Evaluating the Generalizability and Effectiveness of the 10-to-10 rule

Background: Previous research has highlighted the benefits of reducing contrast media (CM), demonstrating positive impacts on patient safety, environmental sustainability, and health care costs. The 10-to-10 rule, introduced by a single-center study, adjusts CM dose to total body weight and tube voltage. This approach resulted in a reduced overall CM volume, with homogeneous attenuation and consistent diagnostic image quality (IQ) across varying tube voltages. Objectives: This study aimed to evaluate the effectiveness of the 10-to-10 rule in achieving consistent and homogeneous attenuation in vascular and parenchymal CT in a multicenter clinical practice setting across Europe. Materials and Methods: A total of 1,037 patients scheduled for CT of the coronary arteries (high-pitch and sequential CCTA), pulmonary arteries (CTPA), aorta (CTA aorta), and abdominal CT in portal venous phase or venous phase scans of the neck were included in this nonrandomized multicenter trial, conducted at 5 centers in the Netherlands, Germany, and Switzerland. Each center followed its standard scan and reconstruction protocol based on the clinical request. CM protocols were based on the 10-to-10 rule: A 10 kV reduction in tube voltage should be accompanied by a 10% decrease in iodine delivery rate for vascular studies or total iodine load in parenchymal studies, and vice versa. Objective image quality (IQ) was assessed by drawing region of interests, measuring attenuation [Hounsfield Unit (HU)], and calculating signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). In vascular studies, a reference line was included, representing the threshold for sufficient diagnostic IQ (CCTA—325 HU, CTPA—200 HU, and CTA Aorta—250 HU). 95% CI of the mean attenuation was calculated, and the lower bound of each 95% CI was used as the reference to assess whether attenuation met these thresholds. Generalized mixed models tested for significant differences in objective IQ across varying tube voltages, presented both unadjusted and multivariate adjusted by age and gender. Results: Results demonstrated no significant differences in attenuation for distal high-pitch CCTA, proximal sequential CCTA, distal CTPA, CTA aorta, abdominal portal venous phase scans, and the thyroid gland and sternocleidomastoid muscle in venous phase scans of the neck after adjusting for age and gender. Proximal high-pitch CCTA, distal sequential CCTA, and proximal CTPA yielded significant results ( P =0.030, P <0.001, and P =0.002, respectively). SNR and CNR showed no significant differences for all scan protocols. The majority of 95% CI lower bounds exceeded the predefined threshold for sufficient diagnostic IQ. Exceptions included high-pitch CCTA scans, where only the 90 kV level met the threshold, as well as in sequential CCTA at 120 kV, and CTPA at 110 and 120 kV, for which the lower bounds remained below the threshold. Conclusions: This study demonstrates the generalizability and effectiveness of the 10-to-10 rule in a multicenter trial setting and a large patient population, showing limited significant deviations in iodine attenuation across varying tube voltages for both vascular and parenchymal CT studies.