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Cerenkov Emission Tomography Using Silicon Photomultipliers

I Oraiqat1*, S DeBruin6, H Lei1 , W Zhang1, R Clarke1, I El Naqa1 (1) University of Michigan, Ann Arbor, MI (6) Endectra, LLC, Ann Arbor, MI


(Sunday, 7/29/2018) 1:00 PM - 1:55 PM

Room: Karl Dean Ballroom B1

Purpose: Cerenkov emission (CE) during external beam radiation therapy (EBRT) is limited for deep tissue dose measurements using current camera-based approaches. Therefore, we propose to place multiple Silicon Photomultiplier (SiPM) devices directly onto the skin for tomographic measurements of deep tissue CE during external beam radiotherapy. In this work, we explore the feasibility of using SiPMs to image dose by imaging deep tissue CE using a rotating SiPM device.

Methods: CE is generated using 6MV photons with 5x5cm and 5x2cm field sizes inside two gelatin-based cylindrical optical phantoms (a diameter of 100mm and a thickness of 50mm) that simulate a breast cross section. One phantom is transparent while the other phantom has TiO2 powder homogeneously mixed inside (1 g/L) to add optical scattering to mimic breast tissue. To simulate a multitude of probes placed at various locations on a surface using a single SiPM detector (1x1mm sensor size), a 1x1mm region of the phantom surface is imaged onto the detector using an achromatic lens, simulating a direct placement of the SiPM onto the surface. A mechanical C-arm is used to rotate the SiPM probe around the phantom to collect intensity measurements at the surface every 1.2° for 360°. Data acquisition is gated to the target output of the Linac. This dataset is transformed into line profiles at each angle by accounting for lens divergence. An inverse Radon transform (using the Shepp-Logan filter) is used for the 2D image reconstruction.

Results: The shape of the field was recovered in both clear and scattering optical phantoms. The aspect ratios for the two shapes measured are within 1% and 3% of the 5x5cm field (for the clear and scattering phantom, respectively) and 2.5% and 5% for the 5x2cm field.

Conclusion: This work shows the potential for tomographic reconstruction of CE within scattering media.

Funding Support, Disclosures, and Conflict of Interest: This research was partly supported by Endectra, LLC.


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