Pregnancy and radiation

Pregnancy and medical radiation

English PowerPoint presentation about pregnancy and radiation in medical applications, based on ICRP-publication 84.

The Dutch Decree on Basic Safety Standards Radiation Protection contains among others a number of regulations for protecting the unborn child. Taking into account the number of students, the male-female ratio and the age distribution of the group of dentistry students who enroll each year in the training for Radiation Protection Officer - dentistry - basic, one should not wonder that there is often a person who worries about her child because of the dose received during the laboratory course.

In the following an estimate is made of the maximum radiation dose that possibly can be received during the laboratory course. The result will be compared with a number of situations well-known from daily life. After a careful study of the course booklet, everybody should be able to verify these estimates.

From these estimates it follows that the radiation risk during the health physics course is negligible. The imposed effective dose is even smaller than the fluctuations in time and space of the background radiation.

But... it is quite understandable that a mother worries about the health of her child. Fortunately, during the laboratory course people work in groups, and it is always possible that a non-pregnant member of the group manipulates the radioactive sources, while the pregnant one makes notes and carries out the necessary calculations at a safe distance (inverse quadratic law!). In this way, the already small dose can be further reduced.

Regulations

According to the Decree on Basic Safety Standards Radiation Protection, the effective dose received by any employee as a consequence of his work may not exceed 1 mSv per annum. In addition,  the effective dose received by the unborn child during the pregnancy as a consequence of the work of the mother, may not exceed 1 mSv.

For comparison reasons: the effective dose received by each individual person in the Netherlands due to natural radiation sources (radon, potassium, cosmic radiation) amounts to 1 à 2 mSv per annum.

Laboratory course

The strongest radioactive source that is handled during the laboratory course, contains about 150 MBq ⁶⁰Co. The source constant of this radionuclide is Γ = 0.36 μSv h^-1 MBq^-1 m². The working distance during the experiment is 1 meter or more, and the handling time is 2 hours or less. The effective dose received during the experiment is, therefore, certainly less than 0.36 × 150 × 2 = 100 μSv, which is about 10% of the annual dose due to natural radiation.

Because this is a strongly collimated source, the calculation mentioned above applies only to a person who is exposed to the direct beam. By stepping aside, one can easily further reduce the dose by several orders of magnitude. The other radioactive sources handled during the laboratory course contain an activity that is 10000 times less and can, therefore, safely be neglected.

Dental surgery

The average effective dose received by a patient when an intra-oral X-ray picture is taken, amounts to a few μSv at most(see: RIVM - stralingstoepassingen in de tandheelkundige praktijk ). This dose can almost entirely be attributed to direct irradiation of one or more of the six salivary glands  - with a tissue weighting factor w_salivary = 0.01 - and because the thyroid - with a tissue weighting factor w_thyroid = 0.04 - is exposed to X-radiation scattered from the jaw. The equivalent dose for the thyroid amounts, therefore, to less than H_thyroid = 1 / 0.04 = 25 μSv per X-ray picture.

The distance between uterus and jaw is more than 10 times as large as the distance between thyroid and jaw. According to the quadratic law, the equivalent dose for the uterus and, therefore, the effective dose for the unborn child is more than 10² = 100 times smaller than the thyroid dose of the mother. In other words: the effective dose of the unborn child is much less than 1 μSv per X-ray picture. This is about equal to the effective dose received from natural background during a single day.

Skiing in the alps

The natural background radiation varies in time (fluctuating sun activity), location (varying soil conditions), and altitude. For example, the dose rate at an altitude of 1500 m is 60 nSv/h compared to 30 nSv/h at sea level. At an altitude of 10 km - the average cruising altitude during a transatlantic flight - the dose rate is even 3 μSv/h!

During a ski vacation at an altitude of 1500 meters the extra effective dose amounts to 14 × 24 × (60-30) = 10000 nSv = 10 μSv.