S. Patel, S. Jani, D. Pinnaduwage, D. Kramer, S. T. Ellefson, S. P. Sorensen, A. Z. Diaz, N. Thawani, and S. P. Srivastava; Dignity Health Cancer Institute, Phoenix, AZ
Purpose/Objective(s):In our practice, transrectal ultrasound (TRUS)-guided template interstitial HDR brachytherapy is utilized as a boost to treat patients with locally advanced cervical cancer with disease not amenable to hybrid interstitial therapy. Three separate implants are performed for each patient. During each implant, the physician decides on the number of catheters based on real-time TRUS assessment of cervical disease. Thus the same patient could require a different number of catheters during each implant based on their disease and organ anatomy. Over time, one question arose: would more catheters help even beyond the real-time TRUS assessment? The aim of this study was to assess this question by analyzing coverage and organ dosimetry with respect to the number of catheters implanted. Materials/
Methods: From January 2022 to December 2023, all patients with locally advanced cervical cancer (FIGO stage II-IV) who underwent pelvic with or without paraaortic nodal radiation followed by TRUS-guided interstitial HDR were included in this retrospective analysis. The number of catheters (NoC), ctv volume, V95%, V90%, D90%, rectal D2cc, sigmoid D2cc, and bladder D2cc were recorded. CTCAE toxicity, local (cervical) control, distant control, and survival data were noted. A partial correlation was utilized to assess the relationship between NoC and ctv volume, as greater disease volume may confound the NoC. Subsequently multiple regression analyses were performed to evaluate the impact of NoC on coverage and organ dosimetry. Results: Twenty-one consecutive patients underwent 63 implants and received 8 Gy per implant. The median NoC used per implant was 10 (range 9-15). The median ctv volume was 94 cc (24-261). The mean V95%, V90%, and D90% were 93.5%, 96.2%, and 101%, respectively. The mean rectal D2cc, sigmoid D2cc, and bladder D2cc were 4.4 Gy, 4.7 Gy, and 5.9 Gy, respectively. There were no reported CTCAE grade >2 toxicities. At a median follow-up of 6 months (0-20), local control, distant control, and overall survival were 100%, 68%, and 95%. There was a significant partial correlation between NoC and ctv volume (Pearson’s r 0.475, p<0.001). Multiple regression analyses revealed a greater NoC to predict for higher V95% (ß 0.28, p=0.049) and higher D90 (ß 0.33, p=.018) but not improved organ dosimetry. Conclusion: While the addition of even more interstitial catheters at time of TRUS-based cervical cancer implantation did improve dosimetric coverage, it did not appear to improve organ dosimetry. As there were no local failures at short term follow-up, it is unclear whether the small improvement in coverage is clinically worth the additional tissue trauma and increased risk for acute bleeding. Longer-term follow-up is warranted, and additional studies may help.