Radiation Exposure from X-rays and CT Scans for Ankle Injuries

Radiation issues

Hello Dr.
Wang, I sprained my ankle at the end of August.
On September 5th, I went to the hospital for an X-ray of my left ankle (one frontal and one lateral view).
The doctor suspected a fracture from the X-ray and ordered a CT scan of my left foot, which confirmed the fracture.
During a follow-up on September 19th, I had another X-ray (frontal and lateral), and the doctor said there was no malalignment and advised me to return for another X-ray in a month.
I'm a bit concerned about the frequency of the imaging.
1) Could you please tell me the approximate radiation dose in millisieverts (mSv) for an ankle X-ray and a CT scan? I couldn't find the radiation dose for foot imaging on the radiation dose chart from the Atomic Energy Council.
For reference, a chest CT is 7 mSv, a cardiac CT is 16 mSv, and a lumbar spine X-ray is 1.5 mSv.
If we assume the foot CT is approximately between the chest and cardiac CT doses, it would be (7+16)/2 = 10.15 mSv.
Given that the recommended annual limit is not to exceed 10 mSv, am I already over the limit, and should I wait longer before returning for an orthopedic follow-up?
2) Is it possible to request a lead apron when getting an X-ray at the hospital? I did not wear one during the two ankle X-rays, but I was offered one when I visited the dentist.
Can I ask to wear one?
Thank you for your response, Dr.
Wang!

Mr. Chen, 30~39 year old female. Ask Date: 2020/09/28

Dr. Wang Yifen reply Radiology

Hello,
1.
According to the American Society of Radiologic Technologists, the radiation dose for a single examination of the extremities is approximately 0.001 millisieverts, while the radiation dose for a full-body CT scan is about 21 millisieverts.
The International Commission on Radiological Protection (ICRP) report 103 states that doses below 100 millisieverts (whether single or multiple) do not cause clinically significant functional impairment.
Following your doctor's advice to undergo radiation-related examinations is based on the consideration that the health benefits outweigh the radiation risks.
If you have concerns, it is advisable to communicate with your physician before proceeding with the examination.
Do not avoid examinations out of fear of radiation, as this may lead to missed opportunities for disease treatment.
2.
The American Association of Physicists in Medicine (AAPM) issued a position statement on April 2, 2019, recommending the cessation of the use of patient gonadal and fetal shielding in routine X-ray diagnostic imaging.
This is because such shielding may obscure organ structures or interfere with the automatic exposure control of imaging systems, potentially increasing the patient's radiation dose.
Therefore, with current imaging technology, the use of shielding (lead aprons) is not recommended.

For reference, please visit https://www.aapm.org/org/policies/details.asp?id=468&type=PP.

Wishing you safety and health.

Reply Date: 2020/09/28

More Info

When considering the radiation exposure from X-rays and CT scans, especially in the context of an ankle injury, it is essential to understand the associated risks and benefits of these diagnostic tools.
1. Radiation Dose from X-rays and CT Scans: According to the American College of Radiology and the Radiological Society of North America, the radiation dose from a standard X-ray of the ankle is approximately 0.001 mSv (millisieverts) per view. Since you had two views (anterior-posterior and lateral), the total dose from the X-ray would be about 0.002 mSv. In contrast, a CT scan of the ankle typically delivers a dose of around 1 to 10 mSv, depending on the specific protocol used and the machine's settings. For your case, if we assume a mid-range dose of about 5 mSv for the ankle CT, the total radiation exposure from both the X-ray and the CT scan would be approximately 5.002 mSv.

2. Annual Radiation Exposure Limits: The general recommendation for annual occupational exposure for radiation workers is 50 mSv, while the public is advised to limit exposure to about 1 mSv per year from artificial sources. However, medical imaging is often justified when the benefits of diagnosis and treatment outweigh the risks of radiation exposure. In your case, the total exposure from the imaging studies you underwent is significantly below the recommended limits, and the risk of developing radiation-induced cancer from such low doses is exceedingly low.

3. Concerns About Cumulative Exposure: You mentioned a concern about exceeding the recommended annual limit of 10 mSv. Based on the calculations, your total exposure from the ankle X-ray and CT scan is well below this threshold. It is crucial to remember that the risk of harm from radiation is cumulative over time, but the doses from individual diagnostic procedures are typically low. If you require further imaging in the future, it is advisable to discuss the necessity of each procedure with your healthcare provider, ensuring that the benefits of obtaining the information needed for your treatment outweigh the risks.

4. Use of Lead Shields: Regarding your question about wearing lead aprons during X-ray examinations, the current guidelines from organizations such as the American Association of Physicists in Medicine (AAPM) suggest that lead shielding for patients is not necessary for most X-ray examinations. This is because the radiation dose from a single X-ray is low, and the use of lead aprons can sometimes interfere with the imaging process, potentially leading to increased radiation exposure due to adjustments in exposure settings. However, if you feel more comfortable wearing one, you can certainly ask the radiology staff if it is available for your procedure.

In summary, the radiation exposure from your ankle X-ray and CT scan is minimal and well within safe limits. It is always prudent to have open discussions with your healthcare provider regarding the necessity of imaging studies and any concerns you may have about radiation exposure. Your health and safety are paramount, and ensuring that you receive appropriate care while minimizing unnecessary risks is a collaborative effort between you and your medical team.

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