Electron wedges for radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Electron beams offer advantages over photon beams for radiation therapy due to their rapid dose fall-off.
• Conventional methods for shaping electron beams, such as physical wedges, are suboptimal and degrade beam quality.
• Intensity modulation presents a novel approach to shape electron beams without physical modifiers.

Purpose of the Study:

• To develop and evaluate intensity-modulated electron beams for creating wedged dose profiles.
• To enhance dose uniformity in brain tumor treatment using modulated electron beams.
• To reduce radiation dose to surrounding healthy tissues.

Main Methods:

• Intensity modulation of 10-50 MeV electron beams using a racetrack Microtron accelerator and a custom scan matrix.
• Generation of arbitrary dose profiles, including wedged distributions, by controlling pulse coordinates and intensities.
• Measurement of dose distributions in an anthropomorphic phantom using film and comparison with conventional techniques.

Main Results:

• Intensity modulation reduced the 50-90% penumbra by 40% and increased beam flatness by 80%.
• Wedged profiles were achievable at various angles up to 70 degrees, dependent on beam energy.
• Combined modulated electron beams resulted in smaller low-dose regions (20-70%) but larger high-dose regions (70-100%) compared to photon beams.

Conclusions:

• Intensity-modulated electron beams significantly improve dose distribution compared to photon beams for brain tumor radiotherapy.
• The technique provides sharper penumbra, better conformity to target volumes, and reduced margins.
• Normal tissue dose, specifically the 20-70% isodose region, was reduced by 30% using modulated electron beams.