From the Guidelines
A high ionizing radiation dose is generally considered to be above 1 Sievert (Sv). Doses between 1-2 Sv can cause radiation sickness with symptoms like nausea, vomiting, and fatigue, while exposures above 2 Sv are considered very high and potentially lethal. At 4-5 Sv, the mortality rate reaches 50% without medical treatment, and doses exceeding 8-10 Sv are almost always fatal even with intensive medical care. For context, natural background radiation exposes humans to about 0.001-0.003 Sv annually, while a single chest X-ray delivers only about 0.00002 Sv. Radiation doses are considered high based on their biological effects, as ionizing radiation damages cellular DNA and other structures, with higher doses overwhelming the body's repair mechanisms and causing acute radiation syndrome. The effects of radiation exposure are cumulative over a lifetime, which is why radiation workers have strict annual exposure limits of 0.05 Sv to minimize long-term health risks.
Some key points to consider when evaluating ionizing radiation doses include:
- The equivalent dose for a given type of radiation is defined by using a weighting factor specific to that type of radiation, which in the case of X- and gamma-rays is equal to 1, and can be higher for other types of ionising radiation 1.
- The effective dose is the weighted sum of the equivalent dose in a series of tissues or organs, using weighting factors specific to each of the tissues on the basis of their susceptibility to the onset of radio-induced cancers 1.
- The risk of developing a malignant neoplasm during one’s lifetime is around 42% (i.e. in the course of their lifetime almost one out of every two people will suffer a malign neoplasm), and the additional risk of developing a malignant tumour following exposure to ionising radiation is known as “lifetime attributable risk” (LAR) 1.
- Exposure to 1 mSv (the average national per capita dose originating from execution of diagnostic procedures for adults) involves a LAR of developing a tumour equal to 5 cases per 100,000 adults, with risk depending on age, it diminishes to 1–2 cases per 100,000 for people over 60 and increases to 10–15 cases per 100,000 for children 1.
It's worth noting that the most recent and highest quality study on this topic is from 2019, which provides a comprehensive review of the risks associated with ionizing radiation exposure 1. This study highlights the importance of considering the cumulative effects of radiation exposure over a lifetime and the need for strict annual exposure limits to minimize long-term health risks.
From the Research
Definition of High Ionizing Radiation Dose
A high ionizing radiation dose is generally considered to be above 1 Gy (1000 mSv) [ 2 ]. At doses above 1 Gy, cell killing and modification can cause deterministic effects such as skin burns and bone marrow depression.
Effects of High Ionizing Radiation Doses
- At doses above 2 Gy, acute whole body penetrating gamma irradiation can result in varying degrees of acute radiation sickness [ 2 ].
- Doses above 10 Gy are usually lethal due to combined organ injury [ 2 ].
- High doses of ionizing radiation can increase the risk of subsequent cancer in the exposed individual [ 3 ].
Comparison of Ionizing Radiation Doses
- The average annual effective dose from background radiation is about 3 mSv [ 4 ].
- Medical uses of radiation, such as computed tomographic examinations and interventional procedures, can have average effective doses ranging from 2-70 mSv [ 4 ].
- The risk of cancer induction varies widely across different tissues, but the risk of fatal radiation-induced cancer for a general population following chronic exposure is about 5% Sv(-1) [ 2 ].