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The first microbeam irradiation study at the biomedical beamline SYRMEP of the Elettra-Sincrotrone Trieste, the technical setup of the experiment and the results of the associated cell culture study in murine melanoma cells are reported., It has been shown previously both in vitro and in vivo that microbeam irradiation (MBI) can control malignant tumour cells more effectively than the clinically established concepts of broad beam irradiation. With the aim to extend the international capacity for microbeam research, the first MBI experiment at the biomedical beamline SYRMEP of the Italian synchrotron facility ELETTRA has been conducted. Using a multislit collimator produced by the company TECOMET, arrays of quasi-parallel microbeams were successfully generated with a beam width of 50 µm and a centre-to-centre distance of 400 µm. Murine melanoma cell cultures were irradiated with a target dose of approximately 65 Gy at a mean photon energy of ∼30 keV with a dose rate of 70 Gy s−1 and a peak-to-valley dose of ∼123. This work demonstrated a melanoma cell reduction of approximately 80% after MBI. It is suggested that, while a high energy is essential to achieve high dose rates in order to deposit high treatment doses in a short time in a deep-seated target, for in vitro studies and for the treatment of superficial tumours a spectrum in the lower energy range might be equally suitable or even advantageous.

Conventional radiotherapy is a widely used non-invasive form of treatment for many types of cancer. However,due to a low threshold in the lung for radiation-induced normal tissue damage, it is of less utility in treating lung cancer. For this reason, surgery is the preferred treatment for lung cancer, which has the detriment of being highly invasive. Non-conventional ultra-high dose rate (FLASH) radiotherapy is currently of great interest in the radiotherapy community due to demonstrations of reduced normal tissue toxicity in lung and other anatomy. This study investigates the effects of FLASH microbeam radiotherapy, which in addition to ultra-high dose rate incorporates a spatial segmentation of the radiation field, on the normal lung tissue of rats. With a focus on fibrotic damage, this work demonstrates that FLASH microbeam radiotherapy provides an order of magnitude increase in normal tissue radio-resistance compared to FLASH radiotherapy. This result suggests FLASH microbeam radiotherapy holds promise for much improved non-invasive control of lung cancer.

Purpose This study provides the first experimental application of multiscale three-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 (MRT), a high dose rate (14 kGy/s), FLASH spatially-fractionated X-ray therapy to avoid the beamlets smearing due 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 analysed and correlated to histologic data. Results XPCI-CT enables the 3D visualization of lung tissues with unprecedented contrast and sensitivity allowing alveoli, vessels and bronchi hierarchical visualization. XPCI-CT discriminates in 3D radio-induced lesions such as fibrotic scars, Ca/Fe deposits and, in addition, allows a 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 the MRT treated organs while it reaches the 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.

International audience; BACKGROUND AND PURPOSE: To quantify the late dose-related responses of the rat cervical spinal cord to X-ray irradiations by an array of microbeams or by a single millimeter beam. MATERIALS AND METHODS: Necks of anesthetized rats were irradiated transversely by an 11 mm wide array of 52 parallel, 35 μm wide, vertical X-ray microbeams, separated by 210 μm intervals between centers. Comparison was made with rats irradiated with a 1.35 mm wide single beam of similar X-rays. Rats were killed when paresis developed, or up to 383 days post irradiation (dpi). RESULTS: Microbeam peak/valley doses of ≈357/12.7 Gy to 715/25.4 Gy to an 11 mm long segment of the spinal cord, or single beam doses of ≈146-454 Gy to a 1.35 mm long segment caused foreleg paresis and histopathologically verified spinal cord damage; rats exposed to peak/valley doses up to 253/9 Gy were paresis-free at 383 dpi. CONCLUSIONS: Whereas microbeam radiation therapy [MRT] for malignant gliomas implanted in rat brains can be safe, palliative or curative, the high tolerance of normal rat spinal cords to similar microbeam exposures justifies testing MRT for autochthonous malignancies in the central nervous system of larger animals with a view to subsequent clinical applications.