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Investigation of Tumor Vascular Response to Microbeam Radiation Therapy Compared to Conventional Radiation Using High-Resolution Quantitative Ultrasonic Microvascular Imaging

J Rivera

J Rivera1,2*, S Kasoji1,2 , R Gessner3, P Dayton1,2,3 , S Chang2 , (1) UNC Chapel Hill / NC State University, Chapel Hill, NC, (2) UNC School of Medicine, Chapel Hill, NC, (3) SonoVol LLC, Chapel Hill, NC


TH-AB-FS4-8 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 4

Purpose: Microbeam radiation therapy (MRT) is an experimental treatment that has been shown to eradicate tumors without damaging the function of normal tissues exposed to the same high dose radiation in animal studies. One barrier for clinical translation of this promising treatment approach is a lack of understanding of its working mechanism. We have shown previously that MRT alters tumor microvasculature differently than conventional broad beam radiation (BRT). We propose to use Acoustic Angiography (AA), a novel ultrasound imaging modality, to perform a longitudinal study on tumor microvasculature response to radiation. The study will allow us to take one step further in understanding the working mechanism behind MRT.

Methods: Fisher 344 rat fibrosarcoma tumor model was used. Thirteen (N=13) rats were surgically implanted with tumor tissue in the right flank and allowed to progress naturally until tumors reached target size. Rats were divided into 3 cohorts and treated with single-dose radiation (n=6, 15Gy BRT, n=5, 100Gy MRT (peak dose), n=2 control (untreated)). MRT beams were produced using a research irradiator (Precision X-Rays Inc.) with custom built collimator. All tumors were imaged using traditional B-mode ultrasound and AA at pre-treatment baseline and every 3 days thereafter. Both tumor volume (TV) and volumetric vascular density (VVD) measurements were taken and analyzed at each time point.

Results: Control tumors had large increases in TV and VVD over time one week post-treatment. BRT-treated tumors had significant decreases in TV as well as VVD. The TV for MRT-treated tumors indicate that MRT induces partial tumor control, although less-so than for BRT-treated tumors; however, the overall VD is higher.

Conclusion: We have demonstrated that vascular density analysis of MRT-treated tumors is feasible using the novel quantitative Acoustic Angiography technique and present relevant results and statistics. Furthermore, MRT-treated tumors appear to react differently than BRT-treated tumors.

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