Treatment head design for multileaf collimated high-energy electrons

Area of Science:

• Medical Physics
• Radiation Oncology
• Beam Delivery Systems

Background:

• Conventional treatment heads are primarily designed for photon beams.
• Electron beams offer unique depth modulation characteristics beneficial for certain cancer treatments.
• Integrating multileaf collimated electron beams into existing treatment workflows presents technical challenges.

Purpose of the Study:

• To modify a conventional linear accelerator treatment head for the dynamic delivery of multileaf collimated electron beams.
• To investigate methods for optimizing electron beam characteristics, such as penumbra and virtual source position, for clinical use.
• To assess the feasibility of using a computer-controlled multileaf collimator (MLC) for both photon and electron beam shaping.

Main Methods:

• Monte Carlo simulations using the BEAM software package were employed for investigation.
• Key physical parameters including beam penumbra and virtual/effective point source position were optimized.
• Modifications included replacing air with helium, adding a helium bag, adjusting scattering foil and monitor chamber positions, and MLC repositioning.

Main Results:

• The study successfully identified modifications enabling the use of multileaf collimated electron beams.
• Computer-controlled MLC allows for automatic and dynamic beam delivery for both electron and photon beams.
• Optimized designs demonstrated clinically useful beam characteristics down to at least 9 MeV.

Conclusions:

• Modifications to conventional treatment heads can facilitate the use of multileaf collimated electron beams.
• Dynamic delivery of mixed electron and photon beams is achievable, offering greater treatment flexibility.
• These advancements enhance the potential for utilizing the specific dosimetric properties of electron beams in radiotherapy.