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Linear Accelerator-Based, Submillimeter Treatment Technique: Can We Reproduce Microbeam Radiobiology Experiments Using a Common Radiotherapy Accelerator?

R Shaw

R Shaw*, D Siergiej , R Goodman , R Selwyn , University of New Mexico, Albuquerque, NM


SU-I-GPD-T-645 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Microbeam radiation therapy (MRT) is a preclinical cancer treatment that could be ideal for treating resistant cancers such as glioblastoma. Evidence has shown that MRT provides differential sparing of normal verses cancer tissues. Explanations of the effect include differences in vasculature generation/repair, distinctive genetic sensitivity, bystander effects, and immune system stimulation. However, the majority of these conclusions have been generated using large synchrotron facilities with slits of radiation that range from tens to hundreds of microns and dose rates that are up to 10 times larger than conventional radiation therapy. Recently, attempts have been made to make MRT more available by using cheaper/ubiquitous radiation sources but accepting lower beam output and large beam widths. We demonstrate a technique of delivering an array of sub-millimeter beams using a conventional linear accelerator.

Methods: An applicator typically used for en face electron radiation therapy is modified to hold a slit collimator. The slit is created using shims approximately 70 microns thick placed between two tungsten plates. Beam output and field width are measured with radiochromic film at different depths in a water equivalent phantom. Reproducibility is tested by recreating the setup six times. As a demonstration on how this technique will be used for experiments, an array of slits is created by translating the phantom between exposures.

Results: The average measured beam width is 850 microns (standard deviation 0.0084) at 1.5cm depth. The narrowest field is measured at the phantom’s surface 322 microns (standard deviation 0.0090) and increases to nearly 1000 microns at 10 cm depth. At 1.5cm depth, the average measured output is 0.072 cGy/MU (standard deviation 0.012).

Conclusion: This technique shows promise in performing MRT experiments utilizing conventional radiotherapy equipment. Future experiments will be to (1.)reproduce prior MRT results (2.)create the first MRT radiobiology model for the liver.

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