Radiation Dose from CT Scans: What Patients Should Know

How can one determine the radiation dose received during a CT scan?

Hello, Dr.
Hsu.
I would like to ask again, the radiation dose (in mSv) from different CT machines and different examination locations should vary significantly.
How can patients find out the radiation dose for a specific CT scan? Will this information be included in the report or medical record? I noticed in the materials you provided that the radiation dose for abdominal scans is quite high.
Why do some hospitals still perform full-body CT screenings? Isn't the total radiation dose extremely high for a single scan? Thank you.

CT, 0~9 year old female. Ask Date: 2015/06/01

Dr. Yang Jinghua reply Radiology

Dear CT,
Hello.
Continuous CT medical radiation affects all living organisms on Earth, whether they like it or not, and has been a part of our existence since ancient times.
Humanity exists on the continuum of biological evolution, and our bodies can be considered products of a long history of coexisting with radiation.
In Taiwan, each person is exposed to an average of about 2 millisieverts (mSv) of natural background radiation per year.
All radiation exposure from medical imaging is assessed, and the risk of radiation harm is very low.
If the purpose of the procedure aligns with the justification for medical exposure, such as diagnosing a disease or facilitating treatment, the benefits outweigh the risks of radiation.
Therefore, it is advisable to consider repeating a head CT scan in consultation with your physician.
However, if the scan is solely for administrative purposes (such as a health check), it is not recommended to perform CT scans or other examinations with higher radiation exposure.
Based on your description, the estimated medical radiation doses you have received are as follows:
1.
A single head X-ray is approximately 0.1 mSv; eight X-rays total about 0.8 mSv.
2.
A chest X-ray is approximately 0.02 mSv.
3.
An abdominal CT scan averages about 8 mSv.
4.
A head CT scan averages about 2 mSv.
The total effective radiation dose from the above is approximately 10.82 mSv, which is equivalent to the natural background radiation dose received over eight years.
According to the International Commission on Radiological Protection (ICRP 103), exposure to 1 mSv of radiation carries a risk of cancer and genetic harm of about 4 in 100,000.
Therefore, your exposure of 10.82 mSv corresponds to a risk of approximately 4.3 in 10,000, which is negligible compared to the 28% cancer risk from natural background radiation among the population (the proportion of cancer among the top ten causes of death).
However, based on the principles of justification and optimization for medical radiation exposure, it is recommended to first consider non-radiation-based examinations, such as ultrasound, for medical diagnostic purposes.
Please discuss whether you can adopt this recommendation with your physician.
Additionally, regarding the amount of radiation (in mSv) each patient receives after a CT scan, it can only be estimated based on factors such as the energy emitted by the equipment and the area irradiated (number of slices, patient thickness).
Therefore, it does not represent the actual effective dose received by the patient (in mSv) and is not suitable for reporting or documentation in medical records.
In the future, advancements in equipment may allow for direct detection of the actual effective dose received by patients (in mSv), enabling patients to know their effective dose immediately after completing the examination.
Whole-body CT scans are screening examinations, and the equipment and imaging conditions used differ from those of standard diagnostic equipment, typically operating in low-dose mode.
Consequently, the radiation dose received by patients will be lower than the sum of the doses from the aforementioned individual examinations.
Wishing you peace and health.
Sincerely,
Dr.
Ching-Hua Yang
Director, Department of Radiology
Taoyuan Hospital, Ministry of Health and Welfare

Reply Date: 2015/06/01

More Info

Understanding the radiation dose from CT scans is a crucial aspect of patient care, especially as concerns about radiation exposure continue to grow. CT (computed tomography) scans are invaluable diagnostic tools that provide detailed images of the body's internal structures, but they do involve exposure to ionizing radiation. Here’s what patients should know about radiation doses from CT scans, how to understand them, and the associated risks.

Radiation Dose from CT Scans
The radiation dose from a CT scan is typically measured in millisieverts (mSv). The amount of radiation a patient receives can vary significantly based on several factors, including the type of CT scanner used, the specific body part being scanned, the scanning protocol, and the patient's size. For instance, a standard abdominal CT scan can expose a patient to approximately 8-10 mSv, while a chest CT may deliver around 5-7 mSv. In comparison, a single chest X-ray typically delivers about 0.1 mSv.

How to Know Your Radiation Dose
After a CT scan, patients often wonder how to find out the exact radiation dose they received. Generally, the radiation dose is not explicitly stated on the report or in the medical records. However, the CT machine does record parameters such as the CT Dose Index (CTDI) and the Dose-Length Product (DLP), which can be used to estimate the effective dose in mSv.
The effective dose can be calculated using the DLP value, which is a product of the CTDI and the length of the scan. For example, if a CT scan has a DLP of 400 mGy·cm and the conversion factor for the body part scanned is 0.015 mSv·mGy^-1·cm^-1, the effective dose would be approximately 6 mSv. Unfortunately, this information is not always included in the final report, so patients should feel free to ask their healthcare providers for clarification on their specific radiation exposure.

Risks Associated with CT Scans
While it is true that CT scans expose patients to higher doses of radiation compared to traditional X-rays, the associated risks are generally considered low, especially when the scans are medically justified. The International Commission on Radiological Protection (ICRP) suggests that the risk of developing cancer from radiation exposure below 100 mSv is minimal. For context, the lifetime risk of developing cancer from a single CT scan is estimated to be about 1 in 10,000 to 1 in 20,000, depending on the dose received and individual risk factors.

The Role of Full-Body CT Scans
Concerns about the high radiation dose from full-body CT scans are valid. However, many hospitals and clinics utilize low-dose protocols for screening purposes, which can significantly reduce the radiation exposure. Full-body scans are often marketed as preventive measures, but they should be approached with caution. The decision to undergo such a scan should be based on a thorough discussion with a healthcare provider, weighing the potential benefits against the risks.

Conclusion
In summary, understanding the radiation dose from CT scans is essential for informed decision-making. Patients should inquire about their specific radiation exposure, especially if multiple scans are performed in a short period. While the risks associated with CT scans are generally low, they should not be taken lightly. It is crucial to ensure that any imaging study is warranted and that alternative imaging modalities, such as ultrasound or MRI, are considered when appropriate. Always consult with your healthcare provider to discuss the necessity of the scan and any concerns regarding radiation exposure.

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