In-beam range determination using an OpenPET system for helium, carbon, oxygen, and neon ion beams

Area of Science:

• Medical Physics
• Nuclear Physics
• Radiotherapy

Background:

• Multi-ion therapy utilizes helium, carbon, oxygen, and neon ion beams to improve charged-particle therapy efficacy.
• Nuclear interactions of accelerated ions produce positron-emitting nuclei, which decay via annihilation photons.

Purpose of the Study:

• To investigate the accuracy of ion beam range determination using annihilation photons measured by an in-house online PET system (OpenPET).
• To compare the performance of different ion species (helium, carbon, oxygen, neon) for range determination.

Main Methods:

• Irradiation of a polymethyl methacrylate phantom with helium, carbon, oxygen, and neon ion beams.
• Measurement of annihilation photons using the OpenPET system.
• Simulation of ion beam transport and annihilation photon production using the Particle and Heavy Ion Transport code System (PHITS).
• Determination of beam range by comparing measured and simulated planar-integrated annihilation photon distributions (PIADs).
• Quantification of range determination accuracy using Fisher information.

Main Results:

• Good agreement between measured and simulated PIADs for carbon, oxygen, and neon ions; discrepancies noted for helium ions.
• Ion beam range determination achieved within 2 mm accuracy for all four ion species with measurement times exceeding 3 minutes.
• Neon ions provided the highest Fisher information (indicating best accuracy) for measurement times under 135 seconds.
• Oxygen ions offered the highest range determination accuracy for measurement times beyond 135 seconds.

Conclusions:

• OpenPET measurements enable accurate ion beam range determination (within 2 mm) for helium, carbon, oxygen, and neon ions in 180 seconds.
• Neon ions offer superior range determination accuracy within 135 seconds, while oxygen ions are more accurate for longer measurement durations.
• This technique holds promise for enhancing the precision and efficacy of multi-ion radiotherapy.