1) The combination of amount and period of exposure is what is important with radiation dosage. Evidence seems to be that regular small dosages are not all that bad for you, but sudden large dosages can be. Small doses might even, if your a rat, allow you to improve survival of large doses. One interesting question here is do repeated small doses increase cancer risk cumulatively? The problem here is that I suspect you would need such a large sample size, due to the small effects, that this is pretty much impossible to test in practice.
2) Sudden large dosages are actually not necessarily all that bad for you unless they cause Acute Radiation Syndrome(ARS). Evidence for this was from studies on Hiroshima and Nagasaki where the extra cancer death's between 1950 and 2000 caused by the nuclear radiation was approx 0.7%. ARS takes affect somewhere between 2000 and 4000 mSv. Hiroshima had an average dose of 160mSv. No extra cancers were found in doses under 100mSv. As a comparison, a CT scan is between 5-10 mSv
3) Living cells are rather good at healing themselves from radiation damage. Radiation treatments work, at least partly, by damaging the cell faster then cells can heal.
4) The currently advised radiation limits are based around keeping the limits as low as reasonably possible rather than what the human body can endure with minimal risk
5) There really isn't all that much reliable human data as big radioactive events are rare.
6) The problem with a lot of data around long term after affects in areas like Chernobyl is that it is unreliable (according to UN and WHO).
7) I haven't verified any of this
Anyone know anything to contradict this?