Application of automatic vertical positioning software to reduce radiation exposure in multidetector row computed tomography of the chest

Objective: To determine the effect of automatic vertical positioning (AVP) software on radiation dose reduction in multidetector row computed tomography of the chest. Materials and Methods: Two hundred forty-three consecutive patients (mean age, 54; range, 20-93 years), who underwent 64-slice multidetector row computed tomography of the chest from November 2005 to April 2006, were included in this study. This study was approved by our institutional review board with waiver of informed consent. Technologists initially positioned the patient in the gantry by adjusting the table height (vertical positioning) using a laser guidance system and patient surface anatomy. AVP software was then used to determine the true vertical positioning of the patient based on matching the individual patient's mean centroid (center of mass) throughout the chest as determined by the lateral projection with the gantry isocenter and center of the bow-tie filter. The resultant reduction in surface radiation dose with this attenuation-based vertical positioning was then calculated. Software-determined changes in patient vertical positioning and resultant radiation dose savings were analyzed using the t test and Pearson correlation statistics. Results: Vertical positioning of the patients by the technologist differed from AVP with the bow-tie filter in 95.5% (232 of 243) of patients with an average vertical mispositioning distance of 33.2 +/- 1.1 mm (range, 5.1-97 mm). Among mispositioned patients, 97% (225 of 232) were vertically mispositioned below the isocenter with a mean distance of 33.8 +/- 1.1 turn (range, 5.1-97 mm) and 3% (7 of 232) patients were vertically mispositioned above the isocenter, with a mean distance of 12.7 +/- 2.8 mm (range, 6-28 mm). The average surface radiation dose reduction with AVP software was 19% +/- 1% (range, 1%-46.6%). There was a strong correlation between vertical mispositioning distance and the surface radiation dose reduction facilitated by AVP software (r(2) = 0.9, P < 0.001). Conclusion: AVP software can help in optimum patient vertical positioning leading to substantial reduction in surface radiation dose.