Nigerian Journal of Basic and Clinical Sciences

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 16  |  Issue : 1  |  Page : 1--4

The estimation of effective radiation dose following computed tomography urography at Aminu Kano Teaching Hospital, Kano Nigeria


Idris Garba1, Aisha R Abdullahi1, Mansur A Yahuza2, Muhammad A Suwaid2, Yusuf Lawal2,  
1 Department of Medical Radiography, Bayero University, Kano, Nigeria
2 Department of Radiology, Bayero University, Kano, Nigeria

Correspondence Address:
Dr. Yusuf Lawal
Department of Radiology, Faculty of Clinical Sciences, Bayero University, Kano
Nigeria

Abstract

Background: Computed tomography urography (CTU) is an efficient radiological examination for the evaluation of urinary system disorders. However, the procedure exposes patients to a substantial amount of radiation dose associated with increased cancer risks. Objectives: To determine computed tomography (CT) dose index following CTU and to evaluate organs equivalent doses and cancer-induced risks. Materials and Method: A prospective cohort study was carried out at a tertiary health facility in Kano, Northwestern Nigeria. Ethical approval was sought and obtained. Patients Demographics scan parameters and CT radiation dose data were obtained from patients that had CTU procedure. Effective dose (ED), organ equivalent doses, and cancer risks were estimated using SPSS statistical software version 16 and CT dose calculator software. Results: A total of 56 consented patients were included in the study, consisting of 29 males and 27 females. Radiation dose data for CTU was estimated as follows: dose length product (2,320 mGy*cm), computed tomography dose index (9.67 mGy), and ED (34.5 mSv). The probability of cancer risks was also estimated to be 600 per a million CTU examinations. Conclusion: The study revealed that the radiation dose for CTU is considerably high with increase in cancer risks probability. Variations in ED between studies suggest that optimization is not fulfilled. Patient radiation dose estimate should be taken into consideration when imaging protocols are planned for CTU.



How to cite this article:
Garba I, Abdullahi AR, Yahuza MA, Suwaid MA, Lawal Y. The estimation of effective radiation dose following computed tomography urography at Aminu Kano Teaching Hospital, Kano Nigeria.Niger J Basic Clin Sci 2019;16:1-4


How to cite this URL:
Garba I, Abdullahi AR, Yahuza MA, Suwaid MA, Lawal Y. The estimation of effective radiation dose following computed tomography urography at Aminu Kano Teaching Hospital, Kano Nigeria. Niger J Basic Clin Sci [serial online] 2019 [cited 2019 Nov 19 ];16:1-4
Available from: http://www.njbcs.net/text.asp?2019/16/1/1/253403


Full Text



 Introduction



Computed tomography (CT) scan has witnessed dramatic improvement since after its invention.[1] The technique continues to increase and expand due to its high diagnostic yield. However, it is worthy to note that CT delivers radiation exposure at the higher end of the diagnostic range.[2],[3]

CT procedures represent a low percentage of the radiological examinations performed in imaging departments but account for a greater portion of the total collective effective dose arising from diagnostic imaging.[4]

Technological advancement has made it possible for CT to be considered as the gold standard in the evaluation of urinary tract abnormalities.[5] Several studies have shown that in addition to its high spatial and temporal resolution images, computed tomography urography (CTU) has proven superiority over conventional intravenous urography (IVU) and also plain KUB particularly in the diagnosis of urinary system disorders.[5]

CTU provides detailed information about the urinary system that is crucial for effective management of patients with urinary tract abnormalities. However, the procedure is associated with high-radiation exposure.[6] The radiation dose is even more alarming when a multiphasic technique is performed. The high-radiation exposure associated with CTU has been discussed in several studies.[7],[8] and the values reported fall within the documented causes of cancer incidence and radiation-induced malformations resulting from radiation exposure.[9] The possibility of cancer induction has been the major limitation in the expanding use of CT as an investigative tool in the field of medicine.

In our institution, CTU investigations are now becoming more frequent. The procedure is performed using five acquisition phases to cover the entire area of interest (Arterial to Excretory series). However, due to repeated exposure, there is a possibility of the patient receiving a radiation dose value that is much higher than the recommended diagnostic reference level.[7] Furthermore, since the area covered includes pelvic region, the dose to reproductive organs may be quiet significant.

This study, therefore, aimed at recording the radiation doses from CTU examinations and second, calculating effective radiation dose and cancer risks. The effective doses for CTU examinations can be assessed by obtaining the dose length product (DLP) and consideration of patient characteristics, multiplying this with the appropriate conversion factor. Following a routine CTU examination, the risk of cancer in a particular organ can be estimated.

 Materials and Method



A prospective cross-sectional study was conducted in the radiology department of an academic institution located in the Northwest region of Nigeria between May 2016 and October 2016. In total, 56 patients who consented to the study were included. Ethical clearance was sought and obtained from the research ethics board of our institution.

Patient-related parameters (weight, height, age, gender, and clinical history) and exposure-related parameters (tube voltage, tube current, scan length, and number of slices) were taken using a well-structured dose survey form. Radiation dose parameters, namely, computed tomography dose index (CTDI) and DLP were also recorded.

A multidetector Toshiba Aquillion-prime 160-slice scanner was used for the study. The CT scanner was manufactured in Otawara, Japan, 2008. It has a maximum KvP of 140, and a maximum tube current of 400 mAs with inherent filtration of 2.7Al equivalent.

The numbers of image series acquired for each patient were unenhanced, arterial, early venous, late venous, and excretory phases. All series of images were acquired from the xiphisternum to inferior border of the symphisis pubis.

The CT-DOSE software “Cal dose X” was used to estimate the organ absorbed doses and typical scanning parameters, such as gender, age, weight, height, kV, mAs, table increment, pitch, and slice thickness, of each scan were used as input data to the CTDOSE sheet in organ absorbed dose estimations.[9]

The equivalent dose was obtained as the product of the absorbed dose in tissue (mSv) and the radiation weighting factor WR. Since for X-rays, WR = 1, the organ absorbed dose here is numerically equal to the organ equivalent dose.

Effective dose (ED) was calculated using the formula: ED = DLP * k factor for abdomen which is 0.015.[10]

The risk of developing cancer in each irradiated organ following CTU procedure was estimated as the product of the mean organ equivalent dose and risk coefficients obtained from ICRP.[10] The overall lifetime for radiation-induced cancer probability was calculated using the CT dose software Cal dose X.[9]

 Results



In total, 56 patients were recruited for the study. The participants' age ranged from 12 to 77 years with mean and SD of 40.6 ± 16 years, respectively. The most common finding for CTU was a simple renal cyst (16%) and found commonly among young adults (15–44 years). Meanwhile, renal calculi (5%) and bladder mass (7%) were found mainly in pediatric age (114 years) and old adults (6580 years), respectively.

Descriptive statistics of the exposure parameters (kV, mAs, NS, and ST) and radiation dose parameters (CTDI and DLP) following CTU were highlighted in [Table 1] and [Table 2], respectively.{Table 1}{Table 2}

Patient organ(s) cancer risks were calculated from the organ equivalent dose and presented in [Table 3]. The organs with high-radiation dose were the spleen, stomach, ovaries, and uterus.{Table 3}

 Discussion



In this study, the mean ED from CTU was found to be 34.5 mSv per procedure. The result showed a marked difference and wide variations from what was obtained from previous studies.[5],[6],[9],[11],[12],[13] [Figure 1]. However, the CTUs in the present study were performed using a 160 slice MDCT scanner, which possess a better dose reduction capabilities than lower slice/detector CT scanners of older models; there was a statistically significant difference (P = 0.001) in terms of ED when compared with other studies performed on 4-slice MDCT scanners[4],[7] and 64-slice MDCT scanners.[5]{Figure 1}

The risk for radiation induced carcinogenic effects for CTU examination was estimated to be 6.0 × 10−4, i.e., 600-fold increased cancer induction risk per a million CTU procedures. The estimation was found to be about 42 times higher than that reported in a similar study,[5] which estimated the radiation risk to be 14-fold increased cancer risk per one million CTU examinations.

Organs which received relatively high doses were spleen, stomach, uterus, and ovaries, with spleen having the highest dose. The radiation dose received by patients undergoing CTU was substantial; thus, the radiation risk per procedure was observed to be high in this study.

The significant difference between the effective dose from previous studies and this study can be attributed to a number of factors, one of which is the differences in exposure parameters [tube voltages (kV), number of image series, and tube current-time product (mAs)]. Also, the difference in patient indication and software used to estimate the effective radiation doses may account for some variability in the dose estimates.[14] Furthermore, there may be justifiable reasons for some variability in practice of which the number of scan phases required for image interpretation and diagnosis is different among radiologists. CTU protocol used in our health facility includes five phases with same doses over the abdomino-pelvic region in each phase; several studies used a maximum of three to four phases and proper collimation to the area of interest per each series of the examination during the CTU procedure.[5],[6],[7]

Thus, the need for strict procedure protocol harmonization in order to improve CTU techniques preserves image quality and reduces unnecessary high-radiation exposures to patients. Also, the technical scan parameters used contributed significantly to the high-radiation dose received by patients in this study; hence, optimization of these scan parameters to reflect individual patient(s) specific diagnostic needs will significantly aid dose reduction.

 Conclusion



This study has established the mean effective radiation dose among patients undergoing CTU to be 34.5 mSv per procedure and an estimated cancer risk of 600 per a million CTU procedures. There was a significantly higher ED when compared with previous studies with the spleen bearing the largest brunt of the radiation exposures following a CTU imaging examination; hence, suggests the need for improved radiation dose optimization techniques among individuals undergoing Abdomino-pelvic CT scan procedures.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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