# Impact of Patient Size and Positioning on Radiation Dose in Multiphase Liver CT Examinations
## 2 Materials and Methods  
A retrospective analysis was conducted on studies performed between 1 March and 15 December 2023 at a university hospital in Poland. Data were collected from Guerbet's Dose&Care dose monitoring system.  
Based on the data received from the dose monitoring system, the following were determined:  
1. Whether the patient was in the isocenter--Figure 1 shows the patient outside the isocenter, while Figure 2 shows the patient inside the isocenter.  
2. Information about the scope of the examination performed (abdominal or abdominal with pelvis)
3. Number of phases performed for each test
4. Total DLP (DLP for the entire study) and DLP for the liver imaging phase  
Only studies for which 4 imaging phases were performed were used for analysis: native phase (phase before contrast administration), arterial phase, venous phase, and delay to the liver (standard at 3 min after contrast administration). Cases for which the patient's weight or height was not given were also excluded.  
Figure 1: Image from the Dose&Care system showing patient placement outside the isocenter.  
Figure 2: Image from the Dose&Care system showing patient placement in the isocenter.  
In addition, the widest point in the abdominal area was measured on the patient's toposcan in the Horos software (4.0.0 RC5). The measurement scheme is shown in Figure 3.  
1. Do BMI, weight, and patient height affect total DLP and DLP in the liver phase?
2. Does the patient's max dimension affect the total DLP and DLP in the liver phase?
3. Does the patient's max dimension correlate with BMI and weight?
4. Does the max. patient size affect the X-ray tube performance (kV, mA)?
5. Do the patient's BMI, weight, and height affect the X-ray tube's performance?
6. Does the isocenter affect the total DLP and DLP in the liver phase?
7. Does the isocenter affect the X-ray tube performance?  
For the analysis, studies performed using a three-phase liver protocol in 258 patients (including 135 women and 123 men) were used. Due to missing data in some cases, the number of patients included may vary across individual statistical analyses. All examinations were performed using a Siemens SOMATOM Definition Edge scanner. The study group consisted of 80 abdominal and 178 abdominal and pelvic examinations. In our study, the isocenter shift did not exceed 5 cm. Patients were classified as being \"in the isocenter\" if the patient's isocenter coincided with the scanner's isocenter; otherwise, they were assigned to the \"not in the isocenter\" group.  
Figure 3: Diagram for measuring the patient’s widest point based on the toposcan performed.  
Patient demographics are summarized in Table 1. Patients in the Abdomen-only cohort (_n_ = 80) had a mean height of 1.69 \(\pm\) 0.09 m, a mean weight of 80.4 \(\pm\) 14.1 kg, and a mean BMI of 28.0 \(\pm\) 4.2 kg m\({}^{-2}\). The Abdomen + Pelvis cohort (_n_ = 178) was similar in height (1.68 \(\pm\) 0.09 m) but lighter (73.8 \(\pm\) 13.9 kg) with a lower mean BMI of 26.3 \(\pm\) 4.3 kg m\({}^{-2}\). Median and inter-quartile ranges (IQR) are provided for completeness. A detailed breakdown of BMI categories is available in Table 2.