2.5D imaging: obtaining depth information from 2D helium-beam radiographs

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Image Reconstruction

Background:

• Ion-beam radiography is a proposed daily on-couch imaging method for ion-beam radiotherapy range verification.
• Standard ion-beam radiographs provide only 2D projection data, lacking depth information crucial for anatomical change assessment.
• Extracting depth information from 2D radiographs is essential for precise radiotherapy delivery.

Purpose of the Study:

• To experimentally investigate a 2.5D imaging approach for extracting depth information from 2D helium-beam radiographs.
• To assess the accuracy and spatial resolution of the 2.5D imaging method in mimicking anatomical changes.

Main Methods:

• Acquired helium-beam radiographs of homogeneous and anthropomorphic phantoms at a therapy center.
• Mimicked anatomical changes by altering phantom geometry and acquiring data before and after changes.
• Reconstructed plane-of-interest difference images and analyzed spatial resolution using slanted edge and Tenengrad methods.

Main Results:

• Achieved depth accuracy below 11 mm for the plastic phantom using both analysis methods.
• Depth values for most gap positions in the plastic phantom coincided with ground truth within 2σ uncertainty.
• Attained a depth accuracy of 13⁺⁵_-7mm in the anthropomorphic phantom.

Conclusions:

• The 2.5D imaging approach experimentally demonstrated the ability to estimate anatomical change depth from 2D ion-beam radiographs.
• This technique is vital for determining if anatomical changes are within the treatment field, impacting treatment efficacy.
• 2.5D ion-beam radiography holds potential for daily on-couch imaging to enhance patient anatomy monitoring and radiotherapy precision.