I agree with what everyone else has said; the importance of getting even a minimal bit of exercise. Also, stay hydrated! that was the single biggest problem I had during rads, and every time I wound up being admitted, it was due to dehydration.
Rads alone is tortuous; for me it was FAR worse than the surgery was, and I had a LOT of surgery. Some days it was getting by minute by minute, no question.
But...you will get through it. Set a goal tomorrow to get up, get dressed by yourself, and walk from your front door to the street and back, twice. Reward yourself with a liter of water.

Do the same thing the next day, or push it up to three round trips. You'll be quite surprised at how helpful it is.
Much luck!