Important Considerations After Two Days of X-Ray Imaging - Radiology

Dr. Xie Cangtai reply Radiology

---

Dear NFS: Hello, in our living environment, radiation is almost ubiquitous, with some being naturally occurring and others being man-made.
There are two pathways for radiation exposure: external exposure and internal exposure.
External exposure primarily comes from cosmic rays, terrestrial radiation, radiological diagnostic treatments (such as X-ray examinations), or from working in radiation-related occupations.
Internal exposure can occur due to contamination in the workplace, contamination of the worker's body, or through the injection of radioactive substances during nuclear medicine examinations.
The routes of internal exposure include inhalation, ingestion, skin contact, or through wounds, with inhalation being the most common route of contamination.

The biological effects of radiation refer to the impact of ionizing radiation, which carries energy, when it strikes human tissues.
The energy from the radiation is transferred to the cells, and upon absorbing high-energy radiation, cells may undergo ionization or excitation, potentially leading to the breaking of molecular chemical bonds and damaging cellular functions.
The health effects of radiation on the human body are generally classified into two categories: stochastic effects and deterministic effects.
When the human body receives a dose exceeding a certain threshold in a short period, many cells may die or become irreparable, resulting in symptoms such as fatigue, nausea, vomiting, skin erythema, hair loss, and a significant decrease in white blood cells and lymphocytes.
As the dose increases, the severity of symptoms escalates, potentially leading to death; this situation is referred to as deterministic effects.
Typically, deterministic effects occur only when the dose exceeds a certain level; otherwise, they do not manifest.
According to the radiation protection safety standards established by the Republic of China on January 30, 2003, the dose limits for the general public are as follows: 1.
The effective equivalent dose in one year must not exceed 1 millisievert (mSv).
2.
The equivalent dose to the lens of the eye in one year must not exceed 15 mSv.
3.
The equivalent dose to the skin in one year must not exceed 50 mSv.
The term "personal dose" refers to the total dose received from both external and internal exposure, excluding doses from background radiation and medical exposure.
To prevent the occurrence of deterministic effects and to reduce the incidence of stochastic effects, radiation practices must adhere to the following regulations: 1.
The benefits must outweigh the costs.
2.
All exposures should be reasonably minimized after considering economic and social factors.
3.
Personal doses must not exceed the specified limits in these standards.
To control stochastic effects, dose limits are expressed in terms of effective equivalent dose.
To prevent deterministic effects, dose limits are expressed in terms of equivalent dose.
Equivalent dose is defined as the absorbed dose in human tissues multiplied by the radiation weighting factor, which accounts for the potential biological damage caused by radiation to tissues and organs.
Its unit is the sievert (Sv), abbreviated as Sv, defined as: HT (Sv) = D (Gy) × Q, where one thousandth of a sievert is a millisievert (mSv), and the radiation weighting factor for X-rays is 1.

For instance, a chest X-ray typically delivers a dose of about 0.1 mSv to the chest tissue.
A lumbar spine X-ray can deliver a dose 20 to 80 times that of a chest X-ray.
Long-term studies of survivors of the atomic bomb in Japan indicate that individuals exposed to low doses (approximately below 250 mSv) show no clinical symptoms, and the incidence of leukemia or other solid cancers is similar to that of the general population.
However, for radiation safety reasons, the International Commission on Radiological Protection (ICRP) has made a conservative and important assumption: any exposure to radiation, regardless of the dose, carries a risk of inducing cancer and adverse genetic effects, with no threshold dose value.
Furthermore, the probability of cancer or adverse genetic effects is proportional to the dose received (linear relationship); the higher the dose, the greater the risk, which is referred to as stochastic effects.
X-ray examinations are classified as low-dose radiation procedures, and current domestic regulations do not specify or limit the number of X-ray examinations or the amount of radiation that the public can receive in a year for medical purposes.
This is because the doses from typical X-ray examinations are very low, and the irradiated areas are localized rather than whole-body or large-area exposures.
Additionally, low-dose radiation is not expected to cause harm to human tissues.
Moreover, the benefits of early disease diagnosis from low-dose radiation outweigh the risks; however, this should not lead to neglecting or demanding unnecessary examinations from physicians.
In conclusion: 1.
There are no immediate or direct effects.
2.
To reasonably minimize stochastic effects, reduce exposure or consult with a physician.
3.
There is no need for excessive worry; maintaining a healthy lifestyle is sufficient.
(The article is partially derived from relevant literature on radiation, books, and regulations.)

---

Reply Date: 2004/12/09