High-dose-rate interstitial brachytherapy for gynecologic malignancies

The study aimed to assess the outcome of locally advanced cervical and vaginal cancer treated with high-dose-rate interstitial brachytherapy (HDRB).

Between 1998 and 2004, 16 previously unirradiated patients with locally advanced cervical and vaginal cancer not suitable for intracavitary brachytherapy because of distorted anatomy or extensive vaginal disease were treated with HDRB in combination with external beam radiotherapy. All patients received whole pelvis external beam radiation therapy (EBRT) followed by interstitial implantation. The median whole pelvis external beam dose was 45 Gy (range, 39.6-50.4 Gy) with 11 patients receiving parametrial boost to a median dose of 9 Gy. Twelve (75%) of these patients received chemotherapy concurrent with external beam. All patients received a single HDRB procedure using a modified Syed-Neblett template. A CT scan was performed postimplant for needle placement verification and treatment planning purpose. Dose was prescribed to the tumor volume based on the radiographic and clinical examination. All patients received 18.75 Gy in five fractions delivered twice daily. The median followup was 25 months (6-69 months).

Median cumulative biologic effective dose (EBRT+HDRB) to tumor volume was 78.9 Gy10 with the range of 72.5-85.2Gy10. Median cumulative biologic effective dose for the rectum and bladder were 99.4 Gy3 (range, 79.6-107.8 Gy3) and 96.4 Gy3 (range, 78.3-105.3 Gy3), respectively. Complete response was achieved in 13 (81%) patients with 3 patients having persistent disease. Five of these 13 patients developed recurrence at a median time of 14 months (distant in 4 and local and distant in 1). The 5-year actuarial local control and cause-specific survival were 75% and 64%, respectively. In subset analysis, 5-year actuarial local control was 63% for cervical cancer patients and 100% for vaginal cancer patients. No patient had acute Grade 3 or 4 morbidity. Grade 3 or 4 delayed morbidity resulting from treatment occurred in 1 patient with 5-year actuarial rate of 7%. Three patients had late Grade 2 rectal morbidity and 1 patient had Grade 2 small bowel morbidity.

Our series suggests that single interstitial implantation procedure with five fractions of 3.75 Gy each to target volume is an effective and safe fractionation schedule. The integration of imaging modality helps in decreasing dose to the critical organs. Additional patients and followup are ongoing to determine the long-term efficacy of this approach.