Fixed, object-specific intensity compensation for cone beam optical CT radiation dosimetry.

Area of Science:

• Medical Physics
• Radiological Sciences
• Optical Imaging

Background:

• Optical cone beam computed tomography (CT) offers fast, accurate 3D radiation dosimetry using radiochromic gel dosimeters.
• High initial attenuation in large-volume gels (⩾10 cm diameter) limits signal intensity and gel re-use.
• Current methods restrict measurements to the lower 10%-20% of the camera sensor's dynamic range.

Purpose of the Study:

• To introduce a simple, inexpensive method for creating source compensators to overcome attenuation issues in optical CT dosimetry.
• To demonstrate the effectiveness of these compensators in improving signal intensity and enabling the imaging of larger gel volumes.
• To facilitate the re-use of radiochromic gel dosimeters by mitigating transmission loss.

Main Methods:

• Developed printable source compensators on transparent films, analogous to bowtie filters in x-ray CT.
• Implemented compensators beyond the focal zone of the imaging lens to prevent reconstruction artifacts.
• Evaluated the technique using transmission images and solution phantom reconstructions.

Main Results:

• Compensators successfully reduced the range of intensities in projection images, improving the measurable dose range.
• Demonstrated the prevention of high spatial frequency artifacts from printed film features.
• Enabled imaging of larger gel volumes (approximately 15 cm diameter) and facilitated dosimeter re-use.

Conclusions:

• Printable source compensators are an effective and inexpensive solution to the attenuation problem in large-volume radiochromic gel dosimetry.
• This technique significantly enhances the capabilities of optical CT dosimetry, allowing for larger sample sizes and improved experimental efficiency.
• The method paves the way for wider adoption of 3D optical dosimetry in radiation research and applications.