X-ray CT dose in normoxic polyacrylamide gel dosimetry

Area of Science:

• Medical Physics
• Radiological Physics
• Polymer Science

Background:

• Normoxic polyacrylamide (nPAG) gel dosimeters are used for dose measurement.
• X-ray computed tomography (CT) is a common imaging modality.
• Understanding the effects of CT imaging dose on nPAG is crucial for accurate dosimetry.

Purpose of the Study:

• To quantify the absorbed CT dose in nPAG gel dosimeters.
• To determine the dose response of nPAG to CT imaging photon energies.
• To calculate the induced change in CT number (deltaN(CT)) in nPAG due to CT imaging.

Main Methods:

• Quantification of absorbed CT dose in nPAG under various CT imaging protocols.
• Raman spectroscopy to establish nPAG response to 120-140 kVp photons and comparison with 6 MV photons.
• Calculation of induced deltaN(CT) based on absorbed dose and dose response data.

Main Results:

• Maximum absorbed CT dose in nPAG is approximately 4.6 cGy/image, scaling linearly with image averaging.
• nPAG shows a weaker dose response to 140-kVp photons compared to 6 MV photons.
• Typical CT imaging protocols induce deltaN(CT) < 0.2 H, below the detection limit; expanded protocols may induce deltaN(CT) ~0.5 H.

Conclusions:

• The CT imaging dose in nPAG gel dosimeters is generally low under typical protocols.
• Induced polymerization due to CT imaging may need consideration for high-dose or high-average imaging protocols.
• Further investigation into the impact of imaging parameters on nPAG dosimetry is warranted.