Patient-specific quality assurance for proton depth dose distribution using a multi-layer ionization chamber in a...

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Proton therapy requires precise patient-specific quality assurance (QA) for accurate dose delivery.
• The single-ring wobbling method is used for proton beam delivery.
• Evaluating patient-specific QA for proton depth dose distributions is crucial.

Purpose of the Study:

• To investigate the utility of the Zebra multi-layer ionization chamber for patient-specific QA of proton depth dose distributions.
• To compare measurements from the Zebra chamber with treatment planning system (TPS) calculations and water phantom measurements.

Main Methods:

• Proton depth dose distributions were measured using the Zebra chamber and a motorized water phantom system.
• Calculations were performed using the XiO-M treatment planning system (TPS).
• Detector size corrections were applied to TPS data for comparison with Zebra measurements.

Main Results:

• Good agreement was observed between Zebra measurements and TPS calculations for simple compensator shapes.
• A 15% difference was noted for complex compensator shapes.
• Detector size-corrected depth dose distributions showed improved agreement within 3% in steep dose gradient regions.

Conclusions:

• The Zebra system is a valuable tool for rapid patient-specific QA of proton depth dose distributions in wobbled beams.
• Field size limitations exist for the Zebra system.
• Careful consideration of detector size effects is necessary for accurate comparisons in complex dose distributions.