Due to their premature age, very low weight patients at birth need to be treated for respiratory or digestive diseases in neonatal intensive care units.
Incidentally, such a medical practice involves several exposures to ionising radiation since frequent radiological examinations such as chest or abdomen are being performed during their medical follow-up. Furthermore, those patients who have clinical complications may require a complementary period of hospitalisation lasting, in few cases, several months. Additional X-ray examinations, such as barium studies, intravenous urography (IVU) or even CT scanners, can also be carried out during this period.
With the view of establishing a baseline framework for a possible epidemiological study and in order to assess the potential increased risk among the population of premature babies due to these cumulative exposures, a dosimetric study was carried out in collaboration with the intensive care unit and radiology departments at the Trousseau Hospital in Paris in 2002.
Entrance surface doses were measured by thermoluminescent dosimeters stuck on patient’s skin at the centre of the incident beam while radiographs were being taken. Effective and bone marrow doses were thus derived from these measurements for three categories of baby’s weight (1, 2 and 3 kg).
Individual cumulative doses received over the period of stay in the intensive care unit were estimated, for each premature baby born in 2002, taking into account the number of radiographs which they underwent.
For the referenced year, 125 premature babies (70 boys and 55 girls) were treated in the intensive care unit. Among them, 28% were highly premature babies (born before week 32).
Results of the dosimetry study showed that, even if average doses per radiograph were relatively low (average entrance dose, effective dose and bone marrow dose of 70µGy, 25µGy, 6µGy, respectively), cumulative doses strongly depended on the length of stay as almost one radiograph per day is taken.
On average, the length of stay in the intensive care unit was 7 days; some cases with complications being hospitalized for several months, thus resulting in a maximum cumulative effective dose of 2.7 mGy.
Finally, the complementary information made available by the central computerized file at the radiology department level allowed us to take into account the contribution of the additional examinations to the total individual dose.
This work constitutes a preliminary step in assessing the feasibility and relevance of an epidemiological study dealing with the premature babies population. On the basis of the results gathered from the study, the importance of the optimization of the radiographic techniques used and radiation protection considerations applicable to this particular population will be discussed.