Exhibit Hall | Forum 6
Purpose: Radiation dose amplification with nanoparticles can increase cancer cell death without increasing toxicity risk to healthy tissues. AGuIX nanoparticles, incorporating gadolinium atoms, are currently under clinical investigation at several centers for MR-guided radiotherapy. However, MR imaging is not readily available in all radiotherapy clinics. In the present study, we investigate conventional clinical CT, operating at different tube energies, to visualize and quantify nanoparticle concentration in a novel phantom.
Methods: The phantom is a 16.5 cm diameter cylinder filled with water as well as of eight smaller cylinders containing saline and concentrations of AGuiX with values of 0, 0.01, 0.05, 0.1, 0.2, 0.5, 1, and 5 mg/ml. CT scans were acquired at energies from 80 to 140 kVp and reconstructed using standard clinical algorithms to evaluate HU for each concentration. A two-material decomposition algorithm was employed using the scans at 80 and 140 kVp. The saline and AGuiX material coefficients were estimated by an iterative penalized least squares calculation. A Huber roughness penalty function was applied between the coefficient values in neighboring pixels.
Results: AGuiX concentration showed a linear relationship with HU (R^2=0.98). For the lowest concentrations evaluated, noise was a factor in the measurement. After material decomposition, the different AGuIX samples had qualitatively different intensities, as well as a linear relationship between concentration and material coefficient (R^2=0.95). Noise at low levels was improved with a statistically significant difference found between saline-only and 0.1mg/ml AGuiX.
Conclusion: Conventional radiotherapy CT scans may offer a means of effectively quantifying nanoparticle concentration. Future investigation will focus upon incorporating higher Z material in the nanoparticle, which may further improve signal detection.