26.07.2006
Dental X-ray examinations may require the presence of assisting persons for calming the patients. Here, the question arises, to which dose these persons will be exposed. Within the scope of a BMU/BfS research project (StSch4434), the dose of persons assisting during dental X-ray examinations was measured.
Representative examination scenarios were determined by both conversations with experts and some observations and conversations in the clinic for oral and maxilofacial surgery of the Hanover Medical University (MHH).
The X-ray examinations in dentistry can be subdivided into 4 types:
- panoramic picture of the denture,
- intraoral single tooth picture,
- remote lateral X-ray image and
- the rather unusual digital volume tomography.
The adjusted tube voltages lie in the range between 60 kV and 110 kV.
The presence of persons assisting in radiological examinations may be required in the case of small children and disabled patients or patients suffering from dementia. If possible, the assisting persons will leave the X-ray room for the short moment of the radiography.
For the measurements at the MHH, electronic personal dosemeters (EPD Mk2, Thermo Fischer Scientific) were used. Calibration of the dosemeters and testing of their adequacy for measurements in the "pulsed" radiation fields was performed previously at PTB.
For reasons of radiation protection, protective clothing must always be worn in rooms in which ionizing radiation is used. During the measurements, the occurring dose values should, however, be determined without the screening influence of this clothing so that the maximally occurring dose is also determined for a case when no protective clothing is worn. For this purpose, the dosemeters were fixed above the lead apron of the assisting persons.
Due to the fact that there are only a few assisting persons and that unnecessary irradiations must be avoided, the dosemeters had - for the majority of the measurements - to be placed at representative places in the X-ray room, as can be seen in the figure.
The figure shows a typical panoramic shot. The patient sits on a chair while the X-ray device is moving around her. The assisting person would sit besides the patient, on a chair outside the travel range of the X-ray facility.
Depending on the type of examination, the dose values measured (for assisting persons) lie in the range from 0.1 µSv to 4 µSv. This is comparable to the daily dose by natural environmental radiation of approx. 2 µSv.
To evaluate the risk for assisting persons, it must additionally be taken into account that the wearing of protective clothing can reduce the occurring dose values by up to a factor of 100, depending on the type of the protective clothing.
Figure : The assisting person would sit on the chair on the left in the picture. Accordingly, the electronic dosemeters (EPD Mk 2) for the measurements would be positioned there. Both patients and assisting persons wear protective clothing.