When should the seminal vesicles be included in the target volume in prostate radiotherapy?

External beam radiotherapy to the prostate and seminal vesicles as a radical treatment for prostate cancer can result in a significant dose being delivered to the rectum. This can be reduced if the target volume includes the prostate only. Using a Medline search, published studies are reviewed to show that the risk of seminal vesicle involvement can be accurately predicted using readily available pre-treatment parameters. We recommend when to exclude the seminal vesicles from a target volume, and the proportion of seminal vesicles that should be included in a target volume in higher risk patients.