A “scoping” review of prostate brachytherapy and immune responses

Purpose Whether prostate brachytherapy (BT) results in opportunistic biological changes that can improve clinical outcomes is not well studied. We sought to investigate the impact of prostate BT on the immune system. Materials and Methods A scoping review was performed using PubMed/Scopus for papers published between 2011-2021. Search terms were “brachytherapy” AND “immune” AND “prostate”. A total of 81 records were identified and 6 were selected for further review. Results 2 low-dose-rate BT papers (n=68) evaluated changes in the peripheral blood following I-125 monotherapy. Both showed significant increases in peripheral CD3+ and CD4+ T cells post-BT. One also demonstrated significant increases in Treg subsets up to 150 days post-BT. 4 high-dose-rate (HDR) studies (n=37) were identified, and all were done in combination with EBRT. The largest study (n=24) showed a single 10 Gy fraction of HDR converted 80% of “cold” tumors into an “intermediate” or “hot” state, based on a tumor inflammation signature when comparing a pre-BT biopsy to one prior to a second HDR fraction. Conclusion Prostate BT can invoke an immune activating phenotype; however, changes in immunosuppressive cells are also seen. Additional data is needed to understand how to promote synergy between BT and the immune system.