Conversion factor for CT dosimetry to assess patient dose using a 256-slice CT scanner.

Area of Science:

• Medical Physics
• Radiological Sciences
• Diagnostic Imaging Technology

Background:

• Modern CT scanners feature increased detector rows, rendering standard computed tomography dose index (CTDI) integration ranges insufficient for accurate dose measurement.
• Scattered radiation necessitates a 300 mm integration range for precise dose assessment with a 128 mm nominal beam width.
• The inconvenience of 300 mm phantoms for routine cone-beam CT patient dose checks requires an alternative solution.

Purpose of the Study:

• To develop a practical method for accurate patient dose assessment in advanced CT systems.
• To determine a conversion factor (CF) for adapting standard dosimetry measurements to new CT technology.
• To ensure reliable patient dose evaluation in clinical settings.

Main Methods:

• Calculated a conversion factor (CF) by dividing the weighted dose profile integral (DPI(w)) from a 300 mm CTDI phantom and ionization chamber by that from a standard 140 mm CTDI phantom and 100 mm chamber.
• Investigated the influence of nominal beam width and effective energy on CF values.
• Assessed the applicability of CF values across different CT systems.

Main Results:

• The conversion factor (CF) was determined to facilitate accurate dose measurements.
• CF values demonstrated an increase with rising nominal beam width and effective energy (range 1.5–2.0).
• The derived CF values are adaptable to other CT systems due to analogous dose profiles.

Conclusions:

• The developed conversion factor (CF) provides a practical solution for accurate patient dose assessment with advanced CT scanners.
• This method enables reliable dose evaluation in any hospital setting using standard dosimetry equipment.
• The findings support improved radiation safety protocols in diagnostic imaging.