Electron beam collimation with a photon MLC for standard electron treatments

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Standard electron treatments use patient-specific cut-outs for beam collimation.
• Advanced techniques like modulated electron radiotherapy (MERT) and mixed beam radiotherapy (MBBR) require more flexible collimation methods.

Purpose of the Study:

• To evaluate the dosimetric feasibility of using a photon multileaf collimator (pMLC) for electron beam collimation in standard radiotherapy treatments.
• To compare treatment plan quality and organ at risk (OAR) doses between pMLC-collimated and traditional cut-out-collimated electron beams.

Main Methods:

• A Monte Carlo model for pMLC-shaped electron beams was extended for extended source-to-surface distances (SSDs) and validated against measurements.
• pMLC-based and cut-out-based treatment plans were created for various clinical cases (breast boost, sternum, testis, parotid).
• Treatment plans were evaluated for target dose homogeneity and OAR mean doses.

Main Results:

• Monte Carlo simulations and measurements showed agreement within 3% of maximal dose or 2 mm distance to agreement.
• pMLC-based plans achieved comparable target dose homogeneity and OAR doses to cut-out-based plans.
• Slight increases in OAR mean dose were observed for pMLC plans in specific configurations (lateral OAR proximity, extended SSD with 6 MeV).

Conclusions:

• Photon multileaf collimators (pMLC) can effectively replace cut-outs for electron beam collimation in standard radiotherapy.
• Accurate dose distributions can be achieved with pMLC collimation, offering similar or improved treatment plan quality.
• This facilitates more efficient standard electron treatments and advanced techniques like MERT and MBRT.