Prospective Observational Trial of an Absorbable Hydrogel Spacer in Prostate Cancer Radiotherapy: Quality of Life and Dosimetric Outcomes

Abstract

A hydrogel spacer is an FDA approved medical device designed to increase the distance between the rectum and the prostate during radiotherapy to minimize morbidity. Its use provides favorable dosimetry for conventional radiotherapy and has become a standard at our institution. We therefore sought to prospectively observe the quality of life (QOL) outcomes and dosimetric profiles for patients receiving hydrogel spacers. We prospectively enrolled 30 patients between 10/2016 and 10/2018. Inclusion criteria required low risk or favorable-intermediate risk patients as defined by clinical stage T1-T2, Gleason ≤ 3+3 or select 3+4 with low volume disease. Patients completed baseline Expanded Prostate Cancer Index Composite (EPIC-26) and American Urological Association symptom index (AUA-SI) questionnaires. A hydrogel spacer was placed for all patients who then received stereotactic body radiation therapy, low dose rate brachytherapy, conventionally fractionated radiation therapy, or moderately hypofractionated radiation therapy. We evaluated post-implant dosimetry to critical structures, and prospectively collected follow-up surveys. For inferential statistics we performed a repeated measures analysis of variance to compare patient specific response and correlated survey data with dosimetric metrics by generating linear regression models. During two years, thirty patients are evaluable for study: 17 patients received prostate SBRT, 5 LDR brachytherapy, 7 moderately hypofractionated IMRT, and one with conventionally fractionated IMRT. Data was collected at median intervals of 30, 95, and 294 days after therapy. Median bowel QOL scores at first, second and third follow-up time points for EPIC-26 bowel score 100, 95, and 100 respectively. For EPIC-26 urinary incontinence score was were 100, 90, and 90. There was no difference across survey participants for EPIC-26 bowel (p=0.52) or urinary bother (p=0.58) or AUA-SI total score (p=0.44) across all time points. Dosimetric variables were not associated with any decline in QOL scores at these time points. We achieved favorable dosimetry for all patients. Within the SBRT patients, dose to 50% of the rectum was a median of 656 cGy (IQR 727) and dose to 50% of the bladder was 215 cGy (245) which far exceeds the recommended constraints. Dose to 25% of the rectum for SBRT patients was 1153 (IQR 869). Within the hypofractionated group dose to 50% of the rectum the median was 2301(IQR 519). A hydrogel spacer results in relatively favorable dosimetry for all prostate radiotherapy modalities given to patients with favorable-intermediate or low risk prostate cancer. Hydrogel spacer placement also portends stable good long-term QOL outcomes.