Computed tomography scanningparameters and radiation doses inpaediatric patients at Muhimbilinational Hospital

Abstract

ABSTRACT Background Computed tomography (CT) examinations have been increasing since its evolution in 70’s. Although it provides good contrast resolution and rapid scanning, it leads to larger doses of ionizing radiation compared to conventional x-ray. Children have much risk from a given radiation dose than adults both because they are more radiosensitive and they have longer life time in which a radiation-induced cancer could develop. CT scanning parameters are the main determinants of radiation dose received by the child; therefore it is important to adjust them according to child’s age and body size. The aim of this study is to determine CT scanning parameters and radiation doses for pediatric patients according to age and body size at MNH. Broad objective To determine Computed Tomography scanning parameters and radiation doses in pediatric patients at Muhimbili National Hospital. Methodology This is a hospital based cross sectional study which was conducted at Radiology department, Muhimbili National Hospital from September 2017 to March 2018. Children referred for CT scan were included in the study following informed consent from the parents/guardians. Children underwent CT examination by using a Siemens Somatom Definition Flash, Frank furt, Germany model dual tube with 128 slice, 64 slices each tube .Structured questionnaires were used for recording patients' demographic data, clinical indication of CT, and scanning parameters. CT dose estimation was calculated from CT dose calculator computer software supplied by Imaging Performance and Assessment of CT scanners (ImPACT). Data analysis was done using the Statistical Package for Social Sciences (SPSS) version 20. Statistical Association was done by using cross tabulations. P value of < 0.05 was considered statistically significant.

Results The mean age of the study participants was 6.3years with a range of 0.01-15 years. Majority of children were males, and the majority of children were from age group of 1-5 years. Head trauma was the commonest indication with the majority patient aged 6-10years.Sixty four percent (112/174) of the CT examinations were of the head, twenty six percent (45/174) were of abdomen and ten percent (17/174) were of the chest. The tube potential and tube current for head examinations were higher than for the chest and abdominal examinations. The mean tube potential and tube current for the head were 115.4kVp and 209.45mA respectively with no evidence of adjustment based on body size and age of the patient. The mean tube potential and tube current for chest and abdomen were adjusted for paediatric body size and age with the mean value of 84.52 kVp and90.42kVp for the tube potential and 126.5mA and 91.25mA for tube current respectively. The doses for Head CT examinations were higher compared to the chest and abdomen, the mean CTDIvol(mGy) 11.78, DLP(mGy.cm) 231.42 andCTDIw (mGy) 16.6, but relatively lower than other international values. The calculated meanCTDIvol 11.8, 0.89, 1.79 and DLP 232.6, 36.5, 86.5 for head, chest and abdomen respectively were significantly lower than the values displayed on the console i.e. 36.7, 2.7, 2.6 CTDIvol and 731.7, 78.6, 114.8 DLPs. Conclusion Scanning parameters for head CT examinations are not adjusted for paediatric examinations. The use of large tube potential and tube current for head examinations has led to large doses for head examinations. The radiation dose mean values for CTDI vol, and DLP were significantly lower than those from other countries, however lowest doses have been reported to IAEA. We therefore still have the chance to further reduce our doses to the lower levels than these so as to reduce the level of radiation to our children.

Recommendations 1.The use of recommended scanning parameters for head CT examination such as low tube potential (kVp) and low tube current in paediatric imaging should be adhered. 2. Further CT dose reduction is needed despite the fact that our doses are lower compared to many other international values. This is because we need to minimize the radiation dose to children to as low as reasonably achievable. . 3. Further studies with larger sample size should be conducted all over the country involving different CT centers, using this study as a base line to develop Diagnostic reference levels for paediatric CT examinations.