Options for radiation dose optimisation in pelvic digital radiography: A phantom study

Purpose: To investigate the effects of phantom orientation and AEC chamber selection on radiation dose and image quality (IQ) for digital radiography (DR) examinations of the pelvis. Methods: A phantom study was conducted using a DR detector, utilising all AEC chamber combinations. Current recommended orientation (Cr-AEC) was with the outer AEC chambers cranially orientated. mAs (given), source-to-skin distance and kV _p data facilitated entrance surface dose and effective dose calculations. Six anatomical areas were blindly graded by two observers (3-point scale) for IQ. Statistical differences in radiation dose were determined using the paired Student's t-test. IQ data was analysed for inter-observer variability (ICC) and statistical differences (Wilcoxon test). Results: Switching phantom orientation (caudally orientated outer AEC chambers: Ca-AEC) reduced mean radiation dose by 36.8%, (p< 0.001). A minor reduction in median IQ (15.5 vs. 15) was seen (p< 0.001). One Ca-AEC orientated image (1.6%) had all anatomical areas graded 'inadequate' by at least one observer; all other images were considered 'adequate' for all areas. In the Ca-AEC orientation, at least a 44% dose reduction was achievable (p< 0.001) when only the outer AEC chambers were used. In the Cr-AEC orientation, at least 11% dose reduction was achieved (p< 0.001); here the central chamber was used alone, or in combination. IQ scores fell, but remained 'adequate'. Conclusion: Switching pelvic orientation relative to AEC chamber position can optimise radiation dose during pelvic radiography. AEC chamber position should be clearly marked on equipment to facilitate this. AEC selection should be an active process.