X-Ray Phase Contrast 3D Virtual Histology: Evaluation of Lung Alterations After Microbeam Irradiation

Purpose: This study provides the first experimental application of multiscale 3-dimensional (3D) x-ray phase contrast imaging computed tomography (XPCI-CT) virtual histology for the inspection and quantitative assessment of the late-stage effects of radio-induced lesions on lungs in a small animal model. Methods and Materials: Healthy male Fischer rats were irradiated with x-ray standard broad beams and microbeam radiation therapy, a high-dose rate (14 kGy/s), FLASH spatially fractionated x-ray therapy to avoid beamlet smearing owing to cardiosynchronous movements of the organs during the irradiation. After organ dissection, ex vivo XPCI-CT was applied to all the samples and the results were quantitatively analyzed and correlated to histologic data. Results: XPCI-CT enables the 3D visualization of lung tissues with unprecedented contrast and sensitivity, allowing alveoli, vessel, and bronchi hierarchical visualization. XPCI-CT discriminates in 3D radio-induced lesions such as fibrotic scars and Ca/Fe deposits and allows full-organ accurate quantification of the fibrotic tissue within the irradiated organs. The radiation-induced fibrotic tissue content is less than 10% of the analyzed volume for all microbeam radiation therapy–treated organs and reaches 34% in the case of irradiations with 50 Gy using a broad beam. Conclusions: XPCI-CT is an effective imaging technique able to provide detailed 3D information for the assessment of lung pathology and treatment efficacy in a small animal model.