Jen,
The only way to tell is when your blood chemistry is in normal limits. Pay attention to RBC and WBC levels. They do a histogram of mine every 6 months when I am tested and everything now is within normal limits. It took almost 2 years for everything to be within normal range. That doesn't mean it takes 2 years for the immune system to recover but it does take a long time. It takes 120 days just for the red blood cells that were destroyed in radiation to recover. I waited for over 4 months before I started back out in public and I was very careful.

One thing I just discovered is that red blood cells tend to travel in clumps in the larger arteries so this may explain the large amount of lowered red cell count from blood damaged passing through the carotids.

If you bruise easily or bleed a lot then you probably have neutropenia and need talk to your MO.

To help stimulate your immune system: 1. Execise, 2. Eat good foods and a complete balanced diet with lots of fruits and vegetables. 3. Get adequate rest 4. Stay hydrated - 2-3 liters a day (that inludes water in your food) 5. Follow all of the first post advice about prevention.

The rest will come naturally. Your immune system can only be "stimulated" and the above suggestions are the best and most effective way to do it.

IT IS NOT POSSIBLE to boost your immune system. Don't waste your money on worthless ptoducts, making phony and unsubstantiated claims (including vitamins -multivitamins are ok Vitamin C megadosing is NOT recommended it is best to get your "C" from citrus fruits).

Make sure you get a biannual TSH test as well if you had radiation.