Characterization of an extendable multi-leaf collimator for clinical electron beams

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Conventional electron applicators are limited for advanced conformal, modulated, and mixed beam therapy techniques.
• An extendable multi-leaf collimator (eMLC) presents a potential solution for more complex electron beam collimation.

Purpose of the Study:

• To investigate the feasibility and dosimetric characteristics of an extendable multi-leaf collimator (eMLC) for electron beam therapy.
• To compare the performance of the eMLC with standard electron applicators using Monte Carlo simulations and experimental measurements.

Main Methods:

• The extendable multi-leaf collimator (eMLC) was modeled using the EGSnrc Monte Carlo code.
• Simulations were validated against dose measurements on a Siemens Oncor linear accelerator across various energies (6-21 MeV) and source-to-collimator distances.
• Dose profiles, percentage depth dose curves, and treatment plans were analyzed and compared to standard electron applicators.

Main Results:

• Measurements and simulations showed agreement within 2%/2 mm for various air gaps.
• The eMLC exhibited a wider penumbra but reduced build-up dose (up to 4.2%) compared to standard applicators.
• The eMLC demonstrated effective bremsstrahlung leakage reduction and allowed for isocentric delivery, simplifying treatment setup.

Conclusions:

• The extendable multi-leaf collimator (eMLC) provides similar dose distributions to standard electron applicators while enabling more complex and efficient electron beam delivery.
• The eMLC facilitates faster treatments, potentially reduces dose to organs-at-risk, and eliminates the need for patient repositioning in isocentric techniques.
• Monte Carlo simulations are accurate for predicting eMLC performance and patient dose distributions.