Range shift verification in spot scanning proton therapy using gamma electron vertex imaging.

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Instrumentation

Background:

• Proton therapy utilizes the Bragg peak for dose conformity, but beam range uncertainty significantly impacts treatment quality and patient safety.
• Managing range uncertainty is crucial for effective proton therapy.
• Prompt gamma imaging (PGI) is a promising technique for range verification in proton therapy.

Purpose of the Study:

• To report the first experimental results of the upgraded gamma electron vertex imaging (GEVI) system for prompt gamma imaging (PGI) in pencil-beam scanning (PBS) proton therapy.
• To evaluate the GEVI system's capability in measuring proton beam range shifts.
• To assess the accuracy and precision of the GEVI system for in vivo range verification.

Main Methods:

• Utilized homogeneous slab and anthropomorphic phantoms with defined planning target volumes (PTVs).
• Introduced various range shift scenarios and synchronized prompt gamma (PG) measurements with beam irradiation.
• Estimated range shifts by analyzing the centroid changes in aggregated PG distributions, employing range shift mapping, confidence interval estimation, and statistical hypothesis testing.

Main Results:

• Range shift mapping demonstrated a clear tendency aligning with true shift values, despite minor fluctuations in low-statistic spots.
• The GEVI system achieved overall accuracy and precision of 0.36 mm and 0.20 mm, respectively.
• Statistical tests confirmed the system's ability to detect shifts as small as 1 mm and discriminate between different shift magnitudes.

Conclusions:

• The GEVI system is feasible for measuring range shifts in spot scanning proton therapy.
• Experimental results validate the system's high accuracy and precision for detecting up to 1 mm of range shift.
• The GEVI system shows significant promise as a PGI system for in vivo range verification in proton therapy.