الفهرس 
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Abstract
Data from computed tomography (CT) is a crucial input in the radiotherapy treatment planning system (TPS), which incorporates the impact of inhomogeneities in dose calculations. Hounsfield unit (HU) measurement is influenced by scanning acquisition settings and scanner-specific characteristics. This study looked at how distinct kilo-voltage peaks (kVp) affected the HU for various tissue substitutes in two different phantoms and how their dosimetric effects affected dose computation in the Monaco TPS (version 5.11.02). from CT scans of the phantoms taken at various kVps, HU for various density materials was calculated. Radiation therapy plans were created using the Monaco TPS, and relative electron density (RED) calibration curves for two distinct phantoms were constructed. On both scan phantoms, thirty VMAT plans for varied situations were executed. For 6 MV, the impact of calibration curve fluctuation in TPS was determined. CatPhan phantom did not significantly change for HU of different density materials with varied kVp, while CIRS phantom showed a direct correlation between kVp and HU, with increases in kVp leading to a commensurate DROP in HU.
Breast tissue had the highest HU variation, with a maximum difference of 42.9% noted between HU values recorded at 80 kVp and 120 kVp. For tissues (adipose, breast, muscle, liver, and bone), HU is negatively correlated with kVp; the kVp value rises as HU falls. However, as the HU increases during lung inhalation and exhalation, the kVp value rises. The maximum densities of CatPhan and CIRS phantoms varied by ≥ 22% in HU values. For PTV, bladder, rectum, right femoral, and left femoral in prostate patients, the deviations were 4.2%, 3.2%, 3%, 3.8%, and 4%, respectively. The brain stem of patients with head and neck conditions showed the highest departure of 2.6%, whereas the heart of individuals with mediastinal conditions showed the highest deviation of 2.8%. In particular for high density material, it was discovered that CIRS was more practical for calibration than CatPhan phantom.
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