Radiation Dose and Distance in Dental X-rays: Key Concerns

Q: Radiation Dose and Distance in Dental X-rays: Key Concerns

Hello： <br>1. <br>Regarding the placement of X-rays in a full-mouth X-ray machine： X-rays are produced when the X-ray tube is energized, releasing energy that is converted into X-rays due to the high-voltage electric field. <br>Therefore, X-rays are emitted from the X-ray tube of

Questions about radiation dose and distance?

I have read articles on E-net regarding similar issues, but the answers did not alleviate my concerns, so I am asking again to see if there are clearer answers.
I have seen articles elsewhere mentioning that radiation dose is related to distance.
It seems that the closer the distance, the greater the harm.
Once, when I had a full-mouth X-ray, the nurse seemed to have not adjusted the distance properly, and when the machine was rotating, one side was close to my right cheek.

1.
I would like to ask how a full-mouth X-ray machine operates.
Is it a U-shaped machine that surrounds the top of the head? When the machine starts to operate, where is the X-ray radiation emitted?
2.
If the X-ray emission is in a U-shape, does it emit radiation from both sides or only one side?
3.
If it is only one side, is it sufficient to maintain distance from the X-ray emission side?
4.
If both sides emit radiation, how much will the radiation dose I receive increase?
5.
An article on E-net regarding a similar question mentioned that the machine would stop if it malfunctioned.
However, the article's question indicated that the images produced were blurry, while mine were not.
I would like to know if the statement about the machine stopping during a malfunction means that as long as the machine operates until the examination is completed, the effective dose of radiation will be the same, and that being too close to the face will not result in a higher radiation dose?
6.
During this period, due to issues with my body and teeth, I have had approximately four full-mouth X-rays and over twenty bitewing and periapical X-rays in just two months.
I also had one intravenous pyelogram and one abdominal X-ray.
I would like to know if these doses in such a short time will have a significant impact?

Jin Jin, 30~39 year old female. Ask Date: 2018/11/26

Dr. Wang Yifen reply Radiology

Hello:
1.
Regarding the placement of X-rays in a full-mouth X-ray machine: X-rays are produced when the X-ray tube is energized, releasing energy that is converted into X-rays due to the high-voltage electric field.
Therefore, X-rays are emitted from the X-ray tube of the machine.
The location where the X-ray tube is installed is where the X-rays are emitted.
In a full-mouth X-ray machine, the X-ray tube is located on one side in a "U" shape, while the other side is the image receptor.
Since the dental arch is curved, the machine rotates while simultaneously capturing images, and the received images are processed by a computer to create a full-mouth X-ray film.
2.
Regarding the relationship between radiation dose and distance: The amount of radiation is inversely proportional to the square of the distance.
Therefore, the farther one is from the X-ray machine, the lower the radiation dose.
For "non-patients," such as staff or accompanying family members, the farther they are from the X-ray machine, the lower the exposure to X-rays.
However, for "patients," when the X-ray tube is close to the target (short distance), the irradiation area becomes smaller, allowing for a lower X-ray dose to meet diagnostic requirements and reducing scatter radiation to surrounding non-target areas.
Conversely, when the X-ray tube is farther from the target (long distance), the irradiation area increases, requiring a higher X-ray dose to meet diagnostic needs and increasing scatter radiation to surrounding non-target areas.
Therefore, for "patients," to achieve good image quality and reduce radiation dose, the X-ray tube is positioned as close to the target as possible, minimizing the distance to the irradiated area.
The distance between the X-ray tube and the receptor in a full-mouth X-ray machine is usually fixed, and the distance from the X-ray tube to the target is limited, so patients will not experience significant differences in radiation exposure due to the machine being too close or too far from the face.
3.
Regarding the brief exposure to X-rays: According to the American Society of Radiologic Technologists, the radiation dose for a single full-mouth X-ray is approximately 0.01 millisieverts, while a single bitewing X-ray is about 0.005 millisieverts.
The radiation dose for intravenous urograms is about 3 millisieverts, and abdominal X-rays are approximately 0.7 millisieverts.
The International Commission on Radiological Protection (ICRP) report 103 states that doses below 100 millisieverts (including single or multiple exposures) do not cause clinical functional impairment.
The radiation dose you are currently receiving is not expected to have adverse effects; however, the effects of radiation on the human body can accumulate.
It is advisable to discuss the necessity of the X-ray examination with your physician before undergoing the procedure, and to make efforts to reduce unnecessary radiation exposure.

Wishing you safety and health.

Reply Date: 2018/11/26

More Info

Understanding the concerns surrounding radiation exposure from dental X-rays is crucial, especially for patients who may undergo multiple imaging procedures in a short time. Let's address your questions systematically.

1. Operation of Panoramic X-ray Machines: A panoramic X-ray machine operates by rotating around the patient's head in a semi-circular (or "M" shaped) path. The X-ray tube emits radiation from one side of the machine, while the opposite side contains the image receptor. The X-rays are directed towards the dental arch, capturing a comprehensive view of the teeth, jaws, and surrounding structures in a single image. The radiation is emitted in a controlled manner to minimize exposure while maximizing image quality.

2. Radiation Emission: In a typical panoramic X-ray setup, radiation is primarily emitted from one side of the machine at a time. The design is such that the X-ray beam is focused on the area of interest (the dental arch) while the receptor captures the image on the opposite side. Therefore, only one side of the machine is actively emitting radiation during the exposure.

3. Distance and Exposure: If the X-ray emission is from a single side, maintaining a safe distance from that side is indeed beneficial. However, the machine is designed to minimize unnecessary exposure to surrounding tissues. The closer the X-ray source is to the target area (in this case, your teeth), the lower the radiation dose required to produce a diagnostic image. This is why the machine is positioned close to the patient's face during the procedure.

4. Increased Radiation from Dual Emission: If both sides of the machine were to emit radiation simultaneously (which is not typical for panoramic X-rays), the exposure would theoretically increase. However, in standard practice, only one side is active at any given time, so the radiation dose remains within safe limits as determined by regulatory standards.

5. Machine Malfunction and Radiation Dose: When a machine is functioning correctly, the radiation dose is calibrated to ensure that it is within safe limits for diagnostic purposes. If a machine were to malfunction, it might either not emit radiation or emit it incorrectly, potentially leading to a higher dose. However, modern machines are equipped with safety features that prevent excessive exposure. If your image was clear and not blurry, it indicates that the machine was functioning properly during your exposure.

6. Cumulative Radiation Exposure: Regarding your concern about the frequency of X-ray examinations, it's important to note that the radiation doses from dental X-rays are relatively low. For instance, a full-mouth series of X-rays typically delivers about 0.01 mSv per exposure, while a single bitewing X-ray delivers about 0.005 mSv. In contrast, a CT scan of the abdomen can deliver approximately 10 mSv. The International Commission on Radiological Protection (ICRP) states that doses below 100 mSv are unlikely to cause significant health effects. Therefore, while cumulative exposure does matter, the doses you mentioned (4 full-mouth X-rays and additional dental images) are unlikely to pose a significant risk, especially when performed for necessary medical reasons.

In summary, while it is wise to be cautious about radiation exposure, the benefits of necessary imaging procedures often outweigh the risks. If you have ongoing concerns about your dental health or the necessity of repeated imaging, it is advisable to discuss these with your dentist or healthcare provider. They can provide personalized recommendations based on your specific situation and health needs. Always prioritize open communication with your healthcare team regarding any procedures you undergo.

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