From the Guidelines
Undergoing 6 CT scans and one PET-CT scan within 6 months is not safe in terms of radiation exposure, as it exceeds typical radiation safety guidelines for the general population, with a potential cumulative dose of 21-85 mSv, which is significantly higher than the annual background radiation exposure of about 3 mSv. This amount of radiation exposure raises concerns about the potential long-term cancer risk, particularly for younger patients. According to the study by Boone et al 1, there is evidence of adverse effects of radiation exposure at doses greater than 100 mSv, including an incremental increase in the incidence of various types of cancer. While the study by the American College of Radiology 1 notes that the cancer risk from medical imaging is small but real, it also emphasizes that radiation-induced cancers typically do not occur until 1 or 2 decades or longer after exposure.
Some key points to consider:
- A typical CT scan delivers about 1-10 millisieverts (mSv) of radiation per exam, while a PET-CT can deliver 15-25 mSv 1.
- The cumulative dose of 21-85 mSv from 6 CT scans and one PET-CT scan is significant compared to the annual background radiation exposure of about 3 mSv.
- The long-term cancer risk from medical imaging is higher for younger patients.
- Alternative imaging methods like MRI or ultrasound may be appropriate for some follow-up exams to minimize future radiation exposure.
- Lower-dose CT protocols can be used to reduce radiation exposure.
- Each scan should be medically necessary to justify the radiation exposure.
It is essential to discuss with your doctor the potential risks and benefits of undergoing multiple CT scans and PET-CT scans within a short timeframe, and to explore alternative imaging methods or lower-dose protocols to minimize radiation exposure. As noted by Boone et al 1, advances in knowledge and technology have improved the ability to estimate radiation dose and risk, and to optimize the use of CT scanning. Therefore, it is crucial to weigh the medical benefits of these scans against the potential radiation risks and to take steps to minimize exposure whenever possible.
From the Research
Radiation Exposure from CT and PET-CT Scans
- The total effective dose to the patient from a PET/CT procedure is approximately 10 mSv, with the major part coming from internal irradiation due to radiopharmaceuticals (approximately 6-7 mSv) and a minor part from the CT scan (approximately 2-4 mSv) 2.
- A study estimated that the mean effective dose from CT scans in patients with lymphoma was 39.3 mSv during the treatment period and 53.2 mSv during the surveillance period, with 17 of 76 patients having total cumulative doses greater than 100 mSv 3.
Safety of Undergoing Multiple Scans
- The estimated cancer risk from CT and PET/CT scans in patients with lymphoma was found to be low, with a mean increase in estimated cancer risk of 0.40% and the greatest estimated risk to any one patient being 1.19% 3.
- There is a growing concern about the detrimental consequences of ionizing radiation from CT scans, and anxiety from the perceived risks can deter referring physicians from ordering clinically indicated CT scans and patients from undergoing medically necessary exams 4.
Communication of Radiation Risks
- Patients and providers appear to be more aware of radiation dose from CT scans than they were in the past, but discussion of CT scan radiation exposure and associated risks only occurs sometimes and may actually occur less frequently than perceived by emergency providers 5.
- A collaborative approach between emergency physicians and radiologists is suggested to help explain the risks of radiation to patients who may have concerns about getting medical imaging 6.