Why is testosterone replacement not advisable after brachytherapy for prostate cancer?

Growth Factor: Testosterone stimulates growth and multiplication of prostate cells - both normal and cancerous ones. So if any cells survive the brachytherapy, they will grow faster in the presence of testosterone, and be more likely to form a large mass or spread to other parts of the body before being detected.

TRT post radiation: Hypogonadism following prostate radiation is a serious issue that affects biological changes and quality of life. The main fear is prostate cancer recurrence as testosterone stimulates the prostate and possibly dormant prostate cancer. Controversy exists regarding management with limited clinical data. Some institutions a advocating trt with caution and close psa f/u. Sarosdy mf et al cancer 2007.