MO-A-213AB-08: 2D Water Equivalent Path Length Imaging Technique for Pre-Treatment Range Verification in Proton...

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Proton therapy requires precise range verification for optimal dose delivery.
• Real-time imaging of moving targets, such as tumors, is crucial for adaptive radiotherapy.
• Current methods for range verification may lack real-time capabilities or introduce significant dose.

Purpose of the Study:

• To evaluate a novel detector's capability in generating transmission images based on Water Equivalent Path Length (WEPL) values.
• To assess the detector's potential for real-time imaging of moving targets in proton therapy.
• To determine the feasibility of using dose rate measurements for WEPL derivation.

Main Methods:

• Utilized a flat-panel 2D detector array with high time resolution (2 ms).
• Measured dose rate as a function of time for passively scattered proton beams in various phantoms.
• Analyzed time-dependent dose rate data to derive WEPL values.
• Assessed real-time imaging by tracking a moving phantom simulating a mobile tumor.

Main Results:

• Achieved millimeter accuracy in WEPL determination in water tanks.
• Successfully reproduced geometrical shapes of simple phantoms (wedge, sphere).
• Observed slight WEPL reconstruction deterioration in complex phantoms due to scattering and range mixing.
• Demonstrated potential feasibility for tracking moving targets in the coronal plane.

Conclusions:

• The novel detector provides WEPL imaging with minimal patient dose (<1 cGy), suitable for pre-treatment 'range-tuning'.
• This technique allows for adjustment of proton range based on determined radiological path length compared to treatment planning.
• Facilitates adaptive proton therapy by enabling real-time verification and adjustment of the proton beam range.