Helium ion beam imaging for image guided ion radiotherapy

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Ion beam radiotherapy offers precise dose conformation but requires accurate patient alignment.
• Inter- and intrafractional variations pose challenges for internal geometry alignment during treatment.
• Developing sensitive imaging methods for ion beams is crucial for clinical translation.

Purpose of the Study:

• To develop a method for visualizing 1 mm thickness differences with 1 mm spatial resolution at clinically relevant doses.
• To address the need for precise internal patient geometry alignment in ion beam therapy.
• To evaluate the potential of ion radiography for enhanced treatment accuracy.

Main Methods:

• A dedicated ion radiography system prototype using Timepix semiconductor technology was designed and constructed.
• Helium ions were selected as imaging radiation due to reduced scattering and lower damaging potential.
• A data acquisition procedure and processing algorithm were established and evaluated using geometrical phantoms at the HIT facility.

Main Results:

• The developed method successfully avoided image degradation from secondary fragments through single ion identification.
• Image contrast-to-noise ratio (CNR) was increased by 350% and spatial resolution (SR) by 150% with data processing and track direction consideration.
• Helium radiographs demonstrated 50% higher SR than proton radiographs at comparable CNR, achieving a resolution of 0.1 g/cm² in water-equivalent thickness.

Conclusions:

• A specialized helium ion radiography method utilizing exclusively pixelated semiconductor detectors was successfully developed.
• The method demonstrated the achievement of clinically desirable image quality in simple phantoms at diagnostic dose levels.
• This advancement supports improved patient positioning and treatment accuracy in heavy ion therapy.