On compensator design for photon beam intensity-modulated conformal therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Compensators are cost-effective for intensity-modulated radiation therapy (IMRT).
• IMRT compensator design aims to achieve an optimized primary fluence profile at the patient's surface.

Purpose of the Study:

• To discuss problems in IMRT compensator design, particularly beam perturbations.
• To derive a formula for optimal compensator thickness from primary fluence.
• To investigate the impact of cerrobend compensators on a 6 MV photon beam.

Main Methods:

• Utilized OMEGA Monte Carlo codes to simulate a 6 MV photon beam with cerrobend compensators.
• Derived a formula for optimal compensator thickness calculation.
• Analyzed changes in energy spectrum, mean energy, and percent depth dose.

Main Results:

• Compensators significantly alter the energy spectrum and mean energy of primary photons.
• Beam hardening's effect on percent depth dose is less significant than on the energy spectrum.
• Contaminant electron buildup dose and scattered photons from the compensator have negligible effects on surface dose and can be ignored in primary calculations.

Conclusions:

• Beam hardening effects can generally be disregarded in compensator design and dose calculations for IMRT.
• The influence of compensators on electron buildup dose is minimal and can be treated as a correction.
• Scattered photons from compensators do not affect surface dose, allowing calculations based solely on primary photons.