Dose reduction for CT in children with cystic fibrosis: is it feasible to reduce the number of images per scan?

Background: Reducing the dose for each CT scan is important for children with cystic fibrosis (CF). Objective: To determine whether the number of CT images and therefore the dose per CT scan could be reduced without any significant loss of information in children with CF. Materials and methods: A cohort of children with CF was followed with biennial surveillance CT scans, obtained in inspiration after a voluntary breath-hold as I-mm thick images at 10-mm intervals from lung apex to base. A random set of 20 baseline CT scans and 10 follow-up CT scans were blinded. Sets of every image (10-mm intervals), every second image (20-mm intervals), every third image (30-mm intervals) and a selection of three and five images were scored randomly using a published CT scoring system by one experienced observer. Results: The 20 subjects were 10 years of age with a range of 3.7-17.6 years at baseline. Fewer CT images resulted in a significantly lower (less abnormal) CT score and the number of patients positive for abnormalities decreased subsequently. At intervals greater than 20 mm no significant change in CT score over 2 years could be detected, while the CT scores at 10-mm (P=0.02) and 20-mm (P-0.02) intervals worsened significantly. Conclusions: A reduction in the number of inspiratory CT images by increasing the interval between images to greater than 10 mm is not a valid option for radiation dose reduction in children with CF.