Room: AAPM ePoster Library
Purpose: To investigate a novel mechanism for measuring radiation dose in-vivo. This mechanism is based on a dose specific ultrasound imaging signal arising from a change in the material properties of a photoacoustic contrast agent following x-ray irradiation.
Methods: The effect of x-rays on the physical characteristics of a novel endoskeletal droplet designed for x-ray photoacoustic dosimetry was investigated at the microscopic scale. Droplets were irradiated with 10 MV x-rays from a medical linear accelerator. Ultrasound imaging, coherent anti-Stokes Raman scattering (CARS) and bright field (BF) microscopy were performed on samples of irradiated and non-irradiated droplets. CARS and BF images were co-registered and droplet sizes measured in each image.
Results: An increased number of the irradiated droplets exhibited detectable CARS signal (34.4% for non-irradiated versus 56.7% for irradiated droplets). Irradiated droplets displayed a statistically significant (p=0.029) increase in CARS signal density (mean value = 0.30±0.21) compared to non-irradiated droplets (mean = 0.21±0.25). Additionally, qualitative ultrasound imaging of the irradiated droplets, which were acoustically vaporized into microbubbles, showed that the acoustic response lasts for a shorter period of time. The decrease in ultrasound imaging stability and corresponding increase in the intensity of the CARS signal density post-irradiation both indicate an alteration of the material properties in the hydrocarbon endoskeleton of the droplets, possibly due to radiation-induced cross-linking/crystallinity.
Conclusions: These initial results suggest that a novel photoacoustic contrast agent may offer a mechanism for measuring radiation dose in-vivo. This mechanism is similar to polymerization that occurs in radiochromic film. Droplets could be injected prior to radiation and may yield a dose-specific acoustic signal that in combination with ultrasound imaging, would enable a true real-time 3D in-vivo dosimetry technique.
Funding Support, Disclosures, and Conflict of Interest: American Cancer Society Colorado Clinical and Translational Sciences Institute Cancer League of Colorado