Optical Cone Beam 3D Tomography of Radiation Beams Using Cerenkov-Excited Fluorescence
A Glaser1*, S Davis1, R Zhang2, D Gladstone3, B Pogue1,2, (1) Thayer School of Engineering, Dartmouth College, Hanover, NH, (2) Department of Physics and Astronomy, Dartmouth College, Hanover, NH, (3) Dartmouth-Hitchcock Medical Center, Lebanon, NHWE-E-141-11 Wednesday 2:00PM - 3:50PM Room: 141
Purpose: Here, we explore a novel medical physics application of the Cerenkov effect for the dosimetric profiling of megavoltage beams used in radiation therapy. The technology to achieve these images has recently progressed from capturing single 2D projections with an intensified charge-coupled device, to full 3D optical tomography using parallel beam back projection and a telecentric lens. In the current study, the method is extended to 3D imaging with a standard CMOS commercial camera and lens, using cone beam tomography algorithms for the reconstruction.
Methods: Projection images of the induced Cerenkov light from a 20x20 cm² 6 MV beam operating at a dose rate of 600 MU/min incident on a water tank with a 1.0 g/L concentration of Quinine Sulfate were captured from 0-360° with a 3° angular resolution and 5.0 second exposure time, resulting in a total scan time of 10 minutes. The resulting projection images were used in a Feldkamp-Davis-Kress (FDK) cone beam tomography algorithm to reconstruct the imparted 3D dose distribution. An accuracy analysis was performed by comparing the reconstructed lateral profile at a depth of 10 cm and a percent depth dose curve to a reference dose distribution from the treatment planning system (TPS).
Results: A 3D dose distribution was successfully reconstructed from the captured projections yielding results which were within +/- 8% of the TPS dose distribution.
Conclusion: Optical cone beam 3D tomography of radiation beams using Cerenkov-excited fluorescence has been demonstrated for the first time. The proposed technique has several advantages over alternative methods (e.g., ionization chambers, scintillation, and gel dosimetry) including speed, flexibility, and necessitates only water, which serves as a cheap, abundant, and easily standardized tissue equivalent medium. Upon future refinement and improved accuracy the proposed modality may prove to be an important dosimetric tool with both clinical and research applications.