SURFACE DOSE ESTIMATION BY A KAP METER FOR KILOVOLTAGE X-RAY BEAMS

Area of Science:

• Medical Physics
• Radiological Dosimetry
• X-ray Imaging

Background:

• Accurate entrance surface dose (ESD) estimation is crucial for patient safety in diagnostic radiology.
• Traditional methods for ESD measurement can be complex and require correction factors.
• Kilovoltage x-ray beams are widely used in various medical imaging procedures.

Purpose of the Study:

• To develop and validate a method for estimating the entrance surface dose (ESD) in a water phantom for kilovoltage x-ray beams.
• To utilize an air kerma area product (KAP) meter for direct ESD estimation.
• To compare the KAP meter's ESD measurements with established dosimetry techniques.

Main Methods:

• Calibrated a KAP meter using a plane-parallel ionization chamber and a 60Co absorbed dose-to-water calibration coefficient (${N}_{D,w}^{{}^{60}\mathrm{C}\mathrm{o}}$).
• Measured ESD in a water phantom using the calibrated KAP meter for various kilovoltage x-ray beam qualities and field sizes.
• Verified KAP meter measurements against ESD estimated using the air kerma calibration coefficient (NK).

Main Results:

• The KAP meter, calibrated with ${N}_{D,w}^{{}^{60}\mathrm{C}\mathrm{o}}$, provided ESD estimates comparable to traditional methods.
• The ratio of ESDs based on ${N}_{D,w}^{{}^{60}\mathrm{C}\mathrm{o}}$ and NK was 1.003, independent of beam quality.
• KAP meter measurements agreed within ±1.5% with plane-parallel chamber measurements across tested field sizes and source-surface distances.

Conclusions:

• A calibrated KAP meter allows for direct and accurate estimation of ESD in water phantoms for kilovoltage x-ray beams.
• This method eliminates the need for correction factors associated with conventional air kerma calibration.
• The findings support the use of KAP meters as a simplified and reliable tool for radiological dosimetry.