A web-based computed tomography (CT) dose calculation system (WAZA-ARI) is being developed based on the modern techniques for the radiation transport simulation and for software implementation. Dose coefficients were calculated in a voxel-type Japanese adult male phantom (JM phantom), using the Particle and Heavy Ion Transport code System. In the Monte Carlo simulation, the phantom was irradiated with a 5-mm-thick, fan-shaped photon beam rotating in a plane normal to the body axis. The dose coefficients were integrated into the system, which runs as Java servlets within Apache Tomcat. Output of WAZA-ARI for GE LightSpeed 16 was compared with the dose values calculated similarly using MIRD and ICRP Adult Male phantoms. There are some differences due to the phantom configuration, demonstrating the significance of the dose calculation with appropriate phantoms. While the dose coefficients are currently available only for limited CT scanner models and scanning options, WAZA-ARI will be a useful tool in clinical practice when development is finalised.

A web system of WAZA-ARI is being developed to assess radiation dose to a patient in a computed tomography examination. WAZA-ARI uses one of organ dose data sets corresponding to the options selected by a user to describe examination conditions. The organ dose data have been derived by the Particle and Heavy Ion Transport code system, combined with Japanese male (JM) phantom. The configuration of JM phantom is adjusted to the averaged JM adult. In addition, a new phantom is introduced by removing arms from JM phantom to take into account for dose calculations in torso examinations. Some of the organ doses by JM phantom without arms are compared with results obtained by using a MIRD-type phantom, which was applied in some previous dosimetry systems.

A web-based dose computation system, WAZA-ARI, is being developed for patients undergoing X-ray CT examinations. The system is implemented in Java on a Linux server running Apache Tomcat. Users choose scanning options and input parameters via a web browser over the Internet. Dose coefficients, which were calculated in a Japanese adult male phantom (JM phantom) are called upon user request and are summed over the scan range specified by the user to estimate a normalised dose. Tissue doses are finally computed based on the radiographic exposure (mA s) and the pitch factor. While dose coefficients are currently available only for limited CT scanner models, the system has achieved a high degree of flexibility and scalability without the use of commercial software.

In 2007, a nationwide survey was conducted to determine the frequency of CT procedures in Japan in order to compare the current use of CT among developed countries. The frequency of adult and pediatric CT scans was estimated using a model based on the results of the survey. Survey questionnaires were sent to 2,266 CT facilities: 1,068 government hospitals and 1,198 other hospitals and non-hospital medical centers. The questionnaire requested information including the number of beds, outpatients per day, type of CT scanner, various body regions scanned, and the number of scans performed. The results of the study indicate that the number of CT procedures was closely correlated with the number of hospital beds. The authors estimate that approximately 20.5 million procedures were performed in 2005 and 21.2 million in 2006. The number of pediatric CT procedures was calculated by multiplying the total number of CT procedures by the estimated fraction of pediatric (0-15 y) CT procedures. Annual pediatric CT procedures were estimated to have been approximately 580,000 in 2005 and 600,000 in 2006. The present study indicates that the number of procedures per thousand of population, 166 for total CT and 32-34 for pediatric CT, is lower in Japan than in the U.S.

To clarify whether medical radiation exposure, especially from head computed tomography (CT), increases the risk of brain tumours in young patients in Japan, which ranks the second highest in the world in the number of paediatric CT examinations following the US. From 2011 to 2015, we performed a case–control study of 120 brain tumour patients and 360 appendicitis patients as controls. Reasons, the number of brain and head CT scans date were available from interviews. A cumulative radiation dose to the brain was calculated as a sum of doses received from head CT scans and from conventional x-rays and estimated using a reference table derived from a literature review of published studies. We performed conditional logistic regression to assess the risk of brain tumours from brain and head CT, and from conventional head x-ray procedures. The case group received on average 1.8 CTs to the brain area and 2.2 CTs to the whole head, with a mean estimated brain dose of 32 ± 13 mGy. The odds ratio for developing a brain tumour from having a brain CT was 0.93 (95% confidence interval: 0.38–1.82). This was hardly altered when adjusting for parental educational history and for other diseases (history of neurological disease and attention-deficit disorder/attention-deficit hyperactivity disorder). Neither whole head CT nor cumulative brain dose to the brain increased the risk of glioma or of all brain tumours. Although this study conducted in Japan, where ranks second in the number of CT scans conducted in the world, did not show an increased risk of brain tumours related to CT scans, it should be taken with caution due to a case–control study with limited sample size.