# Impact of Patient Size and Positioning on Radiation Dose in Multiphase Liver CT Examinations
## 1 Introduction  
Computed tomography (CT) examination of the liver is used, among other diagnostic methods, to evaluate primary tumors or cancer metastases within this organ. It also helps identify, localize, and characterize cancerous lesions. CT also allows for the detection of liver pathologies such as cirrhosis, cysts, steatosis, or inflammatory lesions. After cancer treatment, during oncologic therapy, or over the course of other liver diseases, this examination makes it possible to monitor the progress of therapy and evaluate possible changes in the organ [1]. According to the data collected by the National Health Fund inPoland, 877 patients underwent liver imaging by CT scan in 2022 [2]. Statistics collected from various countries around the world as of 2021 state that the number of all CT scans performed averages 156.6 per 1000 people. The same study reports that in Poland there are 116.5 examinations per 1000 residents [3]. Given the frequency of CT scans, it is important to consider the factors affecting the safety of this examination, with particular attention to the possible effects of ionizing radiation on the human body. The dose of ionizing radiation used in performing imaging examinations can range from a few to tens of millisieverts (mSv). Many factors influence this parameter, including the examination protocol and equipment used. The patient's body structure is also important, as different tissues absorb radiation differently [4]. The examinee is subjected to a different dose of radiation depending on the area of the body that requires imaging by radiation. The dose reduction techniques used, such as modern imaging technologies, optimization programs, as well as precise device settings, can significantly affect the radiation dose during the examination. The duration of the examination and the number of runs are also important [5]. Radiation dose management is a key aspect of medical diagnostics. Physicians, radiologists, and electrocardiologists strive to adjust the parameters of the examination in such a way as to obtain the necessary diagnostic information with minimal exposure of the patient to ionizing radiation. The constant development of diagnostic technologies and procedures is aimed at continuous improvement and minimization of radiation dose, while keeping high diagnostic quality [6]. Although the radiation dose per individual examination has decreased over time due to advancements in imaging technology, optimized protocols, and increased awareness of radiation safety, the overall collective dose to the population continues to rise. This increase is largely driven by the growing number of imaging procedures being performed overall [7; 8; 9]. Currently, thanks to years of research, the harmful effects of even low doses of ionizing radiation on health have been demonstrated, which raise concerns about its potential health risks [10; 11]. Ionizing radiation significantly increases cancer risk by inducing mutations in somatic cells. It can also impair the immune system, resulting in greater susceptibility to infections and other diseases. Therefore, it is important to minimize radiation exposure and adhere to reference dose levels tailored to specific examinations [12; 13]. Researchers also emphasize the importance of personalized dose control, especially for vulnerable populations such as pediatric patients or individuals requiring frequent imaging follow-up [14; 15]. In routine clinical practice, subtle misalignments in patient positioning--particularly shifts of the isocenter by just a few centimeters--often go unnoticed. When combined with an excessively large field of view (FOV), such positioning errors may result in unnecessary radiation exposure, even in patients with average body habitus. These factors, which are not accounted for by standard indices such as BMI, may significantly influence radiation dose metrics, including CTDIvol and DLP.