So, i am not sure where you got those numbers, but here is a great info-graphic for you with all the numbers you could possibly want to know:
https://www-tc.pbs.org/wnet/need-to-.../radiation.png Some key points - - A chest X-Ray averages at 0.02 mSv - A chest CT scan averages at 5.8 mSv - A worker's YEARLY limit is 50mSv - The lowest one YEAR dose clearly linked to cancer risk (not guaranteed cancer, just a measurable risk) is 100 mSv Aside from all that.. you are treating radiation as if it were a gas tank.. once its full, you are done for good, which is not how it works. Ionizing radiation, *IN LARGE ENOUGH DOSES* can damage cells and DNA structures, which can be a cause of cancer (or simply death in a large enough dose). So long as your DNA has not been damaged (thus replicated into new cells), there will be a point where your body would be.... unaware.. that you have ever encountered additional radiation (again, refer to the chart, and remember we ALL get background dosing, well in excess of total 25mSv by the time we are 10).