Dose limits do not apply for radiation exposure of patients, since the decision to use radiation is justified depending upon the individual patient situation. When it has been decided that a medical procedure is justified, the procedure should be optimized. This means that the conditions should achieve the clinical purpose with the appropriate dose. Safe limits are determined only for the staff and not for patients.
'Ten day rule' was postulated by ICRP for woman of reproductive age. It states that "whenever possible, one should confine the radiological examination of the lower abdomen and pelvis to the 10-day interval following the onset of menstruation." The original proposal was for 14 days, but this was reduced to 10 days to account for the variability of the human menstrual cycle. In most situations, there is growing evidence that a strict adherence to the "ten-day rule" may be unnecessarily restrictive. When the number of cells in the conceptus is small and their nature is not yet specialized, the effect of damage to these cells is most likely to take the form of failure to implant, or of an undetectable death of the conceptus; malformations are unlikely or very rare. Since organogenesis starts 3 to 5 weeks post-conception, it was felt that radiation exposure in early pregnancy couldn't result in malformation. The main risk is that of abortion if the radiation exposure results in death of the conceptus. It requires a foetal dose of more than 100 mGy for this to occur. Based on this, it was suggested to do away with the 10-day rule and replace it with a 28-day rule. This means that radiological examination, if so justified, can be carried throughout the cycle until a period is missed. Thus the focus is shifted to a missed period and the possibility of pregnancy. If there is a missed period, a female should be considered pregnant unless proved otherwise. In such a situation, every care should be taken to explore other methods of getting needed information by using non-radiological examinations.
Occasionally, a patient will not be aware of a pregnancy at the time of an X ray examination, and will naturally be very concerned when the pregnancy becomes known.
In such cases, the radiation dose to the fetus/conceptus should be estimated, but only by a medical physicist/ radiation safety specialist experienced in dosimetry. The patient can then be better advised as to the potential risks involved. In many cases there is little risk, as the irradiation will have occurred in the first 3 weeks following conception. In a few cases the conceptus will be older and the dose involved may be considerable. It is, however, extremely rare for the dose to be high enough to warrant advising the patient to consider terminating the pregnancy.
If a calculation of radiation dose is required in order to advise the patient, the radiographic factors should be noted if known. Some assumptions may be made in the dosimetry, but it is best to use actual data. The patient's date of conception or date of LMP (last menstrual period) should also be determined.
Medically indicated diagnostic studies remote from the fetus (e.g. radiographs of the chest or extremities) can be safely done at any time during pregnancy if the equipment is in proper working order. Commonly, the risk of not making the diagnosis is greater than the radiation risk involved.
If an examination is typically at the high end of the diagnostic dose range and the fetus is in or near the radiation beam or source, care should be taken to minimize the dose to the fetus while still making the diagnosis. Tailoring the examination and examining each radiograph as it is taken until the diagnosis is achieved and then terminating the procedure can do this.
It is unlikely that radiation from diagnostic radiological examinations will result in any deleterious effects on the child, but the possibility of a radiation-induced effect cannot be entirely ruled out. The effects of exposure to radiation on the conceptus depend on the time of exposure with respect to the date of conception and the amount of absorbed dose. The following description is for scientific professionals and the effects described are to be seen only under the situations mentioned. It does not imply that these effects shall occur with doses encountered in common examinations, as they are quite small. For further details, please see ICRP 84.
Yes. There will be many situations where the benefit of performing the procedure is much greater than any small possible harm that might arise from the radiation exposure. However, as always with any medical exposure, each particular procedure must be clinically justified, including in this situation taking into account when the procedure needs to occur and the anticipated radiation dose to the foetus. Once justified, due care is taken to optimise how the procedure is performed so as to minimise radiation exposure to the foetus, consistent with achieving the desired clinical outcome. The radiation exposure to foetus predominantly arises from scattered radiation within the patient. Some of the main methods for minimising the dose to the foetus include: restricting the X-ray beam size to being as small as is necessary for the clinical purpose; choosing the direction of the primary beam so that it is as far away from the foetus as possible; selecting appropriate exposure factors; and ensuring that the overall exposure time is as small as possible. For well performed procedures, estimated foetal doses are typically quite small, and well below the level of concern for radiation effects, but calculations of dose by a knowledgeable medical physicist is desirable. As a final comment, putting a lead apron on the table to cut down any primary beam from the X-ray tube reaching the foetus has very little effect, but it can be reassuring to the patient and staff and thus is recommended provided the use of the apron does not compromise the performance of the procedure.
According to ICRP 84, termination of pregnancy at foetal doses of less than 100 mGy is not justified based upon radiation risk. At foetal doses between 100 and 500 mGy, the decision should be based upon the individual circumstances.
The issue of pregnancy termination is undoubtedly managed differently around the world. It is complicated by individual ethical, moral, and religious beliefs as well as perhaps being subject to laws or regulations at a local or national level. This complicated issue involves much more than radiation protection considerations and require the provision of counseling for the patient and her partner.
At foetal doses in excess of 500 mGy, there can be significant foetal damage, the magnitude and type of which is a function of dose and stage of pregnancy.
For more information, consult ICRP 84.
The gonads are radiosensitive organs in the human body. The threshold radiation dose for permanent sterility in men is 3500 - 6000 mGy, and for women 2500 - 6000 mGy. As diagnostic X ray examinations involve small doses (see Table 1), they imply no risk of sterility.
|Conventional X ray examinations||Mean (mGy)||Maximum (mGy)|
|Chest||< 0.01||< 0.01|
|Skull||< 0.01||< 0.01|
|Thoracic spine||< 0.01||< 0.01|
|Fluoroscopic examinations||Mean (mGy)||Maximum (mGy)|
|Barium meal (UGI)||1.1||5.8|
|Computed tomography||Mean (mGy)||Maximum (mGy)|
|Head||< 0.005||< 0.005|
A pregnant worker can continue working in an X ray department as long as there is reasonable assurance that the foetal dose can be kept below 1 mGy during the pregnancy. In interpreting this recommendation, it is important to ensure that pregnant women are not subjected to unnecessary discrimination. There are responsibilities for both the worker and the employer. The first responsibility for the protection of the conceptus lies with the woman herself, who should declare her pregnancy to management as soon as the condition is confirmed. The following recommendations are taken from ICRP 84:
Radiation doses to occupationally exposed staff working with radiological equipment are generally low and it is unlikely that the equivalent dose limit recommended by the ICRP (see Table II) will be approached. However, for some fluoroscopic examinations there is a potential for higher radiation doses to staff. During interventional radiology procedures, particular radiation protection problems arise from the extended fluoroscopy times and from the use of certain radiological equipments, which may not have lead rubber protective curtains. Consequently, the implications of the ICRP recommendations on the radiation exposure of the fetus of staff performing fluoroscopy procedures should be assessed.
TABLE II. ICRP 60 RECOMMENDATIONS
|Assumed radiation risks||ICRP Publication 60|
|Workers||4.0 x 10-2 Sv-1 for fatal cancer
0.8 x 10-2 Sv-1 for non-fatal cancer detriment
0.8 x 10-2 Sv-1 for severe genetic effects
|Members of the public||5.0 x 10-2 Sv-1 for fatal cancer
1.0 x 10-2 Sv-1 for non-fatal cancer
1.3 x 10-2 Sv-1 for severe genetic effects
|Embryo-foetus||Not specifically stated|
|Occupational dose limits||ICRP Publication 60|
|Based on stochastic effects||50 mSv annual effective dose limit and 100 mSv in 5 y cumulative effective dose limit|
|Based on deterministic effects||150 mSv* equivalent dose to lens of eye and 500 mSv annual equivalent dose limit to the skin, hands and feet|
|Public dose limits||ICRP Publication 60|
|Based on stochastic effects||1 mSv annual effective dose limit and, if needed, higher values provided that the annual average over 5 y does not exceed 1 mSv|
|Based on deterministic effects||15 mSv annual effective dose limit to lens of eye and 50 mSv annual equivalent dose limit to skin, hands, and feet|
*After its meeting on April 21, 2011 the ICRP issued a statement recommending an equivalent dose limit to the lens of the eye of 20 mSv per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv.
Patients who have received diagnostic studies while pregnant are often alarmed because of emotional perceptions surrounding radiation. The health professionals should advise patients about the steps that will be taken for risk assessment and provide appropriate information regarding the risk associated with diagnostic (and therapeutic) radiation exposure during pregnancy. The following points should be considered: