R. S. Davis1, R. Mulherkar2, Z. Iqbal3, C. J. Ladbury1, Y. J. Chen1, H. Kim4, S. Beriwal5, K. V. Albuquerque6, J. A. A. Vargo IV7, and S. M. Glaser1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2Drexel University College of Medicine, Philadelphia, PA, 3Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 4Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 5Allegheny Health Network Cancer Institute, Department of Radiation Oncology, Pittsburgh, PA, 6Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 7UPMC Cancer Center, Pittsburgh, PA
Purpose/Objective(s): Despite advances in intracavitary or hybrid brachytherapy (BT), patients with more extensive or recurrent gynecological cancer require treatment with a more comprehensive interstitial (IS) implant. This population is understudied due to poor outcomes and complex, resource intensive treatments that limit widespread adoption. Materials/
Methods: We performed a retrospective, multi-institutional analysis of patients with gynecologic cancer treated with template-based transperineal ISBT. This report comprises data from 3 high-volume centers in the United States with expertise in intracavitary/hybrid brachytherapy and thus such interventions were deemed insufficient for the included patients. All patients were treated with a minimum of CT-based 3D brachytherapy. Results: Between 2006 and 2022, 319 patients underwent ISBT. Median age at diagnosis was 61 (IQR 53-70). Racial/ethnic background was 37% Hispanic white, 36% non-Hispanic white, 13% black, and 13% Asian. At time of BT, primary tumor site was cervix (53%), vaginal cuff (19%), vagina (19%), uterus (7%), vulva (1%), and urethra (1%). Patients were treated for recurrent disease in 21% of cases. Histologies included squamous cell carcinoma (63%), Adenocarcinoma (28%), melanoma (1%), and other (8%). Median tumor size was 5.7 cm (IQR 4-7.1). Lymph node positivity rate was 63%. Nearly all patients (98%) received EBRT and 93% received IMRT to a median dose of 45 Gy (94% received 45-50.4 Gy). Concurrent chemotherapy was delivered to 88% of patients. A median of 19 needles (IQR 16-23) were used per implant and 99% of patients were treated with a single implant. Median HRCTV volume was 57 cc (IQR 33.25-89.38). Median D90 to HRCTV was 78 Gy (IQR 75.5-80.3). Median D2cc, in Gy, to bladder, rectum, sigmoid, and bowel were, 68.4 (IQR 61.2-74.6), 62.2 (IQR 57.8-65.4), 55.4 (IQR 50.6-61.7), 52.8 (IQR 49-58.1) respectively. Median follow-up was 22.5 (IQR=9.8-56.2) months and 31.4 (15.1-72.3) months for living patients. Overall survival at 3 and 5 years were 50.2% (95% CI 44-56.4%) and 43.1% (95% CI 36.5-49.7). Freedom from local, regional, and distant recurrence at 5 years was 75.3% (95% CI 68.9-81.7), 78.5% (95% CI 70.9-85.1), and 56.1% (95% CI 49.1-63.1). Grade =3 toxicity was experienced by 11% of patients, primarily fistula formation. Primary tumor site and de novo vs recurrent cancer were strong predictors of overall survival with an OS at 3 years of 45.3% (95% CI 36.5-54.1) for cervical cancer and 70.2% (95% CI 57.6-82.8) for vaginal cuff recurrences (log-rank p<0.01) Additional subset analysis and MVA of factors predictive for survival and toxicity will be presented. Conclusion: In this, the largest series of its kind, we demonstrate that template-based ISBT is an effective treatment for patients with extensive gynecologic cancer not amenable to an intracavitary or hybrid approach. Physicians and patients should be aware of the risk of fistula formation. Distant metastasis remains the primary mode of failure.
