Radiation sources from PET-CT scans

PET-CT scans are advanced medical imaging techniques that combine positron emission tomography (PET) and computed tomography (CT), widely used for cancer diagnosis, staging, and evaluation of treatment efficacy. However, this examination is inevitably accompanied by radiation exposure, the source of which is mainly divided into two parts: the radioactivity of the developer and the X-ray of the scanning device.pet ct scan邊間好

First, PET scans require the use of radioactive contrast agents (e.g., fluorodeoxyglucose, FDG) that annihilate electrons in the human body and emit positrons that produce γ rays. This radioactive material has a short half-life (FDG is about 110 minutes), but care should be taken to avoid prolonged contact with pregnant women and children after the test.

Secondly, the CT scan part relies on X-rays to penetrate human tissue, and the scanning dose varies greatly from location to location. For example, a single whole-body PET-CT radiation dose is about 10 to 25 millisieverts (mSv), which is equivalent to a dose of several hundred chest X-rays. Some medical institutions in Hong Kong offer low-dose CT options that can reduce radiation dose by 30%-50%, making them suitable for patients who require multiple follow-up examinations.

The choice is remarkableIt is necessary to pay attention to whether the facility is equipped with modern equipment (for example, digital PET-CT) that can further reduce the radiation dose. meantimeIt is relatively low and does not contain radiation, so it can be used as an alternative to initial screening for liver lesions.

Effects of radiation on the human body

The effects of radiation on the human body can be divided into deterministic effects (short-term exposure at high doses) and random effects (long-term accumulation at low doses). PET-CT radiation doses usually fall into the latter category and may increase the lifetime risk of cancer, but the probability is very low (about 0.05%-0.5%).

Sensitive individuals should pay special attention.

• child: Cells divide actively and are 3 to 5 times more radiosensitive than adults
• pregnant woman: It can affect fetal development, especially in the first trimester
• Cancer patients: Excess doses may accumulate in multiple tests

According to data from the Hong Kong Health Bureau, the average annual exposure to medical radiation in the region is about 3.5mSv/person, of which diagnostic tests account for 88%. In contrast, a single PET-CT has a higher dose but is worth performing when the clinical benefit outweighs the risks (e.g., early detection of metastases).肝超聲波檢查收費

Radiation dose of PET-CT scan in Hong Kong

According to the Hong Kong Association of Radiologists 2022 guidelines, the radiation dose for common imaging tests is as follows:

All PET-CT centers in Hong Kong follow the International Atomic Energy Agency (IAEA) safety standards, with annual radiation dose limits of 50 mSv (staff) and 1 mSv (public). It is worth noting thatAlthough there is no radiation, the resolution of deep lesions is limited, and appropriate tools should be selected according to the condition.

How to reduce radiation risk

Effectively controlling PET-CT radiation risk requires a multifaceted approach.

Technical level

Choosing a PET-CT machine with "Time Flight Technology" (TOF) can reduce developer usage by 30%. Some institutions offer low-dose CT protocols, especially for underweight individuals and children.

Protective measures

• Drink plenty of water after the test to speed up the metabolism of the contrast agent (excrete more than 50% within 6 hours)
• Sensitive areas are protected by lead clothing (thyroid, gonads, etc.)
• Family members in the same row should keep a distance of more than 2 meters or use a mobile lead screen

Check the frequency

The International Commission on Radiological Protection (ICRP) recommends that cancer patients should not undergo PET-CT more than 3-4 times a year. Some private hospitals in Hong Kong offer "radiation passport" services to consolidate the cumulative dose of various examinations for patients.

If you need to contact us, refer to the equipment certification list issued by the Hong Kong Medical Accreditation Council (CHKS), and give priority to institutions with third-generation digital PET-CT.

Assessing the Risks and Benefits of PET-CT Scanning

Clinical decision-making should follow the principle of "reasonable reduction" (ALARA), taking a common application scenario in Hong Kong as an example.

Cancer screening

The positive predictive value of routine screening in asymptomatic people is only 5%-10%, which is not recommended as a medical examination item. However, for high-risk groups of lung cancer (e.g., 30 pack-year smoking history), low-dose CT is still the first choice.

Treatment evaluation

In lymphoma patients, the treatment plan is changed by 30% due to PET-CT results during treatment, and the risk of radiation is much lower than the cost of incorrect treatment.

Points of communication between doctor and patient:

• Explicitly inform of alternatives (e.g., MRI).Comparison)
• Explaining the possibility of false positives/negatives
• Provide a specific value of radiation dose

According to data from the Hong Kong Cancer Registry, the 5-year survival rate of early-stage cancers (such as stage I lung cancer) can reach 80%, and the moderate use of PET-CT is of irreplaceable value in improving diagnostic accuracy. chooseIn addition to the price factor, the institution's quality control and radiation protection system should also be considered.

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