      Curative intent brachytherapy for gynecologic cancers most often involves intracavitary approaches. In the less common clinical scenarios that require interstitial brachytherapy, template-guided after-loading techniques (e.g. Syed-Neblett interstitial implants) are generally used, yet patients might not be offered this option due to perceived risks or limitations in facilities, equipment, and expertise. Permanent Interstitial Brachytherapy (PIB) with Cs-131 in the outpatient setting is a relatively new procedure that expands brachytherapy options for women who might benefit from interstitial treatment. Our experience suggests that this option is exceptionally effective and safe in the curative management of selected gynecologic cancers for whom interstitial radiation techniques are indicated.

      Materials and Methods

      Between August 2012 and November 2015, 22 patients received a total of 25 Cesium-131 PIB procedures at our institution as a component of definitive therapy for gynecologic malignancy following pelvic radiation therapy (PRT) with/without intracavitary brachytherapy (ICB). Paterson-Parker rules were used to calculate activity and seed distribution. Cumulative doses were calculated using Biological Effective Dose (BED) and Equivalent Dose at 2 Gy per fraction (EQD2) formalism.

      Results

      Median follow up was 16 months (range 1.3-39.4). Primary diagnoses included Uterus (n=12), Cervix (n=2), and Vaginal (n=10). Cell types included squamous cell (n=7), endometrioid adenocarcinoma (n=7), melanoma (n=3), serous (n=2), adenosquamous (n=1), clear cell (n=1), and small cell (n=1). Histologic grades included grade 1 (n=4), grade 2 (n=8) and grade 3 (n=10). Indications for interstitial brachytherapy were gross residual disease with thickness 0.5-1.5 cm (n=12), positive surgical margin (n=4), and inability to undergo a Syed-Neblett template implant due to medical co-morbidities (n=6). The median external beam dose to the pelvis was 45 Gy (37.5 Gy–50.4 Gy) and eleven patients received ICB consisting of 1 or 2 insertions of 7 Gy each. The median Cs-131 dose for PIB was 25 Gy to permanent decay, prescribed at 5 mm depth (16-50 Gy). The median cumulative BED was 90.8 Gy and median EQD2 was 75.7 Gy. All patients remain locally controlled, and no grade 3 toxicities have occurred. All PIB procedures were conducted on an outpatient basis. Only 2 patients required sedation beyond local injection of Lidocaine with Epinephrine combined with oral anxiolytics. No patient required hospitalization following PIB.

      Conclusions

      Permanent interstitial brachytherapy using Cesium-131 is a highly safe and effective treatment modality for primary management of small volume gross disease in gynecologic malignancies. Furthermore, PIB allows the benefits of interstitial therapy to be expanded to patients who might not otherwise be candidates due to medical co-morbidities or other factors.