Technical Note: Experimental carbon ion range verification in inhomogeneous phantoms using prompt gammas

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Carbon ion therapy offers precise dose delivery but requires accurate monitoring of the ion range.
• Tumor motion or changes in tissue density can lead to significant variations in the carbon ion's stopping range.
• Prompt-gamma (PG) emission presents a promising real-time, non-invasive method for range verification.

Purpose of the Study:

• To experimentally validate the use of prompt-gamma (PG) emission for monitoring carbon ion range variations in inhomogeneous phantoms.
• To assess the feasibility of PG monitoring for detecting shifts caused by tumor movement or anatomical changes in carbon ion therapy.

Main Methods:

• Irradiation of inhomogeneous phantoms (mimicking bone/lung tissue) with a 95 MeV/u carbon ion beam.
• Acquisition of PG profiles using a slit-collimator setup and time-of-flight (TOF) for event selection.
• Definition and analysis of the prompt-gamma profile length (PGPL) to correlate with ion range shifts.

Main Results:

• PGPL shifts accurately reflected ion range variations as small as 1-2 mm.
• A -1.33 mm range shift resulted in a PGPL difference of approximately -1.9 mm.
• A +4.59 mm range shift led to a PGPL difference of approximately +4.2 mm.

Conclusions:

• Experimental data confirm PG emission's utility for monitoring carbon ion range in inhomogeneous environments.
• PG monitoring can detect clinically relevant ion range shifts of 1-2 mm.
• Optimized setups, informed by simulations, can achieve high accuracy (93%) in PGPL retrieval for therapy applications.