His spokesperson said he was now having radiation therapy and hormone treatment “as part of a treatment plan”.
Mr Biden previously said the cancer had “a Gleason score of 9 (Grade Group 5) with metastasis to the bone” (meaning it had spread from the prostate).
The radiation treatment is expected to last five weeks and marks a new stage in his care. He has already been taking a pill form of hormone medication.
Mr Biden, who turns 83 next month, is said to be “doing well”.
Last month, Mr Biden also had a skin cancer treatment known as Mohs surgery. A large bandage on his forehead was visible in public appearances at that time.
Revealing his condition earlier this year, the ex-president said he was diagnosed after seeing a doctor about urinary symptoms.
A statement said he had a “more aggressive form of the disease” but that it appeared to be “hormone-sensitive which allows for effective management”.
According to Cancer Research UK, a Gleason score of 9 means the cancerous cells “look very abnormal” and the disease is “likely to grow quickly”.
Prostate cancer is very common among men of Mr Biden’s age but many have a low-risk form of it that only requires monitoring.
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