Focal Boost in Prostate Cancer Radiotherapy: A Review of Planning Studies and Clinical Trials

SIMPLE SUMMARY: By delivering escalated doses to biologically defined sub-volumes within a target, focal boost radiotherapy is expected to enable an elevated tumor control without an increase in toxicity in prostate cancer. Evidence for the efficacy and variability of this approach has been summarized and evaluated to support future focal boost radiotherapy studies and trials. For 34 planning studies and 35 clinical trials, published during 2013–2023, the methodology of treatment planning, dosimetric outcomes, and clinical efficacy were summarized and evaluated in this review. The challenges reported in the reviewed studies and their potential solutions are highlighted to serve future focal boost radiotherapy studies and trials. ABSTRACT: Background: Focal boost radiotherapy was developed to deliver elevated doses to functional sub-volumes within a target. Such a technique was hypothesized to improve treatment outcomes without increasing toxicity in prostate cancer treatment. Purpose: To summarize and evaluate the efficacy and variability of focal boost radiotherapy by reviewing focal boost planning studies and clinical trials that have been published in the last ten years. Methods: Published reports of focal boost radiotherapy, that specifically incorporate dose escalation to intra-prostatic lesions (IPLs), were reviewed and summarized. Correlations between acute/late ≥G2 genitourinary (GU) or gastrointestinal (GI) toxicity and clinical factors were determined by a meta-analysis. Results: By reviewing and summarizing 34 planning studies and 35 trials, a significant dose escalation to the GTV and thus higher tumor control of focal boost radiotherapy were reported consistently by all reviewed studies. Reviewed trials reported a not significant difference in toxicity between focal boost and conventional radiotherapy. Acute ≥G2 GU and late ≥G2 GI toxicities were reported the most and least prevalent, respectively, and a negative correlation was found between the rate of toxicity and proportion of low-risk or intermediate-risk patients in the cohort. Conclusion: Focal boost prostate cancer radiotherapy has the potential to be a new standard of care.