Looks like you are 8 months out of RT. At one point my white cell count was in the 0.x decimals, where it should have been 4.0 minimum (not sure what the test evaluated). My GP said it was common for RT patients, but gave me severe warnings about
avoiding crowds as much as possible, and especially people who were obviously ill (colds, flu and the like).
My RT ended late June 2010. In October they re-ran the WBC test, because it was so low. By April 2011, it was back up to 50% of the minimum side of the range. Now in October 2011, it is slightly above the minimum.
I did not take anything to boost it. Just seems to be coming back on its own with time, as the GP expected.