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3D Dosimetry with a Novel Optical CT Scanner Using Fiber Optic Taper for Collimated Images

C Wuu1*, Y Wang1, O.M. Dona Lemus1, X Qian2, J Adamovics3, A Xu1, (1) Depart of Radiation Oncology, Columbia Univ Medical Center, New York, NY, (2) Depart of Radiation Oncology, Stony Brook Univ Hospital, Stony Brook, NY, (3) Depart of Chemistry, Rider Univ, Lawrenceville, NJ.


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: A novel broad-beam optical CT scanner, using fiber optic taper for collimated images, was developed as a fast, high resolution, and accurate 3D dosimetric tool for patient specific IMRT QA.

Methods: The optical CT scanner incorporates a telecentric illuminator with parallel red-light beam, an aquarium filled with optical matching fluid to the refractive index of the PRESAGE phantom, a fiber optic taper for collimation of transmitted light, and a CCD camera. Stray light due to scatter, reflections, and refractions are removed due to the collimation effect of the fiber optic taper. The effect of collimation on the 3D dose measurement was studied. Spatial resolution, Modulate-Transfer-Function (MTF), Signal-to-Noise-Ratio (SNR), and image distortion tests were performed. Dose distribution comparison between the broad-beam optical scanner using fiber optic taper and the “gold standard” single-beam optical scanner was performed for square field, conformal arc, and IMRT field measurements. The 2D dose distributions generated by the broad–beam scanner were also compared to EBT3 results.

Results: With collimated images from fiber optic taper, the highest spatial resolution is estimated to be 0.07mm with MTF 10%. The scanning time for a complete 3-D dataset acquisition is less than 10 minutes. For dose distribution comparison, using conformal arc small fields, the gamma passing rate (2%/2mm criteria, 10% dose threshold) was 100% between the fast broad-beam CT scanner and EBT3, and 99% between the broad-beam scanner and the single-beam scanner. All the dose distributions from the broad-beam optical scanner were reconstructed directly from the 2D projected images without any correction for stray light. The stray light was removed almost completely through the collimation effect of fiber optic taper.

Conclusion: The newly designed broad-beam optical CT scanner, utilizing fiber optic taper for collimation of transmitted lights, can provide a fast, high resolution, and accurate dose readout of 3D dosimeters.

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