TRACKING DOWN ALPHA-PARTICLES: THE DESIGN, CHARACTERISATION AND TESTING OF A SHALLOW-ANGLED ALPHA-PARTICLE IRRADIATOR

Stereotactic implantation of diffusing alpha-emitters radiation therapy sources in the swine brain: a potential new focal therapy for brain tumors

PURPOSE

Diffusing alpha-emitters Radiation Therapy ("Alpha DaRT") is a new cancer treatment modality that employs radium-224-loaded metal sources implanted in solid tumors to disperse alpha-emitting atoms within a therapeutic "kill-zone" of a few millimeters around each source. Preclinical studies have demonstrated tumor growth delay in various cancer types, including glioblastoma multiforme, and the method is used in clinical trials for patients with skin and head and neck cancer. This study aims to assess the safety and feasibility of implementing Alpha DaRT for brain tumor treatment in a large animal model.

METHODS

Alpha-DaRT sources were delivered via image-guided stereotactic implantation into both hemispheres of eight swine. 1-3 layers of radial deployment of 7 sources were delivered through a single penetration point into each hemisphere. A 90-day follow-up period included clinical evaluation, brain MRI, head CT, blood, CSF, urine, and feces sampling, and an analysis of source location over time. Brain tissue pathology was performed on termination.

RESULTS

Alpha-DaRT sources were reproducibly and efficiently delivered to the brain cortex and subcortex. No unexpected abnormalities were detected in blood or CSF samples. MRI and CT scans revealed no evidence of major bleeding or infection. Measurements of 212Pb in blood and CSF exhibited the expected exponential decay from day 7 to day 14 post-source implantation. Minimal spatial and temporal movements of the sources were noted. Histopathological analysis demonstrated locally confined findings in brain parenchyma in a very close proximity to the sources.

CONCLUSION

Alpha-DaRT sources can be safely delivered into a large animal brain using image-guided stereotactic implantation. These findings support further exploration of Alpha DaRT as a potential treatment modality for brain tumors.

Modeling of dose and linear energy transfer homogeneity in cell nuclei exposed to alpha particles under various setup conditions

PURPOSE

Different alpha exposure setups are often used to study the relation between biological responses and LET. This study aimed to estimate the dose heterogeneity and uncertainty in four exposure setups using Geant4 and PARTRAC codes. The importance of the irradiation system characteristics was shown in the context of reporting experimental results, especially in radiobiological studies at the molecular level.

MATERIALS AND METHODS

Geant4 was used to estimate the dose distributions in cells grown on a disk exposed to alpha particles penetrating from above and below. The latter setup was simulated without and with a collimator. PARTRAC was used for the validation of Geant4 simulations based on distributions of the number of alpha particles penetrating a round nucleus and the deposited energy.

RESULTS

The LET distributions obtained for simulated setups excluding the collimator were wide and non-Gaussian. Using a collimator resulted in a Gaussian LET distribution, but strongly reduced dose rate and dose homogeneity. Comparison between PARTRAC and Geant4 calculations for the cell nucleus exposed to alpha radiation showed an excellent agreement.

CONCLUSIONS

The interpretation of results from radiobiological experiments with alpha particles should always cover the characteristics of the experimental setup, which can be done precisely with computational methods.

Construction and evaluation of an α-particle-irradiation exposure apparatus

PURPOSE

The development of an exposure apparatus for in situ α-irradiation studies of cells. The construction of the apparatus is simple and the apparatus is maintenance free, easy to use and of low cost. This small device can be placed in an incubator, where the exposure environment is controlled. Moreover the vapor saturated incubator protects the cells from drying out, allowing long irradiation intervals.

MATERIALS AND METHODS

The system includes a ²³⁴U alpha (α)-source of total activity 0.77 ± 0.03 MBq in the form of a thin disk deposited on an aluminum substrate. The α-particles emitted in the air have a mean energy of 4.9 MeV at the disk surface. Source homogeneity has been studied via Rutherford Backscattering Spectrometry. Using SRIM 2013 and Monte Carlo (MC) simulations via the MCNP6.1 code, LET and energy deposition values have been calculated for various filling gasses. Furthermore, based on these simulations, the assembly's dimensions and equivalent irradiation rate have been determined. With respect to the aforementioned dimensions, the experimental setup is constructed in a way to provide uniform irradiation of the sample. Using Sacalc3v1.4 irradiation radial homogeneity has been studied. In order to evaluate biologically our apparatus, a well-established chromosomal aberration assay has been utilized, applied in exponentially growing hamster (CHO) cells. Furthermore, immunofluorescence gamma-H2AX/53BP1 foci assay has been performed as a 'biological detector', in order to validate α-particles surface density.

RESULTS

Source surface homogeneity: emission deviations do not exceed 10-15%. The optimal distance between the source and the cells for irradiation is determined to be 14.8 mm. Irradiation radial homogeneity: a deviation of 5% occurs at the first 8 mm from the center of the irradiation area, and a 10% deviation occurs after 12 mm. Chromosomal aberrations were found in good agreement with the corresponding in bibliography.

CONCLUSIONS

The current technical report describes analytically the development and evaluation stages of this experimental housing; from MC simulations to the irradiation of mammalian cells and data analysis. Moreover, guidance is provided as well as a report of the variables on which critical parameters are depended, so as to make this work useful to anyone who wants to construct a similar in-house α-irradiation apparatus for radiobiological studies using mammalian cells.

Small is beautiful: low activity alpha and gamma sources for small-scale radiation protection research experiments

PURPOSE

Uncertainties regarding the magnitude of health effects following exposure to low doses of ionizing radiation remain a matter of concern both for professionals and for the public. There is consensus within the international radiation research community that more research is required on biological effects of radiation doses below 100 mGy applied at low dose rates. Moreover, there is a demand for increasing education and training of future radiation researchers and regulators. Research, education and training is primarily carried out at universities but university-based radiation research is often hampered by limited access to radiation sources. The aim of the present report is to describe small and cost-effective low activity gamma and alpha sources that can easily be installed and used in university laboratories.

METHODS AND RESULTS

A gamma radiation source was made from an euxenite-(Y) rock (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6) that was found in an abandoned mine in Sweden. It allows exposing cells grown in culture dishes to radiation at a dose rate of 50 µGy/h and lower. Three alpha sources were custom-made and yield a dose rate of 1 mGy/h each. The construction, dosimetry and cellular effects of the sources are described.

CONCLUSIONS

We hope that the report will stimulate research and training activities in the low dose field by facilitating access to radiation sources.

Large Field Alpha Irradiation Setup for Radiobiological Experiments

The use of alpha particles irradiation in clinical practice has gained interest in the past years, for example with the advance of radionuclide therapy. The lack of affordable and easily accessible irradiation systems to study the cell biological impact of alpha particles hampers broad investigation. Here we present a novel alpha particle irradiation set-up for uniform irradiation of cell cultures. By combining a small alpha emitting source and a computer-directed movement stage, we established a new alpha particle irradiation method allowing more advanced biological assays, including large-field local alpha particle irradiation and cell survival assays. In addition, this protocol uses cell culture on glass cover-slips which allows more advanced microscopy, such as super-resolution imaging, for in-depth analysis of the DNA damage caused by alpha particles. This novel irradiation set-up provides the possibility to perform reproducible, uniform and directed alpha particle irradiation to investigate the impact of alpha radiation on the cellular level.