Depth scaling of solid phantom for intensity modulated radiotherapy beams

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Water is the reference material for absorbed dose dosimetry protocols.
• Solid phantoms are used for absolute dose verification in intensity modulated radiotherapy (IMRT).
• Accurate absorbed dose measurement requires fluence and depth scaling factors, but spectral variations in IMRT beams complicate depth scaling.

Purpose of the Study:

• To investigate the effects of photon energy spectral variations on depth scaling factors for IMRT beams.
• To develop an accurate method for determining depth scaling factors in solid phantoms for IMRT.

Main Methods:

• Photon energy spectra variations were determined using EGS Monte Carlo simulations.
• Depth scaling factors for solid phantoms were calculated using effective mass attenuation coefficients and simulated spectra.

Main Results:

• The study clarified the impact of spectral variations on depth scaling.
• An accurate method for determining depth scaling factors for IMRT beams was produced.

Conclusions:

• Spectral variations significantly affect depth scaling in IMRT.
• The developed method improves the accuracy of absorbed dose measurements in solid phantoms for IMRT.