1. Head computed tomography doses in four selected hospitals in Nigeria
Tom Adejoh (M.Sc)
*Mark C. Okeji (Ph.D)
**Musa Y. Dambele (M.Sc)
Radiology Department
NAU Teaching Hospital, Nnewi, Nigeria
*Department of Radiography & Radiological Sciences,
University of Nigeria
**Department of Medical Radiography
Bayero University, Kano, Nigeria
PACORI CONFERENCE, TANZANIA
FEBRUARY, 2017

2. BACKGROUND OF THE STUDY
Stochastic effects are main concerns of patient dose in CT (Ionnis, 2010).
Justification, limitations and optimization are relevant principles of CT radiation protection ( ICRP, 1996).
Efficient optimization → high quality images with minimal radiation dose (saravanakumar, 2014).
Regular dose audits will produce efficient optimization (Huda, 2008).
In Africa there is a paucity of literature on CT dose (Ogbole, 2014)

3. Global range for head CT
LITERATURE REVIEW CT
Dosimetrics
CTDIvol (mGy)
DLP (mGy-cm)
(Foley 2012; IEC 2002)
Global range for head CT
CTDIvol: 32 – 77 mGy
DLP: mGy-cm
(Saravanakumar, 2014; McCollough, 2009; Brix 2003)
LITERATURE REVIEW

4. STATEMENT OF THE PROBLEM
The region selected had the highest number of CT scanners of different models and radiation outputs.
A perusal of series ‘999’ showed consistent higher dose than the 1999 European Commission recommendations of 60 mGy (CTDIvol) and 1050 mGy.cm (DLP).
There was no evidence of dose survey since the scanners were installed.
To audit the CT dose from the subregion as a quality control measure
SIGNIFICANCE OF THE STUDY
Awareness on dose output for the CT community
Practical actions on dose optimization as a result of findings.
AIM OF THE STUDY

5. Method & MATERIAL
* Design: retrospective study
* Place of study: Three tertiary hospitals (centres A-C) & a private diagnostic centre in Anambra State of Nigeria
* Duration of study: February – August, 2016
*Ethical Considerations: approval & confidentiality settled
*Inclusion criteria
→for centre:highest throughput, available CT dosimetrics
→for subjects: ≥ 18 years, nil scalp pathology
* Scanners :GE, 4-slice; Toshiba, 16-slice (2x); Philips, 16-slice
* Data analysis: SPSS version 20.0

6. Methodology
A retrospective analyses of archived CT images of subjects aged ≥ 18 years
Confidentiality of digital information was maintained by the activation of image anonymity features on the console.
All the images that met the inclusion criteria were included in the study.
The exposure parameters extracted from the first axial series and the on-screen CTDIvol and DLP for the subjects were recorded.
The mean and 75th percentile of the CTDIvol and DLP were then calculated for each centre as well as for the four centres combined.
Data were subjected to descriptive statistics and analyzed using analysis of variance.

7. Table 1: Anthropotechnical parameters for head CT
RESULTS
Table 1: Anthropotechnical parameters for head CT
Variables
Range
Centre A
Centre B
Centre C
Centre D
M:F ratio
104:96
24:26
25:25
30:20
Age range
kVp
120
140 mA
220
250
mA modulation
Yes/No No
Yes
Gantry rot time (s) 1 2
Scan range (mm)
200
Pitch
0.75 – 1.5
1.5
0.7
0.75
Scan mode
Helical/axial
Axial
Helical
Azimuth
90/180
0/90

8. Table 2: DOSE OUTPUT FROM THE CENTRES
Variables
European Commission
75th percentile
Centre A B C D
All centres
Mean CTDIvol
(mGy) 60 58 57 73 44 55
75th percentile CTDIvol (mGy) 59 86 46 66
Mean
DLP (mGy)
1050
891
1195
1612
734
1108
75th percentile DLP (mGy-cm)
945
1414
1785
794
1444

9. Discussion Remedy Peer review Initial protocol Radiographer:
Programmer:
Initial protocol
Peer review
Radiographer:
Remedy

10. DISCUSSION CONTINUED
Initial programme: Default protocols that are faulty often give high radiation dose (centres B and C from table 1 & 2).
→ appropriate ab initio programme is a great step in dose optimization
Peer review of dose output places an obligation on radiographer to optimize: output from Nigeria were higher than recommended values by EC and from literature
Radiographer: The remedy for acceptable dose output lies with the radiographer’s regular dose audit.

11. RECOMMENDATIONS LIMITATIONS CONCLUSION
* Dose output from the four centres in Nigeria were higher (66 mGy/ 1444 mGy-cm) than the recommendations of the European Commission (60 mGy/ 1050 mGy-cm).
LIMITATIONS
Absence of dosimetrics on some scanners decreased our sample size
* A more widespread dose audit is advised
* Regular dose audit of CT scanners is recommeded
* Default protocol audit and remediation is also advised
* Radiologists should request for dose summary to place an obligation on CT radiographers to be dose conscious
RECOMMENDATIONS

12. REFERENCE
Foley SJ, McEntee MF and Rainford LA. Establishment of CT diagnostic reference levels in Ireland. British Journal of Radiology, 2012; 85(1018):1390– 1397
Ogbole GI, Obed R. Radiation doses in computed tomography: Need for optimization and application of dose reference levels in Nigeria. West African Journal of Radiology, 2014;21(1):1-6
Huda W, Nickoloff EL, Boone JM. Overview of patient dosimetry in diagnostic radiology in the USA for the past 50 years. Medical Physics,2008;35:5713–28.
International Electrotechnical Commission Medical electrical equipment—part 2–44: particular requirements for the safety of X-ray equipment for computed tomography. Geneva, Switzerland: IEC; 2002
McCollough CH, Primak AN, Braun N,Kofler J, Yu L, and Christner J, Strategies for Reducing Radiation Dose in CT. Radiological Clinics of North America, 2009; 47(1): 27–40.
Saravanakumar A, Vaideki K, Govindarajan KN, and Jayakumar S. Establishment of diagnostic reference levels in computed tomography for select procedures in Pudhuchery, India. Journal of Medical Physics, 2014;39(1): 50– 55.