214 Chapter 9 SF-12 questionnaires, we analysed differences in baseline characteristics between responders and non-responders. We express all effects on secondary outcomes as differences between groups with two-sided 95% confidence intervals. We hypothesized that replacing CXR by ULDCT would lead to a more efficient health care process, reflected in fewer admissions and a shorter hospital length of stay. We calculated the median hospital length of stay and the difference between groups in those admitted using the Hodges-Lehmann estimator. The effect on mortality within 28 days was expressed as an absolute risk difference. The effect on incidental findings is reported as the absolute difference in proportions of patients in follow-up. All analyses were performed in SPSS version 26. A standard deviation of 10 on the SF-12 was anticipated [22]. A power analysis showed that using a 0.05 significance level, 2400 participants were needed to achieve 80% power in excluding a 1 point lower mean SF-12 PCS score for ULDCT, using the two-sample t-test statistic, assuming no actual difference in the mean scores. This 1-point noninferiority margin comes down to a 0.1 effect size. Results Participants 4807 patients presented at the ED with suspected non-traumatic pulmonary disease (Figure 1). Of these, 2418 were included: 1208 were allocated to ULDCT and 1210 to CXR (Supplementary Table S1 for information on the total eligible group and Figure S1 for location and month of inclusion). Baseline characteristics of included patients were comparable between groups (Table 1). Presenting symptoms and clinical indication on the radiology request form were largely similar, although slightly more ULDCT patients presented with cough and fever and had bronchitis as possible diagnosis (Table 1). Eight ULDCT and seven CXR patients did not undergo the allocated imaging method. Another 92 patients (40 ULDCT, 52 CXR) only signed a short informed consent, retracted their informed consent during follow-up, or died within 28 days, leaving 1160 ULDCT patients and 1151 CXR patients available for analysis of the primary outcome (Figure 1). The results of ULDCT and CXR were directly communicated to the attending physician by phone. Clinical management was based on the initial report. In only 1.0% of ULDCTs and 0.6% of CXRs the initial report was adjusted by the supervisor, this was directly communicated with the attending physician. Information on the availability of prior imaging can be found in Supplementary text S2. The median ULDCT radiation dose was 0.2 mSv (interquartile range (IQR) 0.2 to 0.3 mSv). The median CXR dose was for portable anterior posterior (AP) CXR 0.02 mSv (IQR 0.02 to 0.03 mSv) and bucky CXR posterior anterior (PA) and lateral 0.05 mSv (IQR 0.03 to 0.07 mSv).
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