Effective Timing of Hyaluronate Gel Injection in Image-Guided Adaptive Brachytherapy for Uterine Cervical Cancer: A Proposal of the “Adjusted Dose Score”

Abstract

Abstract Background Hyaluronate gel injection (HGI) in the rectovaginal septum (RVS) and vesicovaginal septum (VVS) is an effective method in the setting of high-dose-rate image-guided adaptive brachytherapy (IGABT) for cervical cancer. We retrospectively investigated the optimal conditions for HGI to achieve optimal dose distribution with a minimum number of HGI. Methods Fifty IGABT plans of 13 patients with cervical cancer who received IGABT both with and without HGI in the RVS and VVS were classified into the following two groups: the plan with (numbers of plans = 32) and the plan without (numbers of plans = 18) HGI groups. The irradiation dose parameters of high-risk clinical target volume (CTVHR) and organs at risk (OARs) per fraction were compared between the two groups. We also developed the adjusted dose score (ADS), reflecting the overall irradiation dose status for four OARs and CTVHR in one IGABT plan, and investigated its utility. Results HGI reduced the maximum dose to the most exposed 2.0 cm3 (D2.0 cm3) of the bladder while increasing the minimum dose covering 90% of CTVHR and the percentage of CTVHR receiving 100% of the prescription dose in one IGABT plan without causing any associated complications. The ADS of ≥ 2.60 was the optimum cut-off value to decide whether to perform HGI. Conclusions HGI is a useful procedure for improving target dose distribution while reducing D2.0 cm3 in the bladder in a single IGABT plan, and the ADS can be useful in determining the implementation of HGI.