Experimental validation of a kV source model and dose computation method for CBCT imaging in an anthropomorphic...

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Dosimetry

Background:

• Kilovoltage cone-beam computed tomography (CBCT) is widely used in radiotherapy, but accurate patient-specific dose estimation remains challenging.
• Existing methods using nominal weighted CT-dose index (CTDIw) may underestimate the actual absorbed dose delivered to patients.
• A validated kV X-ray source characterization model is crucial for precise dosimetry in CBCT procedures.

Purpose of the Study:

• To experimentally validate a kV X-ray source characterization model for estimating patient-specific absorbed dose in kV CBCT.
• To compare the model-derived absorbed doses with measurements in homogeneous and anthropomorphic phantoms.
• To evaluate the accuracy of the model against nominal CTDIw dose estimates.

Main Methods:

• Simulated Varian on-board imager (OBI) CBCT protocols using a kV X-ray point-source model and source characterization.
• Computed absorbed dose in phantoms using in-house kV dose computation software (kVDoseCalc).
• Compared computed doses with ionization chamber and thermoluminescent detector (TLD) measurements.

Main Results:

• Computed absorbed doses agreed with measurements in a homogeneous phantom within ≤2% local dose (2 mm DTA in high-gradient regions).
• In the anthropomorphic phantom, computed doses showed good agreement with TLD measurements (average % difference 2.4% ± 6.0% to 5.7% ± 10.3%).
• The model-derived doses were approximately twice as high as nominal CTDIw estimates, consistent with published data.

Conclusions:

• The kV X-ray source modeling and characterization method accurately assesses patient-specific absorbed dose in kV CBCT.
• The findings provide evidence that CTDIw assessments commonly underestimate the absorbed dose delivered to patients during CBCT.
• This validated model offers a reliable tool for improving radiation safety and treatment planning in CBCT.