Kilovoltage x-ray dosimetry--an experimental comparison between different dosimetry protocols

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Accurate kilovoltage dosimetry is crucial for effective radiotherapy.
• Several international protocols exist, including IAEA (TRS-277, TRS-398), DIN (6809), IPEMB, AAPM (TG-61), and NCS (report 10).
• Variations in these protocols can impact dose delivery accuracy.

Purpose of the Study:

• To experimentally compare the performance of major kilovoltage dosimetry protocols.
• To assess the agreement between protocols under clinical beam conditions.
• To evaluate the impact of using Monte Carlo-derived backscatter factors on protocol convergence.

Main Methods:

• Experimental comparison of IAEA, DIN, IPEMB, AAPM, and NCS protocols.
• Measurements performed in four clinical beams (30, 80, 120, 200 kV).
• Monte Carlo simulations used to derive backscatter factors for specific x-ray machines.

Main Results:

• General agreement within 1-2% for dosimetric data at the surface of a water phantom.
• IPEMB and AAPM TG-61 protocols showed ~7% lower absorbed dose than IAEA TRS-398 in a 120 kV beam using in-air calibration.
• Using Monte Carlo backscatter factors improved protocol convergence to within 4%.

Conclusions:

• Current kilovoltage dosimetry protocols demonstrate good overall agreement.
• Minor discrepancies exist, particularly with in-air calibration methods.
• Monte Carlo methods enhance the consistency of dosimetry protocols in the kilovoltage range.