Microboost in Localized Prostate Cancer: Analysis of a Statewide Quality Consortium

Purpose

Prospective trials have reported isotoxicity and improved oncologic outcomes with external beam radiation therapy (EBRT) microboost to a dominant intraprostatic lesion. There is often variability in the rate of adoption of new treatments, and current microboost practice patterns are unknown. We leveraged prospectively collected data from the multicenter Michigan Radiation Oncology Quality Consortium to understand the current state of microboost usage for localized prostate cancer.

Materials and Methods

Men with intermediate- and high-risk prostate adenocarcinoma treated with curative-intent radiation between October, 26, 2020, and June, 26, 2023, were included across 26 centers. Demographic-, tumor-, and treatment-related data along with DICOM files were prospectively collected. Microboost intent was prospectively documented and DICOM-confirmed. Multivariable analyses were used to evaluate associations with microboost receipt, and mixed-effects modeling evaluated facility-level variation.

Results

Most patients received EBRT without brachytherapy (71%, n = 524/741). Of those, a minority received an EBRT microboost (10%, n = 53/524) at a subset of sites (27%, n = 7/26), without a change in rate over the study period (P = .62). Grade group 4/5 (odds ration [OR] = 2.35; 95% confidence interval [CI]: 1.02-5.28), magnetic resonance imaging planning (OR = 6.34; 95%CI: 2.16-27.12), and fiducial marker/rectal spacer placement (OR = 2.59; 95% CI: 1.14-6.70) were associated with microboost use. Significant facility-level variability was present (minimum 0%; 95% CI: 0.0-10.7 to maximum 71%; 95% CI: 55.5-83.2, unadjusted, P < .0001). Median boost volume was 20.7cc, and median boost D98% was 94.4 EQD2Gy. Compared with non-microboost cases, intermediate doses to rectum in the microboost cohort were increased (eg, V20Gy [EQD2] of 53.8% vs 36.5%, P = .03). However, the proportion exceeding NRG/RTOG bladder/rectal constraints was low and not significantly different between cohorts.

Conclusions

Despite prospective data demonstrating its benefit, EBRT microboost was used within a diverse statewide quality consortium in only 10% of cases at 27% of sites with significant facility-level heterogeneity. Concerted efforts are required to understand current barriers to microboost utilization, and results from trials such as PIVOTALboost (ISRCTN80146950) are eagerly awaited.