Experimental verification of ion range calculation in a treatment planning system using a flat-panel detector

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Science

Background:

• Heavy ion-beam therapy offers high precision due to the Bragg curve's steep dose gradient.
• Accurate range calculation is critical for effective heavy ion therapy, as it directly impacts treatment outcomes.
• Previous research demonstrated ion radiography with amorphous silicon flat-panel detectors can accurately measure water equivalent thickness (WET).

Purpose of the Study:

• To evaluate the accuracy of WET calculations in treatment planning systems.
• To compare WET distributions measured by ion radiography with those calculated by treatment planning systems using patient-like phantoms.
• To assess the utility of ion radiography for identifying uncertainties in WET determination.

Main Methods:

• Developed an ion radiography technique using an amorphous silicon flat-panel detector.
• Measured the 2D WET distribution of an anthropomorphic phantom.
• Compared measured WET maps with WET distributions calculated from X-ray CT images used in treatment planning systems.

Main Results:

• Measured and calculated WET maps showed good agreement in overall shape and 2D distribution (mean ratio 1.004, SD 0.022).
• Discrepancies were observed at high WET gradients, attributed to unaddressed Bragg-peak degradation in treatment planning.
• Excluding regions with significant Bragg-peak degradation improved agreement (mean ratio 1.000, SD 0.012).

Conclusions:

• Amorphous silicon flat-panel detector-based ion radiography is a valuable tool for precise WET measurements.
• This technique can detect uncertainties in WET determination within treatment planning processes.
• The findings support the use of this imaging technique for complex phantom cases and improving heavy ion therapy accuracy.