A COMPARISON OF PATIENT DOSE FOR EXAMINATIONS OF THE UPPER GASTROINTESTINAL-TRACT AT 11 CONVENTIONAL AND DIGITAL X-RAY UNITS IN THE NETHERLANDS

The objective of this study was to derive the effective dose to patien ts from examinations of the upper gastrointestinal (GI) tract at 11 X- ray units in 10 Dutch hospitals. Entrance dose and entrance dose rate were measured at the surface of a homogeneous PMMA phantom and at the entrance surface of the image intensifier. Dose-area products (DAPs) w ere assessed during examinations of patients. The patients (334 female s and 256 males) ages were 18-95 years (average 52 years). Effective d ose was assessed from DAP using Monte Carlo computer calculations for male and female mathematical anthropomorphic phantoms. The DAPs measur ed during the survey showed substantial variations, i.e. an overall av erage value of 21 Gy cm(2) and a range of average DAP per X-ray unit v arying from 7 to 56 Gy cm(2). Variations in the number of images (8-28 ) and the fluoroscopy time (1.7 min-7.0 min) were also large. A DAP to effective dose conversion factor of 0.32 mSv Gy cm(-2) was derived fo r upper GI studies. The dose survey yielded an overall average effecti ve dose of 6.7 mSv. At one location an examination involving as many a s 28 projections was performed, whilst maintaining a DAP well below 15 Gy cm(2) and an effective dose below 6 mSv. This was achieved using m odern equipment (i.e. high frequency generator, digital spot films) wi th 0.2 mm additional copper filtration and a relatively high tube volt age. For examinations of the upper GI tract, the application of a refe rence value of 30 Gy cm(2) for the DAP will ensure that, in general, t he effective dose to individual patients will not exceed 15 mSv.