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Preliminary Characterization of Microbeam Radiation Using Very High Resolution 3D Dosimetry


T Juang

T Juang1*, R Ger2, Q Li1, M Hadsell2, J Adamovics3, O Zhou2, M Oldham7, S Chang2, (1) Duke University, Durham, NC, (2) University of North Carolina - Chapel Hill, Chapel Hill, NC, (3) Rider University, Lawrenceville, NJ

SU-D-144-7 Sunday 2:05PM - 3:00PM Room: 144

Purpose:
Compact microbeam radiation therapy (MRT) recently became feasible through the development of carbon-nanotube based distributed x-ray array technology. This work investigates the feasibility of novel high-resolution 3D dosimetry techniques (50μm isotropic) for the challenging task of characterizing microbeam irradiations of nominal width 300-400μm.

Methods:
A cylindrical PRESAGE 3D dosimeter (20mm diameter, 22mm long) was irradiated with three parallel microbeams generated by a prototype compact MRT system for small animal research developed at UNC. The carbon nanotube field emission x-ray source array is designed to produce x-rays up to 160 kV which are collimated to microbeam radiation through an external collimator. The entrance dose used in this study was estimated from EBT2 film to be 32 Gy. A 50μm isotropic 3D dose distribution was obtained by imaging the dosimeter in the Duke Micro Optical-CT Scanner (DMicrOS), an in-house, bi-telecentric optical CT system optimized for high-resolution optical tomography. Preliminary analysis of microbeam characteristics was performed on a ROI averaged across the central 10mm of the dosimeter. Beam width (FWHM), percent depth dose (PDD), and peak-to-valley dose ratio (PVDR) were measured as a function of depth along the irradiated beam paths.

Results:
Beam width measurements indicated that the average FWHM across all three beams remained constant (405.3μm, σ=13.2μm) between depths of 3.00-14.00mm. PDD measurements were normalized to values at 3.00mm depth (to avoid bias due to possible optical artifact at the dosimeter surface) and showed a falloff to 82.9-90.5% at 14.00mm depth. PVDR increased with depth from 6.3 at 3.00mm depth to 8.6 at 14.00mm depth.

Conclusion:
These preliminary results from the DMicrOS/PRESAGE 3D dosimetry system show strong potential for uniquely comprehensive verification of microbeam irradiations. Future work is required to investigate the potential of stray-light artifacts in this extreme geometry.


Funding Support, Disclosures, and Conflict of Interest: NIH R01CA100835

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