SU-E-T-471: Beam Properties of an In-Room Proton Therapy Accelerator

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Accelerator Technology

Background:

• Proton therapy offers precise radiation delivery.
• Gantry-mounted systems enhance treatment flexibility.
• Characterizing beam properties is crucial for accurate dosimetry.

Purpose of the Study:

• Quantify basic beam properties of the first gantry-mounted proton therapy accelerator.
• Evaluate beam characteristics delivered directly to the patient without intermediate bending magnets.

Main Methods:

• Utilized Monte Carlo simulations (MCNPX) for prototype beamlines of the Mevion S250TM system.
• Generated 576 profiles including open, half-beam-blocked, fluence, and Bragg peak depth-dose curves.
• Determined and compared beamline parameters like virtual SAD, effective source size, and Bortfeld's Bragg curve approximation parameters (R0, σ, ε).

Main Results:

• Beam parameters showed smooth trends across different configurations and proton ranges.
• Range variations within configurations had minimal impact on extracted parameters.
• Parameters were successfully fitted as a function of proton range.

Conclusions:

• The gantry-mounted system exhibits high similarity in beam properties across configurations compared to other proton therapy systems.
• Range straggling and beam divergence remain nearly constant due to the system's design.
• Simplified characterization is possible, potentially reducing the number of measurements needed for treatment planning systems.