Kana Takahashi

Technical report on the first clinical use of a bioabsorbable PGA spacer in HDR brachytherapy for recurrent cervical cancer

Abstract In recurrent gynecologic malignancies following prior pelvic irradiation, definitive radiation therapy is often precluded by cumulative dose constraints to adjacent organs at risk (OARs), and patients may be left with only highly invasive surgical options such as total pelvic exenteration. While some institutions have explored displacement techniques such as artificial ascites or hyaluronic acid gel injection, these approaches are not widely adopted and frequently fail to ensure consistent and stable separation of OARs. We report the first clinical use of Neskeep®, a bioabsorbable polyglycolic acid (PGA) spacer, in high-dose-rate (HDR) brachytherapy for recurrent cervical cancer after prior pelvic radiation. A woman in her 40s with prior hysterectomy and HDR brachytherapy for cervical intraepithelial neoplasia grade III developed vaginal stump recurrence 4 years later. Laparoscopic placement of the PGA spacer was performed to achieve durable displacement of the small bowel, followed by eight fractions of HDR brachytherapy. Hyaluronic acid gel was also injected during each fraction to displace the bladder and rectum. The spacer maintained position and volume throughout treatment without complications. Dose–volume analysis showed a marked reduction in small bowel D₂cc (mean equivalent dose in 2 Gy fractions (EQD₂): 121.6 cGy) compared to the initial treatment (606.0 cGy), while the spacer itself received a mean D₂cc of 690.3 cGy. MRI confirmed complete response at 2 months, with no adverse events observed at that time point. The PGA spacer enabled safe, curative reirradiation in a case that would otherwise be unsuitable for further radiation therapy.

Gel spacer-assisted salvage brachytherapy for pelvic recurrence after definitive chemoradiotherapy in cervical cancer: A single-institution retrospective study

To evaluate the safety and efficacy of gel spacer-assisted high-dose-rate (HDR) salvage brachytherapy for pelvic recurrence after definitive chemoradiotherapy (CRT) for cervical cancer. We retrospectively analyzed 15 consecutive patients who underwent salvage HDR interstitial brachytherapy for pelvic recurrence following definitive CRT for cervical cancer between 2016 and 2024. Gel spacers were injected between the recurrent tumors and adjacent organs at risk (OARs), mainly the rectum and bladder, under transrectal ultrasound guidance at each brachytherapy session. The spacer's effectiveness was evaluated by comparing the hypothetical dose delivered to the gel spacer volume (assuming no spacer was used) with the actual dose to the OARs. The median biological equivalent dose in 2-Gy fractions (EQD2, α/β = 10) delivered during reirradiation was 64.0 Gy (range: 44.5-72.0 Gy). After a median follow-up of 22 months (range: 0-93 months), the complete response rate was 66.7% (10/15). Gel spacer injection significantly reduced the rectal D2cc by a median of 29% (interquartile range [IQR]: 14%-55%) and the bladder D2cc by 16% (IQR: 10%-34%) compared with the hypothetical dose estimates assuming no spacer use (Wilcoxon signed-rank test, p < 0.001). Grade ≥3 late toxicities occurred in only one patient (10.0%) among complete responders, and no spacer-related adverse events were observed. Gel spacer-assisted salvage brachytherapy significantly reduced radiation exposure to critical OARs, particularly the rectum, while achieving effective tumor control in patients with pelvic recurrence of cervical cancer after definitive CRT. These promising results support this approach as a feasible and safe strategy, warranting further validation in larger prospective studies.

Evaluation of the dosimetric impact and safety of MucoUp as a spacer in gynecologic brachytherapy

Gynecologic brachytherapy (BT) is an essential component of definitive radiation therapy, but excessive radiation exposure to organs at risk (OARs) remains a major concern. MucoUp, a hyaluronic acid-based spacer, has been introduced to physically separate the high-risk clinical target volume (HR-CTV) from adjacent OARs. However, its clinical feasibility and dosimetric impact remain underexplored. This study aimed to evaluate the dosimetric impact and clinical feasibility of MucoUp in high-dose-rate (HDR) gynecologic BT. A retrospective analysis was conducted on 5 patients with gynecologic malignancies who underwent HDR BT with and without MucoUp injection. Dosimetric parameters, including HR-CTV D90 and OAR D2cc (bladder, rectum), were compared between sessions with and without MucoUp. Spacer volume retention was assessed using pre- and post-treatment CT scans. MucoUp injection resulted in a significant reduction in rectal D2cc (7.19 Gy vs. 6.73 Gy, p = 0.043), while maintaining HR-CTV dose coverage (D90: 8.82 Gy vs. 9.15 Gy, p = 0.043). A nonsignificant reduction in bladder D2cc was observed (7.51 Gy vs. 7.16 Gy, p = 0.34). Spacer volume retention remained stable throughout treatment. No procedural complications or acute toxicity were observed. This study suggests that MucoUp is a promising spacer for gynecologic BT, effectively reducing rectal dose while preserving HR-CTV coverage. Given its high stability and safety, MucoUp may serve as an alternative to existing spacer materials. Further large-scale and long-term studies are warranted to evaluate its impact on late toxicities.