Medical radiation exposure in Japan is among the highest in the world [1]. One problem is that the public has little opportunity to receive information concerning the amount of radiation exposure they have been exposed to. Currently, CT scanning accounts for 62% of the amount of medical radiation exposure [2] and must be managed appropriately. One solution is to develop a method for measuring the actual dose of radiation a patient receives during CT examinations.

<<Purpose>>

    In this presentation, we would like to propose a novel method to measure the correct dose based on one dosimetric value measured during a CT examination. Since the incident direction of X-rays is random, it is necessary to perform analysis that takes into account the incident direction of X-rays as shown in Fig. 1.

Fig 1: A schematic drawing to explain the difficulty in measuring the exposure dose...

<<Difficulty (issues) and Novelty>>

    During helical scanning CT examinations, it is difficult to estimate the effective radiation dose from a measured point dose because the surface distribution varies depending on the X-ray incident direction [3,4] as shown in Fig. 2.

Fig 2: Examples of the published data showing that the exposure dose on the patient's...

    In current X-ray CT diagnosis, exposure dose is managed using physical quantities such as Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP) [5]. These physical quantities are values measured using a standard phantom, so they are suitable for evaluating differences in various CT equipment, but not suitable for evaluating the amount of exposure a patient receives as shown in Fig. 3.

Fig 3: Comparison of dose measurement methods between the conventional (left) and...

    The concept of our idea is to establish direct exposure dose measurement as presented in Fig. 4. In order to estimate the incident direction of X-rays, we analyzed the image noise (standard deviation: SD) component of the X-ray CT image. Furthermore, the dose distribution on the patient's surface was estimated by fitting the dose distribution, which was measured using a human-body phantom in advance, to the actual measured value,.

Fig 4: The concept of our novel idea to establish direct exposure dose measurement....