The radiation dose of an ordinary chest X-ray is about 0.1mSv, which is equivalent to 10 days of background irradiation, and the cancer dose is negligible. However, the radiation dose of CT scan is far more than tens of times compared to chest X-ray. When scanning, the radiation exposure varies from one part of the scan to another, and some parts need to be scanned extensively or have multi-phase enhancement scan, the radiation dose will increase exponentially, generally between 3-20mSv. As the machine continues to evolve and the scan parameters are set, the doctor will minimize the radiation. Nowadays, it is also possible to perform a double low-dose scan, which not only does not affect the quality of the image, but is also able to reduce the radiation dose to a great extent. In short, don’t worry excessively when you need a CT scan, because some tests are necessary and are not as harmful to the patient as you might think.