Abstract
We use transrectal ultrasound (TRUS)-guided template interstitial HDR brachytherapy as a boost to treat patients with advanced cervical cancer not amenable to hybrid interstitial therapy. Three separate implants are performed for each patient with the physician deciding on the number of catheters based on real-time TRUS assessment of cervical disease. Consequently, the same patient could require a different number of catheters during each implant based on their disease and organ anatomy. We provide an update on whether increasing the number of catheters during implantation led to improved coverage and organ dosimetry.
From January 2022 to June 2024, 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 are included in this 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.
Twenty-nine consecutive patients underwent 87 implants and received 8 Gy per implant. The median NoC used per implant was 10 (range 7-18). The median ctv volume was 93 cc (15-401). The mean V95%, V90%, and D90% were 94%, 96%, and 102%, respectively. The mean rectal D2cc, sigmoid D2cc, and bladder D2cc were 4.3 Gy, 4.6 Gy, and 5.9 Gy, respectively. There were no reported CTCAE grade >2 toxicities. At a median follow-up of 10 months (0-31), local control, distant control, and overall survival were 100%, 68%, and 89%. There was a significant partial correlation between NoC and ctv volume (Pearson’s r 0.672, p<0.001). Multiple regression analyses revealed a greater NoC to predict for higher D90 (β 0.31, p=0.029) as well as V95 and V90 but the latter two did not reach significance (p=0.07). A greater NoC did not improve organ dosimetry.
While the addition of even more interstitial catheters at time of TRUS-based cervical cancer implantation did improve dosimetric coverage, it continues to not meaningfully impact organ dosimetry. As there were still no local failures at 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 with additional patients may help clarify this further.