X-ray microbeam radiation therapy (MRT) is a promising new approach to treating cancers by irradiation, as MRT can destroy entire tumors with far less damage to adjacent normal tissues than can conventional x-ray radiotherapy methods. MRT uses highly collimated planes of x-rays with about 70 keV energy generated by synchrotron sources. The arrays of microbeams, with a typical thickness of 50 μm and a separation of 400 μm, consist of a series of peaks with high doses and valleys with low doses (ideally zero dose) shaped like a comb. Microbeam dosimetry is vital to ensure beam quality if MRT is to be used on human patients. Measurements of the dose both in the microbeams (the peaks) and between them (the valleys) are necessary for treatment plans.
Currently, quality assurance is performed using radiochromic film measurements, microdiamond detectors, and semiconductor devices, which all have their limitations. Tissue/water equivalency is an extremely desirable property for a dosimeter to have in a clinical setting, as the tissue/water equivalent dose is usually the dosimetric quantity in question. Therefore, development of high-spatial resolution and tissue/water-equivalent micro-dosimeters is vitally important for clinical acceptance of MRT. In response, researchers at the University of Wollongong (UOW; Wollongong, Australia) and the Australian Synchrotron (Clayton, Australia) have developed the first high-spatial resolution and tissue/water-equivalent fiber-optic dosimeters able to meet the requirements and challenges of MRT applications.
The fiber-optic dosimeters use plastic scintillators as the radiation conversion material and plastic optical fibers as the transmission media. The materials of both the plastic scintillator and fibers are tissue/water-equivalent. The device has a spatial resolution of 50 μm, allowing microstructures of individual microbeams to be resolved and the peak-to-valley dose ratio and the full width at half maximum of the microbeams measured. The results were compared to a semiconductor strip detector of the same spatial resolution. A percent depth dose was measured and also compared to data acquired by an ionization chamber. The results achieved so far demonstrate significant steps towards the development of optical dosimeters, with the potential to be applied in quality assurance of microbeam radiation therapy. A 20 μm fiber-optic dosimeter has also been developed and tested, with results to be published soon. The final goal is to design and construct fiber-optic dosimeters with 10 μm spatial resolution. Reference: J. Archer et al., Sci. Rep. (2017); doi:10.1038/s41598-017-12697-6, or contact Enbang Li at [email protected].