ABSTRACT

Prostate-specific antigen (PSA) is the most sensitive measure of cancer recurrence and progression after definitive treatment of prostate cancer. After radiation therapy, PSA levels should fall slowly over 18-24 months as prostate cancer cells die from the lethal effects of radiation. The serum half-life of PSA after radiation therapy has been estimated to be 1.9 months. This is contrary to the precipitous drop in PSA levels after a successful prostatectomy, where the serum PSA half-life has been estimated to be 3.2 days. Biochemical recurrence, also known as PSA failure, is defined by the American Society of Therapeutic Radiation Oncology (ASTRO) as three consecutive rises in serum PSA with each measurement separated by 3-4 months. It is important to document three consecutive rises in PSA before diagnosing cancer recurrence, because transient rises in PSA may be seen with asymptomatic prostatitis after radiation which is know as “PSA bounce”. While PSA bounce is seen more often after brachytherapy than external beam radiotherapy, it has been reported with both modalities.