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Testing a Tomographic Ultrasound System for Use in Small Animal Radiotherapy Guidance: A Feasibility Study

D Granville

DA Granville1*, G O'Connell2, J Butler2, M Harlacher2, J Perdomo2, T Czernuszewicz2, P Tsouchlos3, T Kanesalingam3, R Gessner2, (1) The Ottawa Hospital Cancer Centre, Ottawa, ON, (2) SonoVol, Inc., Research Triangle Park, NC, (3) Xstrahl Inc., Suwanee, GA.


SU-I-GPD-T-641 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To test the hypothesis that tomographic ultrasound, which has excellent soft tissue contrast for tumor delineation, can be used to target the delivery of small animal radiation therapy.

Methods: A benchtop ultrasound imaging system was built to accommodate a whole-animal tomographic ultrasound scan with FOV = 6 x 14 x 1 cm. Imaging frequency was 35 MHz, with spatial resolution of 44.0 um and 79.8 um axially and laterally, respectively. The transducer does not contact the tissue being imaged, resulting in no anatomical warping during 3D data acquisition. A rigid cassette was used to transport the calibration and validation phantom between the ultrasound scanner and small animal irradiator (XStrahl SARRP). Radiochromic film was used to evaluate radiation targeting efficiency. Fiducial targets, visible by ultrasound but invisible to CT, were created by etching into the radiochromic film with a precision laser cutter. Targeting coordinates were defined in the ultrasound data (N=9) and transposed into the irradiator’s coordinate space by using landmark based registration on the transfer cassette. Radiation was delivered to each target, and delivery error quantified.

Results: The phantom was scanned with the prototype ultrasound scanner in 3 min, with reconstruction time for resulting 3D volume <10 sec. Average delivery error was 0.30 ± 0.24mm across the 9 targets. The max delivery error for the targets was 0.69 mm, which is slightly greater than the manufacturer’s stated error in radiation delivery accuracy using CT guidance (0.5 mm).

Conclusion: We have demonstrated for the first time the feasibility for a workflow to use ultrasound to guide the delivery of radiation within two systems designed for use in rodent models. Future work will include the combination precision irradiation with ultrasound-derived metrics for treatment response such as tumor volume, vascularity, and molecular imaging of physiological markers for inflammation and angiogenesis.

Funding Support, Disclosures, and Conflict of Interest: Authors O'Connell, Perdomo, Butler, Harlacher, Czernuszewicz, and Gessner are employees of SonoVol, Inc., a company which is commercializing ultrasound robotic imaging systems for small animal imaging. Authors Tsouchlos and Kanesalingam are employees of Xstrahl Inc., a company which is commercializing irradiators for life science and disease research applications.

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