Proton range verification in homogeneous materials through acoustic measurements

Area of Science:

• Medical Physics
• Acoustics
• Radiation Oncology

Background:

• Clinical proton beam therapy requires precise quality assurance (QA) for accurate dose delivery.
• Measuring the Bragg peak (BP) depth is crucial for proton beam range verification.
• Current methods for BP depth measurement can be complex or costly.

Purpose of the Study:

• To evaluate protoacoustics as a simple and accurate method for measuring proton beam Bragg peak depth.
• To compare different signal analysis methods for protoacoustic measurements.
• To assess the feasibility of protoacoustics for clinical quality assurance in proton therapy.

Main Methods:

• Proton beam experiments were conducted using rectangular and cylindrical phantoms made of aluminum, lead, and polyethylene.
• Protoacoustic signals, generated by proton dose deposition, were measured.
• Four distinct methods were employed to analyze the protoacoustic signals and determine BP depth.
• Psuedospectral wave-equation simulations (k-Wave MATLAB toolbox) were used to model acoustic reflections.

Main Results:

• Method 4 demonstrated minimal error (<3 mm, uncertainty ≤1.5 mm) across all tested materials and geometries.
• Plastic phantoms yielded better accuracy than metallic ones with Methods 1 and 2 due to lower sound speed.
• Method 3, while not requiring material-specific sound speed characterization, resulted in the largest error.
• Simulations helped elucidate the origin of acoustic reflections within phantoms.

Conclusions:

• Protoacoustic measurements show promise as a low-cost, simple QA procedure for proton beam range verification.
• The accuracy of protoacoustics is dependent on the choice of phantom materials and signal analysis methods.
• Method 4 provides a highly accurate approach for BP depth determination using protoacoustics.
• Further implementation of protoacoustics could enhance efficiency and simplicity in clinical proton therapy QA.