Factors influencing the absorbed dose in intraoral radiography

Abstract

The aim of the present study was to find out whether it was more effective to achieve a dose reduction in intraoral radiography with an increase in the tube potential setting (and a decrease of milliampere seconds) by an additional attenuation of the X-ray beam behind the film plane or by the use of digital radiography. A second aim was to find out if there were differences between the integral doses determined by two different detectors and two different phantoms. The X-ray attenuation in this in vitro study was carried out using additional lead foils from the dental film packet fixed behind the film plane and with a metal film holder. The dose measurements were performed with two semiconductor detectors (Quart, Diados). Patient simulation was achieved by the Alderson phantom or by the use of a filter (6Al+0.8Cu). The absorbed doses were calculated by integrating an exponential function between the entrance dose and the body exit dose. In addition, organ doses were measured and the effective dose was determined according to the Implementation of the 1990 Recommendations of the ICRP (ICRP-60). The increase in tube potential levels did not provide a substantial reduction of the absorbed dose (90 kVp instead of 60 kVp: reduction to 92.4%), only a reduction of the entrance dose (by 30% to 35% at 90 kVp compared with 60 kVp). The use of three lead foils behind the film plane instead of one resulted in a 14.0% reduction of the absorbed dose (60 kVp); the use of a metal film holder resulted in a 27.8% reduction (60 kVp). When tube potential settings were increased, the dose reduction decreased. The absorbed dose was reduced to 52% when a storage phosphor plate was used instead of a film (60 kVp). It was possible to determine the amount of dose reduction with both the calculated absorbed dose and the effective doses. The integral doses obtained from the Alderson phantom showed values 5% higher than those obtained by the filter (r(2)=96.7%). For the comparison of the integral doses, the measurements performed with Quart had values higher by a factor of 1.139 than those performed with Diados. Instead of increasing the tube voltage or using additional lead foils or metal film holders, a substantial dose reduction is provided by digital radiography or more sensitive films while a low tube potential level is maintained and the milliampere seconds setting is reduced.