Measurement of Single Scan Dose Profiles in CT Using a Commercial Photodiode

Computed tomography (CT) is a significant source of medical X-ray for the general population. As an alternative method to the 100 mm long ionization chamber, which is normally used to measure the CT dose index (CTDI), some studies use smaller semiconductor photodetectors to measure the single scan dose profile (SSDP). In this case, the CT dose profiles are obtained by scanning the device through the beam using multiple rotations of the X-ray source. Some advantages of using electronic devices as radiation detectors include their high sensitivity, small physical size, no need for high voltage, and the capability of real time measurements. In this study the SSDP was obtained by using a photodiode in two ways: a detector built with only one device, and an innovative detector based on a time-multiplexing signal from an array of 31 photodiodes. Moreover, since most clinical CT examinations involve multiple scans as the patient is translated through the gantry, the novel detector was also used to obtain the multiple scan average dose (MSAD). Unprecedented results provide details of the single slice dose profile and MSAD curves, showing that such an innovative detector would be an advance in CT dosimetry and quality assurance.