| dc.description.abstract | Abstract: With the development of
technology, the use of CT extended beyond
the diagnostic purposes and made a room for
complex radiotherapy treatment planning.
As the traditional diagnostic CT scanners
have small bore-size (typically 65–70 cm)
and curved patient couch which is not
suitable for virtual simulation with
immobilised devices. Therefore wide-bore
CT scanners with increased bore size (80-
100 cm) were introduced for radiotherapy
treatment planning. These virtual simulation
CT scanners are further equipped with an
external patient positioning laser system, flat
patient couch and specialized visualization
software. Due to the unavailability of
traditional CT scanner, theses wide (or
large)-bore CT simulators are used for
routine diagnostic procedures. The main
purpose of this study was to compare the
patient doses delivered by a wide (LB) and a
small-bore (AQ1) CT scanners to ensure the
safe use of wide-bore simulator for
diagnostic purpose. A standard head CT
phantom (16 cm diameter and 15 cm length)
made out of Polymethyl methacrylate
(PMMA) was positioned at the iso-centre and
100 cm pencil ionizing chamber was
positioned at the centre and periphery of the
phantom. The phantom was scanned under
different combinations of tube voltages (80,
100, 120, 135 kVp) and tube currents
(100,150, 200, 300, 400 mA) and the Dose
Length Product (DLP) in cGy were measured
for each location of the ion chamber using an
electrometer. The pitch and scan lengths
(0.813, 15 cm) were kept constant for each
measurement. Our study confirmed that the
wide-bore is delivering considerably more
dose than observed in AQ1 for head CT with
the same exposure parameters. This
increasement is more pronounced in
exposures above 200 mA and 120 kVp.
Therefore, the use of wide-bore simulator for
routine diagnostic CT examinations is safer
for lower kVp and mA but not encouraged for
all the routine diagnostic purpose without
further study. | en_US |
