radiographs. CT scans alone, which account for half the medical imaging dose to the public, are estimated to be responsible for 0.4% of current cancers in the United States, and this may increase to as high as 1.5-2% with 2007 rates of CT usage; however, this estimate is disputed. Other nuclear medicine techniques involve the injection of radioactive pharmaceuticals directly into the bloodstream, and radiotherapy treatments deliberately deliver lethal doses (on a cellular level) to tumors and surrounding tissues. It has been estimated that CT scans performed in the US in 2007 alone will result in 29,000 new cancer cases in future years. This estimate is criticized by the American College of Radiology (ACR), which maintains that the life expectancy of CT scanned patients is not that of the general population and that the model of calculating cancer is based on total-body radiation exposure and thus faulty. Occupational In accordance with ICRP recommendations, most regulators permit nuclear energy workers to receive up to 20 times more radiation dose than is permitted for the general public. Higher doses are usually permitted when responding to an emergency. The majority of workers are routinely kept well within regulatory limits, while a few essential technicians will routinely approach their maximum each year. Accidental overexposures beyond regulatory limits happen globally several times a year. Astronauts on long missions are at higher risk of cancer, see cancer and spaceflight. Some occupations are exposed to radiation without being classed as nuclear energy workers. Airline crews receive occupational exposures from cosmic radiation because of reduced atmospheric shielding at altitude. Mine workers receive occupational exposures to radon, especially in uranium mines. Anyone working in a granite building, such as the US Capitol, is likely to receive a dose from natural uranium in the granite. Accidental Nuclear accidents can have dramatic consequences to their surroundings, but their global impact on cancer is less than that of natural and medical exposures. The most severe nuclear accident is probably the Chernobyl disaster. In addition to conventional fatalities and acute radiation syndrome fatalities, nine children died of thyroid cancer, and it is estimated that there may be up to 4,000 excess cancer deaths among the approximately 600,000 most highly exposed people. Of the 100 million curies (4 exabecquerels) of radioactive material, the short lived radioactive isotopes such as 131I Chernobyl released were initially the most dangerous. Due to their short half-lives of 5