Technical Note: Radiotherapy dose characterization of gel dosimetry using shear wave elasticity imaging

Area of Science:

• Medical Physics
• Radiotherapy
• Biomedical Engineering

Background:

• Radiotherapy is a cornerstone cancer treatment.
• Conventional dosimetry methods have limitations in capturing 3D dose distributions.
• Gel dosimetry offers potential for 3D dose mapping due to radiation-induced changes in material properties.

Purpose of the Study:

• To quantitatively measure radiation dose in N-isopropylacrylamide (NIPAM) gel dosimeters using ultrasonic shear wave elasticity imaging (SWEI).
• To assess the correlation between gel elasticity and radiation dose.
• To evaluate SWEI as a non-destructive tool for 3D dose distribution analysis in gel dosimetry.

Main Methods:

• NIPAM polymer gel phantoms were irradiated with varying doses (0-10 Gy) using a 6 MV linear accelerator.
• Gel phantoms were analyzed using SWEI at 24, 36, and 48 hours post-irradiation.
• Two-dimensional (2D) shear wave velocity and Young's modulus maps were reconstructed to represent dose distribution, with a spatial resolution of approximately 1 mm.

Main Results:

• A linear increase in elastic modulus with increasing radiation dose was observed (R² values of 0.94-0.98).
• Gel elasticity showed a strong association with radiation dose, particularly at 36 hours post-irradiation.
• The dose resolution was determined to be 0.66 kPa/Gy, and 3D dose distribution was reflected in the elastic modulus maps.

Conclusions:

• SWEI successfully provided quantitative, non-destructive measurement of radiation dose in NIPAM gel dosimetry.
• Gel elasticity is highly correlated with x-ray irradiation dose.
• Future work includes measuring and reconstructing 3D dose distributions from intensity-modulated radiotherapy (IMRT) and comparing with treatment planning system (TPS) data.