2905 - Initial Experience Utilizing Universal Interstitial Cylinder in Gynecologic Cancers
Presenter(s)
R. Zitter1, T. Wu2, M. J. Gutman3, J. J. Sohn4, D. K. Dietrich5, Z. Tian6, C. H. Son4, and Y. Hasan4; 1University of Chicago, Chicago, IL, 2Department of Radiation and Cellular Oncology, The University of Chicago Medicine, Chicago, IL, 3Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL, 4Department of Radiation and Cellular Oncology, University of Chicago Medical Center, Chicago, IL, 5University of Chicago Pritzker School of Medicine, Chicago, IL, 6Department of Radiation & Cellular Oncology, The University of Chicago, Chicago, IL
Purpose/Objective(s): We report one of the first high dose rate (HDR) brachytherapy clinical and dosimetric experience with follow up using the Universal Interstitial Cylinder (UIC) as a more utilitarian hybrid applicator in lieu of a template interstitial approach.
Materials/Methods: Women who underwent HDR brachytherapy with UIC at two large academic centers were reviewed. With IRB approval, patient data was retrospectively evaluated for clinical response, toxicity, and dosimetric parameters.
UIC’s were preassembled with needles and advanced interstitially under ultrasound guidance when appropriate without template. Source dwell times were optimized as needed for normal organs. Needle positions at depths up to 4.5 cm cephalic to the os/cuff were recorded for 30 mm and 35 mm diameter cylinders. Needle deviation was assessed by measuring the cephalic extension of the target =2 cm lateral from the central tandem and compared to the positions of implanted needle tips.Results: From 2022 to 2025, outcomes of 30 women underwent HDR brachytherapy with UIC were reviewed. The cohort consisted of African American (14), White (12), Asian (3) and Hispanic (1) patients. Diagnoses included cervical (53%), vaginal (17%), endometrial (23%), and other cancers (7%). Staging at time of RT was stage I (7), II (1),III (11), IV (2), or recurrent (9). The majority received UIC during their primary treatment course (73%). Treatment included external beam radiation (EBRT) in 27 of whom 21 received concurrent chemotherapy (cisplatin n=19 and pembrolizumab n=4). With median follow up of 10.4 months (range 0.1-28.1), 90% had complete clinical response, and 87% had complete local radiographic response. While undergoing EBRT, toxicities were limited (N=2 Grade 2+ GI, N=2 GU Grade 2+, no skin toxicity). While using UIC HDR treatment, additional Grade 2+ GU and GI toxicities were experienced by 2 patients. Late toxicities (new since HDR and present at first follow up at a min of 3 months) were 17% of patients experiencing GU Grade 2+, 10% GU Grade 1, and 20% GI Grade 1. Interstitial needles were placed in 18 patients. Both 30 and 35mm UIC resulted in needle placement 1.8-3.8 cm (mean+/-std: 2.5+/-0.4) lateral from the tandem while the 35mm UIC showed favorable needle placement for wider targets closer to the os. Larger uncertainties were observed as needles reached further cephalad. For patients with target extension =2cm lateral from the tandem, 11 had needle placement via UIC that reached cephalic to the target, while 5 patients required freehand needle placement to optimize coverage. The total EqD2 for patients receiving EBRT+ UIC to the target ranged from 67.4-91.1 Gy.
Conclusion: The UIC allows HDR brachytherapy for patients with wider or eccentric target volumes, with favorable control and toxicity at early follow-up. While optimization with free-hand needles may still be needed in select cases, the adaptability of this applicator may provide a more accessible option for practitioners.