3599 - Real World Data Analysis of Biochemical Recurrence after Primary Radiotherapy for Prostate Cancer: Propensity Matched Comparison of Patients with Hydrogel Rectal Spacing vs. No Spacing

Purpose/Objective(s):

Placement of rectal hydrogel spacers prior to prostate cancer radiotherapy is associated with reduced rectal toxicity and improved quality of life. However, the impact of spacing on oncological outcomes has not been established. The objective of this exploratory study was to assess the association between rectal hydrogel spacer use prior to radiotherapy for prostate cancer and biochemical recurrence rates as an early indication of oncological outcomes.

Materials/Methods:

This retrospective cohort study utilized electronic health records data compiled by Truveta Data from a collective of U.S. healthcare systems. The analysis included patients who had placement of rectal hydrogel spacer prior to primary external beam radiation therapy (EBRT) for prostate cancer treatment between 2016-2022. A control group of men who underwent primary EBRT for prostate cancer without rectal spacing was matched using 1:2 propensity score matching based on age, race, ethnicity, presence of local or lymphatic invasion, presence of metastatic disease, androgen deprivation therapy (ADT) category, and year of primary EBRT. Multivariable regression was used to compare rates of biochemical recurrence (as defined by the Phoenix criteria of 2ng/mL over PSA nadir) = 2 years after primary EBRT, controlling for the matched variables and radiation modality.

Results:

On initial screening, 36,866 patients who underwent primary EBRT for prostate cancer were identified for inclusion. Of these, 259 patients with rectal hydrogel spacers had = 2 years of PSA follow-up after primary EBRT, with a mean PSA follow-up period of 43 months [24 – 103 months]. For these patients, mean age was 69.5 years [SD 7.1 years], 8.1% (n = 21) were Black, 20.1% (n = 52) received combination ADT therapy, and a majority received intensity-modulated radiation therapy (IMRT) [64.5% (n = 176)]. Biochemical recurrence rates were significantly less in patients who received rectal spacers compared to their matched control counterparts (5% vs 11.4%, AD -6.4%, 95% CI [-10.2% - -2.6%]). On multivariable regression, adjusting for matching criteria and radiation modality, patients with rectal spacer placement had significantly lower odds of biochemical recurrence compared to those who did not receive rectal spacing (adjusted OR 0.4, 95% CI [0.24-0.67]). In this sensitivity analysis, spacer placement remained significant, but radiation modality was not.

Conclusion:

This initial exploratory study suggests that in addition to reduction of gastrointestinal toxicity from EBRT, placement of rectal spacers prior to radiotherapy may also improve oncological outcomes. Further study of this association is needed to both confirm and understand the mechanism of improved cancer control observed here with rectal hydrogel spacer use.