A PET-CT scan for cancer involves exposure to radiation from two sources: the radioactive tracer used in the PET portion and the X-rays used in the CT portion. The amount of radiation a patient receives depends on several factors, including the type and dose of radiotracer, the CT scan settings, and whether any dose-reduction techniques are applied.
The PET part uses a small amount of a radioactive substance called a radiotracer—most commonly fluorine-18 fluorodeoxyglucose (18F-FDG). This tracer emits positrons that interact with electrons in your body to produce gamma rays detected by the scanner. The typical injected activity is around 5 to 15 millicuries (mCi), which corresponds roughly to an effective radiation dose of about 5 to 7 millisieverts (mSv). This is roughly equivalent to two or three years’ worth of natural background radiation exposure.
The CT component adds additional radiation because it uses X-rays to create detailed anatomical images. Depending on whether it’s a low-dose CT done mainly for attenuation correction or a full diagnostic-quality CT with contrast, this can add anywhere from about 2 mSv up to around 10 mSv or more. When combined, most standard clinical whole-body PET-CT scans deliver an effective dose typically between approximately 7 and 20 mSv.
Newer technologies have helped reduce these doses significantly. For example, advanced long axial field-of-view PET/CT scanners allow lower doses of radiotracers while maintaining image quality and can shorten scan times as well. Some studies have shown that using reduced tracer doses—around two-thirds or even half what was previously standard—and optimized scanning protocols can cut overall radiation exposure without compromising diagnostic accuracy.
To put this into perspective:
– A chest X-ray delivers about 0.1 mSv.
– A typical abdominal CT alone might be around 8–10 mSv.
– Natural background radiation averages about 3 mSv per year depending on location.
So while a PET-CT does expose patients to more ionizing radiation than many other imaging tests, it provides critical information by combining metabolic activity visualization with precise anatomical detail that no single modality offers alone.
Because cancer diagnosis and treatment planning rely heavily on accurate staging and monitoring response at both structural and cellular levels, physicians weigh these benefits against risks carefully before recommending scans. Radiation doses are kept as low as reasonably achievable through tailored protocols based on patient size, clinical indication, scanner capabilities, and latest guidelines.
After injection of the radioactive tracer during a PET scan portion:
– Most radioactivity decays quickly; over half disappears within hours.
– Patients are advised to drink plenty of fluids afterward so their bodies clear out remaining radioactivity faster through urine.
Repeated scans increase cumulative exposure but remain justified when necessary for optimal management since untreated cancer poses far greater health risks than these controlled imaging exposures.
In summary: A typical cancer-related whole-body PET/CT scan exposes patients roughly between **7–20 millisieverts** total from combined radiotracer injection plus computed tomography X-rays—with ongoing advances steadily lowering those numbers—providing invaluable insight into tumor metabolism alongside anatomy for guiding personalized treatment decisions safely within accepted medical standards.
