Impact of hyaluronic acid (HA) rectal spacer quality score (SQS) and fischer-valuck (FV) spacer symmetry score on rectal dosimetry and acute and late gastrointestinal (GI) toxicity outcomes - an Australian experience.

Abstract

Purpose/Objective(s): To assess implant quality using modified SQS (mSQS) and FV scores achieved in 100 men with localized prostate cancer (PCa) treated with moderately hypofractionated external beam radiotherapy (EBRT) who underwent stabilized HA rectal spacer (RS) implant, and its impact on acute and late GI toxicity. Materials/Methods: This retrospective multi-institutional review involved 100 consecutive men with localized PCa treated with moderately hypofractionated EBRT (60Gy/62Gy in 20#) and underwent HA RS insertion, treated between June 2020 - September 2022. Statistical metrics were used to assess patient and disease characteristics. Acute and late GI toxicity were assessed using CTCAEv5. Implant quality was assessed using mSQS (recto-prostatic separation (RPS)), FV score (symmetry) and RS rectal wall infiltration (RWI) evaluated on post implant T2-weighted MRI axial slices. RWI was independently assessed by an MRI prostate specialist radiologist. SQS, RWI and FV scoring were performed according to prior publications by Grossman et al and Fischer-Valuck et al. mSQS scores were used to stringently account for our PTV expansions (mSQS score 2 = >=10mm RPS, mSQS score 1 = 6-9mm RPS, mSQS score 0 = <=5mm RPS). Result(s): The mean age was 74.6 years (SD 6.0 y); 54 patients had unfavorable intermediate risk PCa, 33 had favorable intermediate risk PCa and 9 had low risk PCa. 88 patients were treated to 60Gy/20#, while 12 patients were treated to 62Gy/20#. Of the RS implants, 98% were deemed "very easy" by the injector and 2% were deemed "easy". Overall mSQS score of 1 ("good") was achieved in 74 patients, score of 2 ("excellent") in 24 patients, and a score of 0 occurred in just 2 patients. 97% of the injectors successfully shaped HA to achieve symmetrical rectal spacing with FV score 1. Median rectal V36 was 13.2% (IQR 9.2-17.5), V42 was 8.4% (IQR 5.4-12.3), V48 was 5.1% (IQR 2.7-8.2), V54 was 2.1% (IQR 0.9-4.5) and V57 was 0.9% (IQR 0.2-2.3). Seven acute G1 and 5 late G1 GI toxicities were recorded. There was no >=G2 acute or late GI toxicity. No statistically significant association was identified between FV and SQS scores with acute or late GI toxicity incidence. Only 1 patient experienced implant RWI and the RWI was reversed with hyaluronidase, with no significant sequelae reported. He was subsequently reimplanted successfully with HA RS and completed EBRT uneventfully. Median follow-up was 1.68 years (IQR: 1.28-2.23), with only one regional recurrence reported. Conclusion(s): The majority (97%) of patients who underwent HA RS implant had easily achieved high quality RS (both modified SQS scores 1-2 and FV score 1). This translated to low rectal doses and low incidence of acute and late G1 GI toxicities. Stabilized HA RS may be considered in patients undergoing hypofractionated EBRT to the prostate.Copyright © 2024