INFLUENCE OF COMPUTED TOMOGRAPHY PARAMETERS ON THE RADIOTHERAPY PLAN CALCULATION
DOI:
https://doi.org/10.35120/kij5404603tKeywords:
Hounsfield unit, CT protocols, dose calculation, radiotherapy, SRS planAbstract
Contouring, planning and dose calculation in treatment planning systems (TPS) are based on computed
tomography (CT) images. Therefore, it is important to have developed, optimized and adapted scanning protocols
for specific anatomic regions and special radiotherapy modalities such as stereotactic radiosurgery (SRS). The aim
of this study was to determine influence of tube voltage, field of view size (FOV) and reconstruction kernels on CT
numbers and the resulting radiotherapy (RT) dose calculation.
This study was performed at Clinic of Oncology, Clinical Center University of Sarajevo. Verification electron
density and CT number values was performed using CIRS Thorax 002LFC phantom, while anthropomorphic CIRS
038 phantom for stereotactic end-to-end verification was used for the purpose of dose plan calculation analysis with
large bore CT simulator Canon Aquillion LB.The significant correlation between the tube voltage and the measured
values of CT numbers is significant for all materials (p < 0.05), except for water (p = 0.310). No significant
correlation between FOV and obtained values of CT numbers was found in any of the evaluated tissue equivalent
materials. Evaluating the impact of reconstruction kernels on Hounsfield units (HU), significant deviations were
found for the FC62, FC68 and FC07 reconstruction kernels. Also, analyzing the influence of reconstruction kernels
on the RT dose calculation, the extreme values are associated with Dmin/D in PTV for kernels FC41 and FC68, where
deviations from the values obtained using the baseline scanning parameters were -1.3% and -1.9%. For deviation of
1 HU in muscle tissue of CIRS 002LFC, the calculated Dmin/D in PTV of CIRS STEEV phantom will reduce by
0.79%. Similarly, the reduction of D₉₈ and D₂ would be 6.8 cGy and 3.03 cGy for 1 HU, respectively. Change of the
reconstruction kernels caused differences of 0.4% in Dmin/D calculation in clinical target volume (CTV).
CT scanning and reconstruction parameters may affect Hounsfield units, which could have an impact on dose
calculations in RT plan. Hence, it is recommended to standardize the scanning protocol used in calibration curve
generation for TPS. One should avoid use of different tube voltages and kernels, while according to this study, the
change of FOV will have no impact on dose calculations
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