Evaluation de l’influence de la position et de l’orientation du dosimètre porté au niveau du col en radiologie et cardiologie et cardiologie interventionnelles

In practice and in recommendations, it is advised to use a dosemeter that is worn on the lead collar to estimate the eye lens dose. Even though the correlation between a dosemeter on the lead collar and the doses near the eye lens is not always very good, still this solution is seen as a pragmatic best possible solution. However, there are several severe problems with collar dosimetry that have not been investigated a lot. First, the dosemeter on the collar is calibrated in Hp(10), while it should measure Hp(3) for the eye lens. Secondly, by wearing on the lead collar instead of on the head, this will change significantly the backscatter response. Thirdly, and most important, the orientation and position of the collar dosemeter can vary significantly from one person to another. This will seriously affect the correlation with the eye lens doses. Especially in interventional radiology, the specific angular distribution of the radiation field compared to the position of the doctor, will make that the position of the collar dosemeter will have a big influence. A series of irradiation tests were performed to quantify the effect of the position of different body dosemeters and their correlation with the eye lens dosemeter. First, dosemeters were characterized in laboratory conditions. The dosemeters were positioned on a calibration phantom (both slab and cylindrical ones were tested) covered or not with a lead apron, and were irradiated in different set-ups (beam quality and angle). Secondly, the correlation between the body dosemeters and the eye lens dosemeters was investigated in hospital conditions using a Rando Alderson phantom and an angiographic system. Thirdly, measurements were performed on physicians during real interventional procedures. For the settings tested (beam projection and phantom orientation), the dosemeter positioned on the left side of the Rando Alderson's collar correlated better with the eye lens dosemeter. However, the ratio between the measured dose showed important variability. In those conditions, the collar dosemeter can only be used to give a raw estimate of the eye lens dose, and does not seem suited for replacing eye lens monitoring with a dedicated dosemeter. The preliminary results of the measurements on physicians showed important variability among the participants, and more measurements are currently performed.