A feasibility study for megavoltage cone beam CT using a commercial EPID

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Image Reconstruction

Background:

• Electronic Portal Imaging Devices (EPID) are commonly used in radiotherapy for dose verification.
• Cone-beam computed tomography (CBCT) offers volumetric imaging capabilities but often requires specialized hardware.
• Integrating standard EPIDs for tomographic reconstruction presents a cost-effective alternative.

Purpose of the Study:

• To evaluate the feasibility of using a commercial EPID and the Feldkamp algorithm for cone-beam tomographic reconstruction.
• To characterize the performance of the EPID-based system in terms of resolution and dose accuracy.
• To identify and address potential sources of image artifacts.

Main Methods:

• Utilized a standard commercial EPID attached to an isocentric linear accelerator.
• Employed the Feldkamp algorithm for cone-beam tomographic reconstruction.
• Implemented corrections for pixel value conversion to exit dose and realignment due to detector sag.
• Collected half-cone projections due to limited EPID size and applied corrections for detector sag.

Main Results:

• Achieved cone-beam tomographic reconstructions with a sensitive volume of radius 21 cm and length 17 cm at 1.5 geometric magnification.
• Demonstrated a density resolution of 4% with a central dose of 90 cGy using 90 views.
• Identified streak artifacts in reconstructions caused by metal bed support rails on the patient couch.

Conclusions:

• A standard EPID can be utilized with the Feldkamp algorithm to produce cone-beam tomographic reconstructions.
• The system shows promising density resolution for potential clinical applications.
• Further investigation is needed to mitigate artifacts arising from couch-mounted metal components.