article · Precision Radiation Oncology
Accurate dose calculation in radiotherapy treatment planning relies on calibrating computed tomography numbers, measured in Hounsfield units, to relative electron density. This research examined how changes in tube voltage affect these numbers across various tissue substitutes using two commercial phantoms, the CatPhan 503 and the CIRS 062 M. Scans were conducted at 80, 100, and 120 kilovoltage peaks, and the data was evaluated using 30 volumetric modulated arc therapy plans in the Monaco treatment planning system. The CatPhan phantom displayed no significant variation in Hounsfield units across varying voltages. Conversely, the CIRS phantom showed that increases in tube voltage led to decreases in Hounsfield units, with breast tissue displaying the greatest deviation. A disparity of at least 22 percent appeared between the highest-density materials of the two phantoms, leading to the conclusion that the CIRS phantom is more convenient for calibration.
Radiotherapy relies on precise computed tomography scans to target cancer tumours while sparing healthy tissue. Inaccurate density calibrations can compromise radiation dose calculations. By identifying how specific phantoms and machine voltage settings alter calibration numbers, medical physics teams can select better testing equipment and ensure radiation treatment plans calculate doses with greater accuracy.
This applied research directly informs medical physicists and radiotherapy departments selecting quality assurance phantoms for treatment planning systems. The findings provide guidance on equipment performance, showing that the CIRS 062 M phantom is preferable for calibration workflows. The work is applied and immediately relevant to clinical protocols, though the abstract does not indicate any newly developed hardware or commercial products for market deployment.
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Abstract Objective This study was carried out to analyze the effect of varying kilovoltage peak (kVp) on Hounsfield unit (HU) for various tissue substitutes in two different phantoms and their dosimetric impact on dose calculation in Monaco treatment planning system version 5.11.02. Methods HU for different density materials was obtained from computed tomography images of the phantoms acquired at various kVps (80, 100, and 120). Two different phantoms (CatPhan 503 and CIRS 062 M) were used to construct their suitability for computed tomography. Both scan phantoms were used to perform 30 volumetric modulated arc therapy plans. Results No significant variation in the CatPhan phantom was observed for HU of different density materials with various kVp. In contrast, a direct relationship between kVp and HU was observed in the case of CIRS phantom, as increases in the kVp resulted in a corresponding decrease in HU. The maximum HU deviation was found in breast tissue. HU is inversely proportional to the kVp for tissues. There was a difference of ≥22% in HU values between the highest densities in CatPhan and CIRS phantoms. Conclusion CIRS 062 M was found more convenient for calibration than CatPhan 503, especially for high‐density material.
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DOI: 10.1002/pro6.1177
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