Radiation dose imaging with ultrasound shear-wave elastography and radiation sensitive gels

Abstract

Radiation sensitive gels have been investigated for use in radiation dosimetry for a number of years. Previously we have determined the applied dose distribution by measuring the radiation induced stiffness distribution with quantitative quasistatic ultrasound elastography. Here, a preliminary assessment of shear-wave elastography for radiation dose measurement is presented. A block of radiation sensitive gel was irradiated along one of its axis to produce a high-dose stiff rod-like inclusion. The Young's modulus distribution was measured applying the Aixplorer <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> ultrasound scanner in regions of interests (ROI) in various planes orthogonal to the axis of irradiation. Medium filtering for ¿salt and pepper¿-noise reduction, and averaging the Young's modulus distributions from a number of planes orthogonal to the direction of the irradiation improved the image quality, e.g. the elevated Young's modulus in the irradiated regions was clearly detected, and the dimensions and shape of the irradiated area preserved. The applied method had several advantages compared to the quasi-static approach. The method was easy to use because of the rapid and direct measurement of Young's modulus without the need of an inverse reconstruction and user interaction. Also, no boundary effects were detected. Promise also lies in the foreseeable development of the shearwave modality into 3D. The scanner hardware and the shearwave measurement routine may be adjusted for the needs of gel dosimetry to achieve a higher penetration depth and improve the accuracy for example by creating a denser mesh of radiation force pushes. Quantitative dose measurements may be possible by converting the measured Young's modulus distribution into a dose distribution by applying a calibration.