Monte Carlo study of MLC fields for cobalt therapy machine

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Modeling

Background:

• Automated Multi-Leaf Collimator (MLC) systems are crucial for precise radiation delivery in teletherapy.
• Existing cobalt-60 teletherapy machines in India can be enhanced with add-on MLC systems.
• Validation of new MLC designs is essential for ensuring treatment accuracy and patient safety.

Purpose of the Study:

• To computationally validate the design of an automated Multi-Leaf Collimator (MLC) for cobalt-60 teletherapy machines.
• To assess the accuracy of the MLC in defining radiation field sizes and dosimetric parameters.
• To compare Monte Carlo (MC) simulation results with treatment planning system (TPS) and measured data.

Main Methods:

• Monte Carlo (MC) modeling was employed to simulate the source and collimator geometry of the MLC system.
• The MLC's performance was evaluated for square fields (2x2 cm² to 14x14 cm²) and irregular fields.
• Percent Depth Dose (PDD) and profile data from MC simulations were compared with ROPS (Radiation Oncology Planning System) TPS and IMATRIXX measurements.

Main Results:

• The MC model accurately represented the MLC system, showing good agreement with TPS and measured data.
• The proto-I MLC demonstrated the ability to define radiation fields up to 14x14 cm² within 3 mm accuracy.
• Measured radiation leakage through leaf ends was 3.4%, and interleaf leakage was 7.3%.

Conclusions:

• The developed automated MLC system is validated for use with cobalt-60 teletherapy machines.
• MC modeling is a reliable tool for validating MLC designs and predicting dosimetric accuracy.
• The study supports the coincidence of optical and radiation fields, enhancing treatment planning precision.