PURPOSE: A single-phase 3 trial has demonstrated that prostate radiation therapy with a focal, intraprostatic "microboost" can improve disease control without an overall increase in toxicity. It is unclear how these results generalize to other treatment schedules and protocols. METHODS AND MATERIALS: A systematic search of PubMed and the Cochrane review was performed for studies published on or before September 1, 2023. A random-effects meta-analysis was used to pool the cumulative incidence of grade ≥2 (≥G2) acute and late genitourinary (GU) and gastrointestinal (GI) toxicity. Heterogeneity was assessed, and the association of trial-level covariates with toxicity was examined via the subgroup analyses and meta-regression. Odds ratios (ORs) for dose metrics were reported per Gy equivalent dose in 2Gy per fraction (EQD2). RESULTS: Thirty-eight patient cohorts were included. The pooled estimate of the cumulative incidence of ≥G2 acute and late GU toxicity was 25.3% (95% CI, 19.1%-32.8%) and 21.1% (95% CI, 16.7%-26.3%), respectively. Late ≥G2 GI toxicity was less frequent, estimated at 5.6% (95% CI, 3.5%-8.7%) and 6.9% (95% CI, 4.6%-10.1%), respectively. Subgroup factors associated with at least one ≥G2 toxicity category were treatment technique, imaging used for boost volume definition, intrafraction motion management, trial phase, and toxicity grading. Rectal D CONCLUSIONS: The utilization of a microboost seems tolerable across treatment protocols
however, subgroup factors, including the use of intrafraction motion management and the type of imaging modality used, may influence the probability of toxicity. Attention to rectal D