A completed audit cycle of the lateral scan projection radiograph in CT pulmonary angiography (CTPA); the impact on scan length and radiation dose

Aim To investigate the effect of incorporating a lateral scan projection radiograph (topogram) in addition to the standard frontal topogram on excess scan length in computed tomography pulmonary angiography (CTPA) and to quantify the impact on effective dose. Materials and methods Fifty consecutive patients referred for exclusion of pulmonary embolism who had undergone a CTPA examination with conventional frontal topogram to plan scan length (protocol A) were compared with 50 consecutive patients who had undergone a CTPA study with frontal and additional lateral topogram for planning (protocol B) in a retrospective audit. Optimal scan length was defined from lung apex to lung base. Mean excess scan length beyond these landmarks was determined. The mean organ doses to the thyroid, liver, and stomach, as well as mean effective dose, were estimated using standard conversion factors. Results The mean excess scan length was significantly lower in protocol B compared to the protocol A cohort (19.5 ± 17.4 mm [mean ± standard deviation] versus 39.1 ± 20.4 mm, p