How does radiation to the breast in a lactating woman affect milk production?

Additional information regarding radiation and the effect on lactation:

There is no evidence that breast fed babies are at increased risk of cancer. For women who have had radiation to the breast, in a published study, 80% had decreased lactation volume reported. Most women could produce mild, (55.6...

We generally use medication to suppress lactation during RT as otherwise it can cause symptomatic engorgement.