The operating specifications are very strict regarding the dose of radiation received each time, and a single PET-CT examination generally does not cause cancer. As a more effective and safer PET-CT examination, the radiation dose produced is generally within the acceptable range of the human body and will not cause harm to the human body, much less cause cancer because of a single PET-CT examination. Radiation doses cause biological effects in humans have deterministic effects with certain thresholds, such as large doses in a short period of time or multiple radiation doses in a short period of time in a row that exceed a certain threshold before cancer or some biological effect is produced.