Akademik Veri Yönetim Sistemi
4TH INTERNATIONAL CONFERENCE ON LIFE AND ENGINEERING SCIENCES, İSTANBUL, TURKEY ICOLES 2021, İstanbul, Türkiye, 23 - 25 Eylül 2021, (Yayınlanmadı)
Computerized
treatment planning systems (TPSs) are used in external beam radiotherapy to
generate beam shapes and dose distributions with the intent to maximize radiation
doses to cancer cells while minimizing damage
to surrounding healthy. TPS provides dose information for
treatment plans using the electron density information obtained from computed
tomography (CT). CT numbers or Hounsfield Unit (HU) and uniformity are
important image quality parameters in quality control of CT systems. Therefore,
the consistency of the data obtained in reference values is important for the
reliability of dose accuracy.
CT
number from CT images provide information on the attenuation characteristics
of X- ray beam in a particular volume
element in patient body with respect to that of water at a specific kVp. It is
important to verify the effect of different CT scanning protocols on HU and its
effect on dose calculation. This study was carried out to analyse the effect of
different tube voltages (80-120 kVp) on HU for different materials in Catphan
600 phantom
and
their dosimetric impact on dose calculation in TPS. General Electric Discovery
Computed Tomography was used to acquire CT images from the phantom. Circular regions of interest (ROIs) were
defined on the CT images of the phantom within the sensitometric inserts, and
mean CT numbers for different materials (polystyrene, teflon, water, air) were
obtained. For this test, Ipem Report 91 state a remedial level of 10 HU for the
annual test and a suspension level of 30 HU for all tests frequencies relative
to baseline values. IEC do not state tolerance levels for measurement of CT
numbers from various materials. Measurements of all materials in this study were
within 30 HU from the average value and only teflon were outside 10 HU. Uniformity
was measured from upper, right, lower, left, and central regions in the
phantom. In this study, it showed that different kVp settings show no important
variation in the measured HU values. It was
observed that all measured values were compatible with the acceptance and limit
values in both systems and were within ± 30 tolerance values. But the highest
differencies was noted in case of high-density materials (teflon) and CT scan
at the lowest kVp. Therefore, it can be concluded that the clinical practice
with applying CT acquisition technique of 120 kVp is viable. The study also
evaluated the precision and uniformity of CT scans performed at different
times, and emphasized the importance of periodic quality control tests for
image quality and treatment accuracy.