Question: How will I know if the external beam radiation therapy worked?
Answer: After external beam radiation therapy for prostate cancer, the best method of following the patients is a combination of blood PSA determinations. PSA's short for prostatic-specific antigen, and the normal blood level can be an indicator of persistence of prostate cancer. But a combination of PSA in the blood and rectal exam -- digital rectal exam of the prostate, which is a simple clinical procedure in the doctor's office -- gives us a very high level of indication of how well we are doing.
It should be noted that PSA blood levels can take a long time -- up to a two-year time lag between completing radiation therapy and going down to levels that are low enough that we are satisfied that we have cured the patient. So people should not be scared if immediately after -- or even a year to a year and a half later -- the PSA is still coming down slowly but surely.