While gamma radiation is, on the above basis, understood to have some benefits, the effects of beta and alpha radiation as are known to be quite destructive to cell tissue. While these forms of radiation are less common to be exposed to and easier to protect against than gamma radiation, I strongly doubt they've any positive effect at reducing the risk of cancer. The one known exception may be exposure to Iodine-131, a beta particle emitter, because it collects in the thyroid. While high doses will destroy the thyroid and stop iodine from collecting in the thyroid, low doses will collect there and the beta particles released by the iodine will cause thyroid cancer.