Proton 3D dose measurement with a multi-layer strip ionization chamber (MLSIC) device

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Current quality assurance (QA) for intensity modulated proton therapy (IMPT) relies on 2D dose measurements at limited depths.
• Emerging techniques like FLASH radiotherapy require advanced QA tools capable of high spatiotemporal resolution 3D dose measurements.
• A need exists for a QA device that can accurately measure full 3D dose distributions for IMPT.

Purpose of the Study:

• To demonstrate the feasibility of using a dedicated multi-layer strip ionization chamber (MLSIC) device for 3D dose measurements in IMPT fields.
• To develop and validate a reconstruction algorithm for generating 3D dose distributions from MLSIC measurements.

Main Methods:

• Developed a MLSIC device with 66 layers of strip ionization chambers, capable of measuring 768 channels at 6 kfps over a 25 × 25 cm² field size.
• Implemented a reconstruction algorithm using a double-Gaussian-Cauchy-Lorentz model to reconstruct 3D dose distributions for individual proton spots and full beams.
• Evaluated the MLSIC performance using a clinical pencil beam scanning (PBS) plan, comparing measurements with simulations (Zebra, MatriXX).

Main Results:

• Successfully reconstructed 3D dose distributions for individual proton spots and summed them to obtain the full 3D dose distribution for the beam.
• 3D Gamma Index analysis showed acceptable agreement between MLSIC measurements and dose distributions from simulation tools.
• The MLSIC demonstrated its capability for spot-by-spot 3D dose measurement in PBS proton fields.

Conclusions:

• The developed MLSIC is the first pseudo-3D QA device capable of measuring 3D dose distributions for PBS proton fields on a spot-by-spot basis.
• This technology offers a significant advancement in QA for IMPT, supporting both current practices and novel techniques like FLASH radiotherapy.
• The MLSIC provides high-resolution 3D dose verification, enhancing the accuracy and reliability of proton therapy treatments.