Assessment Of Detrimental Health Effect Of Radiation Associated With Diagnostic X-Ray Examinations At Four Centres In Nigeria

ABSTRACT

Radiation exposure during diagnostic X-ray examinations has been widely

reported as one of the sources of cancer induction. Information on X-ray machine and

exposure parameters are crucial to risk assessment, which in turn are important for

optimization of radiation protection measures. The documentation of radiation risk in

Nigeria is sparse and hence the effectiveness of radiation protection measures at

diagnostic centres has not been well established. This work was aimed at measuring

effective dose received by patients during diagnostic x-ray examinations and estimating

the associated risk.

Between the years 2004 and 2006, the beam output of x-ray machines at four

diagnostic centres with adequate regulatory activities were measured with non-invasive

x-ray meter. These centres include University College Hospital (UCH) Ibadan, Twotees

Diagnostic Centre (TDC) Ibadan, Obafemi Awolowo University Teaching Hospital

Complex (OAUTHC) Ile-Ife and National Hospital Abuja (NHA). Field sizes, focus to

skin distance (FSD), tube filtration, operating potential (kVp) and tube loading (mAs)

were measured and used to calculate Dose Area Product (DAP) per patient. Data on age

and examination type were recorded for 1034 patients which include 310(UCH),

276(TDC), 220(OAUTHC) and 228(NHA). These and calculated DAP were used to run

Monte Carlo program to obtain effective dose. The risk of cancer was thereafter

estimated using fatal cancer risk factor of 5 x 10-2 Sv-1. The results obtained were

compared with the risk estimates recommended by the International Commission on

Radiological Protection (ICRP).

UNIVERSITY OF IBADAN LIBRARY

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X-ray field sizes and FSD of the examinations considered ranged from 8 cm x 5

cm to 40 cm x 35 cm and 75 cm to 139 cm respectively. The tube filtrations (mmAl) at

UCH, TDC, OAUTHC and NHA were 1.7, 2.7, 1.7 and 1.0 +1.0 mmCu respectively

while the mean exposure parameters (kVp, mAs) were 69, 45; 76, 79; 100, 83; and 75, 28

respectively. Analysis of examination type showed that thoracic x-ray examination was

the most common (74.0%). This was followed by head and neck (11.0%), pelvic (8.0%),

lower limb (4.0%), abdomen (2.0%) and upper limb (1.0%). The mean age (years) of

patients was 38±1 at UCH, 32±1 at TDC, 27±1 at OAUTHC and 28±1 at NHA.

Examination procedures were the same in all centres except the use of anti-scatter grid

for thoracic examination at OAUTHC. In all x-ray examinations, DAP (mGycm2)

generally ranged from 70 to 38,155. The range of effective doses (mSv) at UCH, TDC,

OAUTHC and NHA were 0.01–0.11, 0.01–0.17, 0.24–4.74 and 0.01–0.10 respectively

while the corresponding estimated risks of cancer per million were 2–9, 2–22, 100–400

and 2-6. The values at OAUTHC were higher than ICRP risk estimates of 35 cancer cases

per million. This was traceable to selection of high kVp with high mAs and insufficient

tube filtration.

Radiation risks associated with diagnostic X-ray examinations were within

acceptable limit except at OAUTHC. For radiation risks to be within the recommended

limit, the use of high kVp with low mAs and careful application of anti-scatter grid are

encouraged.