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High Resolution Acoustic Angiography for Early Assessment of Tumor Response to Radiation Treatment in Rat Tumor Model

S Chang

S Chang*, R Gessner, S Wang, Y Lee, P Dayton, UNC School of Medicine, Chapel Hill, NC

WE-E-134-2 Wednesday 2:00PM - 3:50PM Room: 134

Purpose: To test the hypothesis that acoustic angiography would enable early assessment of tumor response to radiation therapy at multiple timepoints after a single-fraction radiotherapy treatment.

Methods: 15 fibrosarcoma tumor-bearing rats were irradiated (field-size:1.8x1.8cm) by 6MV photon beam from a clinical linac . Tumors were implanted subcutaneously in the lower flank area and treated 14 days later (Mean-diameter: 7.03+/-1.62mm). Animals were randomized into three groups (doses of 0, 5 or 20 Gy). Tumors were imaged prior to treatment (Day 0) using both acoustic angiography (microbubble contrast-based microvessel imaging) and standard high frequency b-mode, and then again at Days 3, 6, 9, 12, and 18. Tumor volume, and perfused volume ratio (PVR - the ratio of tumor volume with perfused voxels, to total tumor volume) were quantified at each timepoint.

Results: The tumors in the 0 or 5 Gy groups continued to grow exponentially after treatment. All animals in the 20 Gy group experienced an inflection point in their growth curve at Day 3, and tumor volume reduced exponentially until Day 12. Three of these tumors are non-responders(20Gy-NRs) and had second inflection point at Day 12, and proceeded to increase in volume, on average to their original Day 0 tumor size by Day 18. The other two tumors in the 20 Gy group are responders(20Gy-R's) and reduced to undetectable tumor volumes by Day 18. The PVR metric for vascularization revealed differences in the 20Gy-NR and 20Gy-R groups at Day 12, which correlated with tumor volumetric differences.

Conclusion: Our preliminary data indicate that the acoustic angiography-derived PVR metric can detect rat fibrosarcoma tumors responded (N=2) and those which did not (N=3) to 20 Gy radiation six days before there is a detectable difference in tumor volumes.

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