Development of a micro-computed tomography-based image-guided conformal radiotherapy system for small animals.

Abstract

To report on the physical aspects of a system in which radiotherapy functionality was added to a micro-computed tomography (microCT) scanner, to evaluate the accuracy of this instrument, and to and demonstrate the application of this technology for irradiating tumors growing within the lungs of mice. A GE eXplore RS120 microCT scanner was modified by the addition of a two-dimensional subject translation stage and a variable aperture collimator. Quality assurance protocols for these devices, including measurement of translation stage positioning accuracy, collimator aperture accuracy, and collimator alignment with the X-ray beam, were devised. Use of this system for image-guided radiotherapy was assessed by irradiation of a solid water phantom as well as of two mice bearing spontaneous MYC-induced lung tumors. Radiation damage was assessed ex vivo by immunohistochemical detection of gammaH2AX foci. The positioning error of the translation stage was found to be <0.05 mm, whereas after alignment of the collimator with the X-ray axis through adjustment of its displacement and rotation, the collimator aperture error was <0.1 mm measured at isocenter. Computed tomography image-guided treatment of a solid water phantom demonstrated target localization accuracy to within 0.1 mm. Gamma-H2AX foci were detected within irradiated lung tumors in mice, with contralateral lung tissue displaying background staining. Addition of radiotherapy functionality to a microCT scanner is an effective means of introducing image-guided radiation treatments into the preclinical setting. This approach has been shown to facilitate small-animal conformal radiotherapy while leveraging existing technology.