Background radiation equivalent time BRET value corresponding to a dose of radiation is the number of days of average background dose it is equivalent to. It is calculated from the equivalent dose in sieverts by dividing by the average annual background radiation dose in Sv, and multiplying by 365: The definition of the BRET unit is apparently unstandardized, and depends on what value is used for the average annual background radiation dose, which varies greatly across time and location. The 2000 UNSCEAR estimate for worldwide average natural background radiation dose is 2.4 mSv (240 mrem), with a range from 1 to 13 mSv. A
Radiation hormesis "error-prone nonhomologous end joining (NHEJ) repair in postirradiation cellular response, argues strongly against a DNA repair-mediated low-dose threshold for cancer initiation". Recent research observed that DSBs caused by CAT scans are repaired within 24-hours and DSBs maybe more efficiently repaired at low doses, suggesting the risk ionizing radiation at low doses may not by directly proportional to the dose. However, it is not known if low dose ionizing radiation stimulates the repair of DSBs not caused by ionizing radiation "i.e." a hormetic response. Radon gas in homes is the largest source of radiation dose for most individuals and it is