Practical patient dosimetry for partial rotation cone beam CT

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Dosimetry

Background:

• Cone beam CT (CBCT) is widely used in medical imaging.
• Accurate estimation of radiation dose, particularly effective dose, is crucial for patient safety.
• Current methods for dose estimation in CBCT may require refinement.

Purpose of the Study:

• To investigate the validity of estimating effective dose for CBCT using weighted CT dose index (CTDIW) and irradiated length.
• To compare Monte Carlo simulations with direct measurements for dose assessment.
• To evaluate the impact of phantom length and projection number on dose calculations.

Main Methods:

• Measurements were performed using PMMA phantoms of varying lengths (14 cm and 28 cm) and diameter (32 cm).
• DynaCT acquisition was used on a Siemens Artis zee fluoroscopy unit.
• Organ and effective doses were estimated using the Monte Carlo software PCXMC.

Main Results:

• CTDIW closely approximated interpolated average dose when measured doses reflected X-ray beam rotation.
• Increasing phantom length from 14 to 28 cm increased average dose by 8%.
• Simplified PCXMC modeling (4 projections) yielded effective doses only 7% different from extensive modeling (41 projections), while organ doses varied up to 27%.

Conclusions:

• Effective dose estimation for CBCT using CTDIW and irradiated length is accurate with careful chamber positioning.
• A single CT dose index phantom may necessitate a conversion factor for dose estimation.
• Accurate estimation of organ doses necessitates a large number of modelled projections in PCXMC.