Toward adaptive proton therapy guided with a mobile helical CT scanner

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Image-guided adaptive proton therapy (IGAPT) requires high-quality imaging for accurate treatment delivery.
• Traditional CT scanners may limit the flexibility of adaptive radiotherapy workflows.

Purpose of the Study:

• To assess the feasibility of using a mobile helical CT (mCT) system for IGAPT.
• To evaluate the imaging performance and geometric accuracy of the mCT for proton therapy applications.

Main Methods:

• CT images acquired using a 32-slice mCT on a robotic couch.
• Geometric integrity, localization accuracy, and image quality evaluated per AAPM TG-66.
• Relative stopping power ratio (RSPR) accuracy assessed via water equivalent distance (WED) and dose calculations on phantoms.

Main Results:

• mCT images exhibited slightly lower spatial resolution but higher contrast-to-noise ratio than standard helical CT.
• Geometric accuracy was <1 mm, with localization accuracy <0.4 mm and <0.3°.
• WED discrepancies were negligible (0.8 ± 0.6 mm for brain, 1.3 ± 0.9 mm for lung).
• 3D gamma analysis (3%/3 mm) passing rate exceeded 95% for dose calculations on mCT compared to planning CT.

Conclusions:

• The mCT system demonstrates sufficient geometric integrity, image quality, and RSPR accuracy for IGAPT.
• This technology supports the implementation of adaptive proton therapy with enhanced precision.