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THE LINE FOCUS X-RAY TUBE – AN X-RAY SOURCE FOR FLASH AND SPATIALLY FRACTIONATED RADIATION THERAPY
Author Of 3 Presentations
THE LINE FOCUS X-RAY TUBE – AN X-RAY SOURCE FOR FLASH AND SPATIALLY FRACTIONATED RADIATION THERAPY
A NOVEL X-RAY SOURCE FOR MICROBEAM AND FLASH RADIOTHERAPY: NUMERICAL SIMULATIONS SHOW THE FEASIBILITY OF THE PRECLINICAL PROTOTYPE
Abstract
Background and Aims
Microbeam radiotherapy (MRT) and FLASH can widen the therapeutic window in radiotherapy. For x-ray MRT and FLASH, most research was performed at synchrotrons that are, however, unsuitable for clinical application. A promising compact source for hospitals is the line-focus x-ray tube (LFxT). We present simulations for a preclinical LFxT prototype that we are currently constructing.
Methods
To examine the dose distribution, we performed Monte Carlo simulations in TOPAS of an electron beam (300 keV, 90 kW) hitting a target made of tungsten. The phase space from electron accelerator simulations exhibited a full width at half maximum of 0.05 x 20 mm2. The produced photons traveled through a model of a custom-made, divergent multi-slit collimator (tungsten) into a water phantom. With finite element methods in COMSOL, we simulated the temperature increase at the focal spot.
Results
The microbeam dose distribution showed a divergent peak-valley profile with a peak-to-valley dose ratio of 23 and a peak dose rate of 10 Gy/s in 15 mm water depth, 200 mm from the target. The temperature increase at the focal spot was 480 K when the target surface moved at 200 m/s. Due to the narrow and fast beam, the main heat dissipation mechanism was heat capacity, contrary to heat conduction for conventional x-ray tubes.
Conclusions
Our simulations showed that the LFxT prototype produces a microbeam dose distribution suitable for preclinical MRT research. The LFxT utilizes the heat capacity limit in which the source can be scaled to a more powerful clinical source for concurrent MRT and FLASH.
A MULTISCALE AND MULTI-TECHNIQUE APPROACH FOR THE CHARACTERIZATION OF THE EFFECTS OF SPATIALLY FRACTIONATED X-RAY FLASH IRRADIATION IN LUNGS AND BRAINS
Abstract
Background and Aims
Accurate methods for monitoring the efficacy of treatments are key in radiooncology, where the quest for imaging techniques providing in three-dimensions (3D) both high spatial and contrast resolutions is incessant. X-ray Phase Contrast-Computed Tomography (XPCI-CT) is here proposed as a label-free, full-organ, multi-scale and 3D approach to study irradiated tissues with high sensitivity.
The aim is to visualize and characterize the effects of FLASH irradiations using broad beam (BB) and spatially-fractionated microbeams (MRT) with ex-vivo XPCI-CT for virtual 3D histology.
Methods
We delivered X-ray BB and MRT on healthy lungs or on healthy and glioblastoma-bearing brains of Fisher rats; irradiations were performed at the ID17 station of the European Synchrotron Radiation Facility using a dose rate of ~14000 Gy/s. After sacrificing the animals, target organs were removed, fixed and imaged by XPCI-CT using voxel sizes down to 0.73 µm3. Afterwards samples were analysed by histology, X-ray wide-angle scattering and fluorescence.
Results
XPCI-CT allowed the depiction of brain and lungs anatomical details down to the cellular level, the identification of tumour tissue, necrosis, calcifications and micrometric MRT-transections within brains and of radiation induced fibrosis in lungs. BB irradiations produced the largest amount of fibrotic tissue while MRT caused isolated scars with small iron accumulations and calcium deposits in damaged blood vessels. A complementary structural/chemical characterization of the detected structures was also achieved.
Conclusions
The proposed approach provides a supportive technique for 3D imaging-based virtual histology and for an accurate description of post-treatment conditions of biological tissues supplementing the capabilities of standard lab-based techniques.