Technical Note: A methodology for improved accuracy in stopping power estimation using MRI and CT.

Area of Science:

• Medical Physics
• Radiotherapy
• Biomedical Imaging

Background:

• Proton therapy offers physical advantages for cancer treatment by targeting tumors.
• Accurate proton range estimation is crucial but challenged by CT-based stopping power ratio (SPR) calculations.
• Differences in x-ray and proton interactions limit current CT-based methods.

Purpose of the Study:

• To develop and validate a novel multimodal imaging method for estimating SPR.
• To compare the new method's SPR estimations against physical measurements.
• To assess the accuracy of MRI-based SPR calculations versus the current clinical standard.

Main Methods:

• Calculated SPR using the Bethe-Bloch equation from relative electron density and mean ionization potential.
• Extracted parameters from Dixon MRI sequences (water-only, proton density-weighted) and CT (kVCT, MVCT).
• Compared multimodal imaging SPR to physical measurements and kVCT-based stoichiometric method.

Main Results:

• The multimodal imaging approach (MRI with kVCT or MVCT) closely agreed with physical SPR measurements.
• SPR values estimated using MRI and MVCT were within 1% of physical measurements.
• The novel method demonstrated higher accuracy than the stoichiometric method for tested tissues.

Conclusions:

• A practical multimodal imaging framework for improved SPR estimation was successfully developed.
• This method enhances the accuracy of proton range calculations in radiotherapy.
• The findings support the potential of MRI-based multimodal imaging for optimizing proton therapy.