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X-Ray Fluorescence Imaging Guided Microbeam Radiation Therapy

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P Chtcheprov

P Chtcheprov*, M Hadsell, L Burk, R Ger, C Inscoe, H Yuan, S Chang, J Lu, O Zhou, University of North Carolina, Chapel Hill, NC

WE-E-108-4 Wednesday 2:00PM - 3:50PM Room: 108

Purpose:
We demonstrate the feasibility of x-ray fluorescence for quick and accurate image guidance for targeted irradiation of small animal tumor models in Microbeam Radiation Therapy (MRT).

Methods:
A reduced-dose treatment beam excites x-ray fluorescence from contrast agents preferentially-accumulating at tumor sites. Intensity profiles of the fluorescence signal are mapped as the mouse injected with the contrast agent is moved through the field of view. The tumor location is identified as the regions with high fluorescence intensities.
For this feasibility study, our compact small-animal MRT system and a mouse head phantom were used. The MRT device uses a carbon nanotube (CNT) field emission x-ray source array operating at 160kVp and adjustable-width external collimator to generate microbeam radiation at a microbeam dose rate of ~1Gy/min.
A phantom consisting of an acrylic rod inserted into a mouse skull accurately represents the attenuation of the head. The rod contains ~1.5mm diameter holes separated by 4mm, filled with 12mg/mL iodine solution, similar to the reported tumor concentration from IC injection. The phantom was translated through the treatment beam in 600um steps, 20 seconds per step. The fluorescence signal was recorded using a slit-collimated spectrum analyzer.

Results:
Processed spectra displayed fluorescent intensity peaks corresponding with locations of iodine solution in the phantom. The FWHMs of these peaks are 1.78mm and 1.72mm. The actual diameters of corresponding regions are 1.56mm and 1.47mm, indicating ~250um uncertainty.

Conclusion:
Preliminary results demonstrated feasibility of x-ray fluorescence for guidance in MRT. The acquisition time for a 15mm head phantom is ~8 minutes, within the reported retention time of the contrast agent. ~250um uncertainty is comparable to results from our in vivo brain tumor-bearing mouse experiment using MRI and x-ray image guidance. The x-ray fluorescent method is substantially faster. The process will be further optimized and validated with in-vivo studies.

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