Dynamic wedge versus physical wedge: a Monte Carlo study.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Physical wedges (PW) are traditional tools used in radiotherapy to shape radiation beams.
• Dynamic wedges (DW) offer an alternative method for beam shaping, potentially altering radiation characteristics differently than PW.
• Understanding these differences is crucial for accurate dose delivery and treatment planning.

Purpose of the Study:

• To analyze the characteristics of dynamic wedges (DW).
• To compare the effects of DW versus physical wedges (PW) on beam spectra, energy fluence, angular distribution, electron contamination, and dose distributions.
• To provide data for dynamic wedge commissioning.

Main Methods:

• Utilized EGS4/BEAM Monte Carlo codes to simulate a 6 MV photon beam and calculate 3D dose distributions.
• Simulated DW using segmented treatment tables (STT).
• Validated Monte Carlo simulations by measuring percentage depth dose curves and beam profiles against experimental data (film, ionization chambers in water phantom).

Main Results:

• Monte Carlo simulations showed excellent agreement (within 2%) with experimental measurements.
• DW exhibited significantly less impact on beam spectral and angular distributions and electron contamination compared to PW.
• A 45-degree PW caused a 30% increase in mean photon energy (beam hardening) and a 5% dose reduction in the build-up region, effects not observed with DW.

Conclusions:

• Dynamic wedges (DW) have a less significant effect on photon beam spectra and electron contamination compared to physical wedges (PW).
• Significant dosimetric differences exist between DW and PW, impacting their clinical utility.
• The findings offer valuable data for the commissioning of dynamic wedges in radiotherapy.