| dc.description.abstract | Since the discovery of x-rays in 1895, and more recently the use of
computerized Tomography (CT) there has been a growing interest in
the assessment of the radiation energy absorbed by the patients
during CT and other diagnostic x-ray procedures.
Consequently, there has been a development of radiation detectors
for patient dose measurements. Among such devices is the (LiF)
Lithium Fluoride, Thermoluminescent Dose Meter (TLD), which is
placed on the skin surface of the patient being monitored. Some
of the desirable properties of TLDs are high sensitivity and near
energy -independence.
Tests have been conducted to assess the suitability of TLDs during -CT procedures, with positive results.
Between September, 1993 and February 1994, a total of 75 patients
who underwent CT-examinations of the head, at Kenyatta National
Hospital were studied. While they were scanned their radiation
doses were determined. The anatomical landmarks were chosen to
correspond to the organs under dose assessment.
Thermoluminescent. dosimeters (LiF) were placed on the site of
interest before commencement of the CT procedure. After the
procedure was completed, the TLDs were taken for readout using the
TOLEDO 654-TLD Reader.
The organs monitored were the frontal bone, eyes (lens), parotid,
submandibular and thyroid glands.
other peripherally located organs were also surveyed, but only for
a few patients, in order to establish how much stray radiation
reached them. These organs were sternum, ovaries and testes.
Of the 75 patients, (25.3%) were referred for trauma while (74.7%)
were non-trauma patients.
Adults represented 82.7% of the patients while only 17.3% were
children.
Among patients attended, 64.0% were male and 36.0% were female.
The number of slices per CT-examination of the head ranged from 13
to 52. The mean doses to the thyroid among adult patients recorded
to be O.28mGy while the testes and ovaries among adults were
O.06mGy and 0.07mGy respectively.
The difference of the radiation doses among
undergoing CT-examination of the head were
significant at P<0.05.
adult patients statistically
The current study shows that by scanning the head through the
orbit, the mean absorbed dose to the eyes is 1.48mGy and 1.19mGy
for scanning to avoid the orbits; four times less than those
reported in the studies done elsewhere. Infact scanning to avoid
the orbits was 5.58mGy. Scanning through the orbits in the same
study was reported to be 43.44mGy higher than figures obtained in
this study.
This study also reveals that post contrast mean doses recorded are
higher than pre-contrast doses. It agrees with the figures reported
in studies conducted under reference above.
An attempt to address the issue of gantry tilt versus absorbed
doses has been made, as angling the gantry cranially can contribute
to reduction in radiation dose to the lens of the orbit.
Among radiation detector devices, TLDs are highly recommended
during cT-scanning of the head because of their overall
sensitivity. They do not produce artifacts on radiographic image.
This study reveals that the absorbed doses to the eyes, frontal
bone and parotid glands are higher than the rest organs around the
Head.
During CT-scan of the Head, this series shows that organs around
the head receive low mean absorbed dose when the gantry is angled
cranially to avoid the eyes. Thus setting on angle the gantry
cranially to avoid the orbits during Head scanning can contribute
to the reduction of the radiation dose.
Further studies of patient radiation dose during CT-examination not
covered in this work are suggested.
A comparative study of patient radiation doses between different
CT-models available in Kenya ought to be undertaken in future | en |
| dc.description.department | a
Department of Psychiatry, University of Nairobi, ; bDepartment of Mental Health, School of Medicine,
Moi University, Eldoret, Kenya | |
