Ionizing Radiation

Harmful effects of radiation

Two harmful effects are distinguished:

1. Deterministic effects; the likelihood and severity of the effects are dose-dependent. From a certain threshold dose, the body is no longer able to repair the radiation-induced cellular damage; think of red skin after prolonged radioscopy.  Under the threshold dose, no effect occurs; above the threshold dose the severity of the effect increases with the radiation dose.
   These are effects in the short term after high radiation dose. 
2. Stochastic (risk-bound) effects; the likelihood of these effects occurring depends on the dose. The higher the exposure, the higher the risk that the effect will occur. There is no threshold dose.
   These are potential effects in the long term after exposure to a low dose. All radiation to which someone is exposed in his/her life is added up. This can be compared with the concept of number of pack-years in smokers.

The primary radiation risk is the development of cancer.
Much is known about the effect of acute high radiation doses (cancer, red skin, hair loss etc).  Think particularly of examinations related to the nuclear bomb explosions in Hiroshima & Nagasaki in Japan. 
Unfortunately, we still have much to learn about the long-term risks following exposure to low-dose radiation. In addition to environmental factors that have their impact, it takes several decades for cancer to develop (long incubation time). What it comes down to is that it is difficult to distinguish 'spontaneously’ developed tumors from tumors resulting from exposure to low-dose radiation. 

IRCP estimate the risk of radiation-induced cancer in low dose and low dose rate at 5.5% per Sv. 
So this is 0.0055% per mSv (1 Sv = 1000 mSv).

For your reference, some data:

• The mean dose for CT tests varies from 2 – 20 mSv.
• General ‘basic risk’: +- 1 in 6 women will develop breast cancer at some point in their lives (= 16.7%). 
• Death risk due to smoking is 0.005% per 100 cigarettes.  One could say that the risk of 1 cigarette about equals 0.01 mSv. If someone smokes 2000 cigarettes a year (= about 2 packs/week), this will 'expose’ this person to 20 mSv annually.  

In view of the uncertain long-term effects of radiation, rules have been formulated in the Netherlands:

• Per capita dose limit:  1 mSv per year (above the natural background radiation). 
• Dose limit at hospital site perimeter:  < 0.1 mSv annually.
• Dose limit for radiology worker:   20 mSv annually (calculation: 30 working years = 600 mSv = 0.6 Sv). 

Note: there is no official dose limit for radiation in medical diagnostics (radiology and nuclear medicine) and medical treatment (intervention radiology, radiotherapy and nuclear medicine). 

Primary risk groups include pilots (cosmic radiation), intervention radiologists/intervention cardiologists and professions in industrial applications such as isotope production.  Using personal dosimeters (fig. 2), information is obtained on professional exposure to ionizing radiation. This is documented in the National Dose Registration and Information System (NDRIS).

Children

Children are more sensitive to radiation than adults. This is because children have many replicating cells. Consequently, DNA errors and/or changes may occur relatively more frequently, which could lead to the development of cancer. Additionally, the child has more time to develop cancer (long incubation time!) compared to someone of 70 years old. 
A correct indication is essential to minimize the child's radiation burden.  In each X-ray/CT test, it must be considered whether the question cannot be answered using an imaging technique without ionizing radiation (such as ultrasound or MRI).