3571 - Interstitial High-Dose Rate Brachytherapy with or without Interstitial Hyperthermia for Gynecologic Malignancies

A. D. Thompson¹, A. E. Pollock², B. Savla³, P. Mohindra⁴, R. F. Krc¹, J. D. Cohen⁵, K. Sun⁶, D. Rodrigues⁷, M. Guerrero³, N. Lamichhane¹, S. A. McAvoy³, J. K. Molitoris³, Z. H. Rana⁸, D. Kunaprayoon³, K. Marter¹, D. M. Roque⁹, G. Rao⁹, S. M. Bentzen³, and E. M. Nichols⁷; ¹Department of Radiation Oncology, University of Maryland Medical Center, Baltimore, MD, ²Inspire Oncology, Naples, FL, ³Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, ⁴University Hospitals Seidman Cancer Center, Cleveland, OH, ⁵WellSpan Medical Group, York, PA, ⁶Division of Biostatistics and Bioinformatics, University of Maryland Greenebaum Cancer Center, and Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, ⁷University of Maryland School of Medicine, Baltimore, MD, ⁸Maryland Proton Treatment Center, Baltimore, MD, ⁹Division of Gynecology-Oncology, University of Maryland School of Medicine, Baltimore, MD

Purpose/Objective(s): Multi-catheter interstitial high-dose rate brachytherapy (IHDR) with interstitial hyperthermia (IHT) has been shown to improve oncologic outcomes with minimal added toxicity for newly diagnosed cervical cancer. However, similar data for other gynecologic (GYN) cancers is limited, and it is not clear which patients may benefit most from the addition of IHT. We present a single-institution experience of patients with GYN cancers treated using IHDR with or without concurrent IHT (IHDR-IHT). Materials/

Methods: We retrospectively analyzed 97 patients with GYN cancers treated with IHDR with or without IHT (IHDR: 36, IHDR-IHT: 61) from 2015-2023. Primary indications for IHT included more advanced or treatment resistant disease such as recurrent, residual (following EBRT), or bulky tumor, guided by tumor location and geometry of needle placements within the HRCTV. IHDR was delivered 5 times over a 3-day period with a total of 2 IHT treatments (target temperature 40-44 °C for 1 hour) between IHDR treatments using the same set of catheters. Oncologic and toxicity outcomes were compared for both arms.
Results: Median follow up was 19.4 months for IHDR-IHT and 17.7 months for IHDR. Chi-square analysis showed that IHDR-IHT was more likely to have 3+ high risk characteristics which included minority race, non-cervical GYN histology, stage III+, re-irradiation, or recurrent disease (IHDR-IHT: 16.4%, IHDR: 2.8%, p=0.041). Addition of IHT was well tolerated with similar rates of grade 2 or higher late toxicity compared to IHDR alone (IHDR-IHT: 14.75%, IHDR: 25%, p=0.155). On univariate analysis, IHDR-IHT had worse local failure free survival (IHDR-IHT: 75.4%, IHDR: 91.7%, p=0.047), defined as the time interval between last day of IHDR treatment to date of local recurrence. Cox regression showed that non-cervical GYN histology (HR 9.5 [95% CI 1.2-78.3] p=0.036), recurrent disease (HR 6.6 [95% CI 1.3-33.1] p=0.023), re-irradiation (HR 9.8 [95% CI 1.9-50.3] p=0.006), and minority race (HR 4.3 [95% CI 0.98-18.9] p=0.055) were associated with higher cumulative incidence rates for local failure in the IHDR-IHT group. These risk factors did not predict local failure for IHDR alone.
Conclusion: In this retrospective analysis we were unable to demonstrate an improvement of local failure free survival with the addition of IHT to IHDR. These worse outcomes observed for the IHDR-IHT group are likely due to worse prognostic factors of minority race, non-cervical GYN histology, higher staging, re-irradiation, or recurrent disease. Despite this, long term local control was observed in an otherwise unfavorable patient population, and the addition of IHT showed a similar toxicity profile. Future prospective studies involving a more homogenous GYN cancer population are warranted to clarify which patients benefit most from the addition of IHT to IHDR.