Re-irradiation to the Prostate using stereotactic body radiotherapy (SBRT) after initial definitive Radiotherapy – A systematic review and Meta-analysis of recent trials

Background There is increasing data on re-irradiation to the prostate using stereotactic body radiotherapy (SBRT) after definite radiotherapy for prostate cancer. There has been increasing evidence on prostate re-irradiation using a C-arm LINAC or a MR LINAC in the last years. We therefore conducted this systematic review and meta-analysis on prostate re-irradiation including studies published from 2020-2023 to serve as an update on existing meta-analysis. Methods We searched the Pubmed and Embase databases in October 2023 with queries including combinations of “repeat”, “radiotherapy”, “prostate”, “re-irradiation”, “reirradiation”, “re treatment”, “SBRT”, “retreatment”. Publication date was set to be from 2020 to 2023. There was no limitation regarding language. We adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations. After data extraction, heterogeneity testing using I2. Afterwards a random effects model with a restricted maximum likelihood estimator was used for estimating the combined effect. Funnel plot asymmetry was assessed visually and using Eggers test to estimate the presence of publication and/or small study bias. Results 14 publications were included in the systematic review. The rates of acute ≥ grade 2 (G2) GU and GI toxicities reported in the included studies range from 0.0-30.0% and 0.0-25.0% respectively. For late ≥G2 GU and GI toxicity, those values are 4.0-51.8% and 0.0-25.0%. The pooled rate of acute GU and GI toxicity ≥G2 were 13% (95% CI: 7-18%) and 2% (95% CI: 0-4%). For late GU and GI toxicity ≥G2 the pooled rates were 25% (95% CI: 14-35%) and 5% (95% CI: 1-9%). The pooled 2-year biochemical recurrence-free survival was 72% (95% CI: 64-92%). Conclusions SBRT in the re-irradiation of radiorecurrent prostate cancer is overall safe and effective also when applied with a C-arm Linac or an MR Linac. Further prospective data are warranted. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.