Evaluation of effectives doses to patients after whole body computed tomography

Abstract

Introduction Changes in technology of computed tomography (CT) have greatly improved this radiological examination. Image quality was improved, patient doses were lowered, meanwhile the duration of procedure greatly reduced. Use of automatic exposure control (current modulation systems) in CT helped reduction of patient doses. However, the constant change of tube current introduced difficulties when assessing patient dose. Usual dose descriptors, such as computed tomography dose index ( C vol ) or dose length product ( P KL , CT ) , represent average dose. This problem is emphasized in case when larger body volumes are examined, and especially in case of whole body CT that is most commonly used in combination with positron emission tomography (PET). The tube current is changing from very low values in head and neck region to the maximum values in shoulder area or pelvis. Average C vol could underestimate the dose in areas with more radiosensitive organs. Purpose The purpose of this study is to develop the methodology to use tube current modulation data for better estimation of patient effective dose. Materials and methods In order to address the issue we used the real patient tube current data to estimate the organ dose using available dosimetry calculators. All patients were subject to the whole body PET-CT examination. Code was developed to read DICOM data and perform all necessary calculations. Results Analysis of tube current data for 50 patients was performed. The data was used to estimate the effective dose and all organ doses. Conclusion The results obtained gave us possibility to more accurately assess the organ doses, and consequently the effective dose to patients. The analysis of tube current data allowed us to optimize patient protocols, making possible improvement of image quality or lowering the patient dose.