Control area around dental x-ray units - dosimetric study I

The issue of prompt professional occupational dose reporting is raised when the interval between doses is short or when the radiation source suffers a technical failure. Every involved person should be able to recognised individual or group radiation exposure. Actual radiation quality of the source is to be taken into account. To optimise radiation protection of dental radiologists, dental x-ray units were subject to Quality Control measurements. Scattering radiation from the patient's dental structures was measured in order to prove the results published by S. Tabakov, but using the modern RVG dental mode and several classical diagnostic positions. We used a special head phantom (real scull + Perspex + crown glass) and common dental x-ray units of various brands and types. The radiation quality was measured using standard QA/QC equipment. We measured the radiation scattered from the phantom in the horizontal plane (at thyroid height) at 0.5 m distance from the centre of the phantom. The measurement were done for a number of standard dental x-ray procedures, but this paper presents only the scattering caused by the upper premolars. The attenuation in the facial tissue was minimal and the majority of incidental radiation passes through the open mouth of a patient directly into the room area causing occupational exposure. The results we obtained are consistent with earlier reports on patient dosimetry. Occupational exposure is much lower if a modern RVG technique is used and no radiation protection threshold is exceeded in relation to Croatian laws. Much more important is the fact that the need for protective equipment and shielding is smaller if QA warrants proper technical operation of the x-ray tube. The maintenance of dental units is essential and so is a proper training of staff using modern diagnostic techniques. The control area around the x-ray unit is to be calculated and established for every standard dental unit (this does not apply for panoramic x-rays). To conclude, there is no need for overprotective measurements if a dental unit works in RVG mode, and the distance of 0.5-1 m from the rear of the x-ray tube head is sufficiently safe for a dentist or technician, assuming that they are using adequate personal protection. Real time scattered radiation exposure dose rate pattern proves that any worker or other employee working near a standard RVG x-ray unit mounted on the dental chair is not required by law to undergo any occupational monitoring (dosimetry or health). The total annual dose per person will probably not exceed 1 mSv under the worst working conditions. Hence, it is not necessary to provide legally required, or even additional, occupational health care programme.(author)