Low-dose CT allows for accurate proton therapy dose calculation and plan optimization.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiological Imaging

Background:

• Proton therapy offers precise dose delivery but is sensitive to anatomical changes during treatment.
• Daily CT scans are crucial for adaptive proton therapy but increase patient radiation dose.
• Reducing CT dose is desirable but may compromise image quality and accuracy.

Purpose of the Study:

• To investigate the impact of reduced CT imaging dose on proton therapy dose calculations and treatment plan optimization.
• To determine if lower signal-to-noise ratios in CT scans affect proton dose distribution estimation.
• To assess the feasibility of using low-dose CT for accurate proton therapy planning.

Main Methods:

• Developed and validated a simulation tool to create low-dose CT scans from standard-dose scans.
• Performed proton dose calculations and plan optimization using both standard-dose and simulated low-dose CTs.
• Evaluated water equivalent thickness (WET) calculations to assess noise accumulation with dose reduction.

Main Results:

• CT dose reduction up to 90% showed no significant effect on proton dose distributions, evaluated via dose-volume histograms and 3D Gamma analysis.
• Plan optimization results remained clinically equivalent between standard-dose and low-dose CTs.
• WET map similarity was maintained with less than 1% relative error even after a 90% CT dose reduction.

Conclusions:

• Low-dose CT imaging is a viable option for proton therapy dose estimation.
• Significant CT dose reduction is achievable without compromising the accuracy of proton therapy planning.
• This approach can reduce cumulative patient radiation dose in adaptive proton therapy settings.