Safe dose escalation and reduction of the fraction number of uterine cervical brachytherapy using a gel spacer in the rectovaginal and vesicouterine septum: A planning study.

Purpose: To evaluate the possibility of dose escalation and reduction of fraction number in cervical brachytherapy using a gel spacer.

Material And Methods: Twenty patients with uterine cervical cancer treated with image-guided adaptive brachytherapy (IGABT) were selected. Hyaluronic acid gel injection (HGI) was performed in the rectovaginal and vesicouterine septum for 10 patients. The other ten patients were not with HGI. Both groups were treated with IGABT involving tandem/ovoid or cylindrical applicators along with additional interstitial needles. Dose distributions approved by radiation oncologists were retrospectively analyzed, and a dose summation of 45 Gy/25 of external beam radiation therapy and IGABT was performed. Dose constraints for D of bladder, rectum, and sigmoid were 80, 70, and 70 Gy, respectively. Equivalent dose in 2-Gy fractions calculations used α/β = 10 Gy for high-risk clinical target volume (CTV) D and α/β = 3 Gy for organs at risks (OARs). As a planning study, dose distribution rescaling was conducted to deliver as much dose to CTV D as possible within the dose constraint limitation for OARs when IGABT was performed for four, three, and two fractions in both groups.

Results: The median CTV D was >80 Gy in the non-HGI group and >85 Gy in the HGI group for virtual two and three fractions. Rectum D was significantly lower in the HGI group for three fractions (p < 0.01).

Conclusions: In the HGI group, adequate dose delivery to CTV could be achieved with a reduced IGABT fraction number while meeting the dose constraints of OARs.