Computing proton dose to irregularly moving targets.

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-guided Therapy

Background:

• Four-dimensional computed tomography (4DCT) and deformable registration are limited for irregularly moving targets.
• Human respiration during treatment often deviates from idealized periodic signals with baseline shifts.
• Accurate dose calculation for moving targets is crucial for effective radiation therapy.

Purpose of the Study:

• To describe a novel method for computing proton dose delivered to irregularly moving targets.
• To utilize 1D or 3D respiratory waveforms captured during treatment delivery.
• To address limitations of current methods in handling non-periodic breathing motion.

Main Methods:

• Developed a dose calculation procedure using CT/4DCT images and real-time 1D/3D respiratory waveforms.
• Transformed dose volumes into a beam-specific radiological depth space.
• Translated and summed proton doses based on measured target motion trajectories, then transformed back to Cartesian space.

Main Results:

• The method was validated using a synthetic lung phantom and patient data.
• Motion-corrected dose calculations showed good agreement with planned doses (e.g., 95.7% gamma passing for 2cm sinusoidal motion).
• The algorithm demonstrated accuracy in reproducing dose for both simulated and patient breathing patterns.

Conclusions:

• A method for accurately calculating proton dose to irregularly moving targets from a single CT image was successfully demonstrated.
• This algorithm can be a valuable tool for assessing the dosimetric effects of breathing motion.
• Potential applications include studying baseline shifts before or during radiation treatment.