Fluence-modulated proton CT optimized with patient-specific dose and variance objectives for proton dose calculation

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Accurate relative stopping power maps are crucial for particle therapy planning.
• Proton computed tomography (pCT) provides these maps but can involve significant imaging dose.
• Fluence-modulated pCT (FMpCT) aims to reduce dose by concentrating protons in a region of interest (ROI).

Purpose of the Study:

• To develop and evaluate a novel optimization algorithm for FMpCT.
• To jointly optimize for reduced imaging dose and image variance objectives.
• To maintain image quality in the ROI for accurate treatment dose calculations while minimizing dose elsewhere, especially to organs-at-risk.

Main Methods:

• A new optimization algorithm was developed for FMpCT, calculating modulated imaging fluences.
• The algorithm considers joint objectives for imaging dose and image variance.
• Simulations were performed for three pediatric patients with head region tumors, using an initial uniform fluence scan or prior x-ray CT scan.

Main Results:

• The algorithm achieved target image variance within the ROI.
• Average imaging dose reduction outside the ROI was 74% (from 1.2 to 0.3 mGy).
• Re-calculated treatment doses on FMpCT images showed high agreement (above 98.3%) with uniform fluence pCT, and proton range evaluation met criteria.

Conclusions:

• Jointly optimized FMpCT images maintain the dosimetric accuracy of pCT.
• Significant dose reduction (by three quarters) is achievable outside the ROI.
• This method may allow for daily imaging in particle therapy, enhancing safety and accuracy.