Characterization of speckle in lung images acquired with a benchtop in-line x-ray phase-contrast system.

We investigate the manifestation of speckle in propagation-based x-ray phase-contrast imaging of mouse lungs in situ by use of a benchtop imager. The key contributions of the work are the demonstration that lung speckle can be observed by use of a benchtop imaging system employing a polychromatic tube-source and a systematic experimental investigation of how the texture of the speckle pattern depends on the parameters of the imaging system. Our analyses consists of image texture characterization based on the statistical properties of pixel intensity values.

SU-E-J-05: Validation of an Iterative Tomosynthesis Algorithm for Low Dose on Board Cone Beam CT Patient Localization.

PURPOSE: Cone beam CT (CBCT) is a well established technique to localize patients using bone and soft tissue anatomy. Current protocols are limited to one weekly CBCT due to the considerable imaging dose delivered to the patient. The purpose of this project is to develop and validate a low dose CBCT algorithm to reduce dose and imaging time of current 3D imaging localization procedures using a novel iterative tomosynthesis algorithm to allow daily CBCT for patient positioning and target localization. METHODS: The algorithm is based on the combination of a tomosynthesis filtered back propagation (TFBP) acquisition geometry algorithm and a maximum likelihood expectation maximization (MLEM) iterative reconstruction. Circular or arc acquisition trajectory, projection number, and angular projection position are optimized according to the anatomical treatment site and region of interest. The TFBP method provides the first 3D image estimate, and the MLEM improves its quality. In this study, we focused on head and neck treatment localization imaging. RESULTS: We studied the performance of our tomosynthesis algorithm imaging resolution on an anthropomorphic head and neck phantom to determine image quality as a function of dose reduction techniques. Reconstructed anatomy shows that a 1/8 dose reduction provides similar image quality and resolution as current CBCT protocols. Seven iterations show an optimal compromise between image quality and reconstruction time. Tomosynthesis images provide digitally reconstructed radiographs with similar resolution and contrast as full CBCT. We verified that the iterative process eliminates phantom images originated by the acquired sparse angular data projections. CONCLUSIONS: We developed and validated an iterative algorithm for low dose cone beam CT based on circular or arc tomosynthesis geometries and iterative reconstruction techniques. The algorithm combines the strengths of both techniques to provide a novel low dose method to image patient anatomy for patient positioning and target localization.

SU-E-T-159: Sensitivity of in Line Real Time Scintillating Fiber Detectors for External Beam Treatment Verification and Patient Safety.

PURPOSE: We studied the sensitivity of a novel transmission fiber scintillator array designed and built for in line treatment verification. The purpose of this project is to assess the capability of the fiber detector array technology to detect treatment errors in real time without false positives to enhance patient safety. METHODS: We developed a linear scintillator array detector using radiation hard scintillating fibers and high speed parallel signal conditioning and data acquisition to monitor external beam treatment fluence in real time. The detector captures and resolves the time and amplitude of each linac pulse at each MLC segment. The detector has 60 fibers aligned to each MLC leaf and two output channels per fiber. The data is captured by a high speed parallel digitizer to determine the IMRT beam output delivered to a patient in real time. We evaluated the detector peak pulse linearity according to dose rate, MLC positioning, and beam energy. We analyzed the detector sensitivity, signal to noise ratio, and pulse distribution statistics to determine beam output and fluence in real time. RESULTS: We analyzed the response of the detector to 6 MV and 10 MV photon beams. The statistical analysis of the detected linac pulses indicates that a minimum of 20 pulses are required to evaluate MLC positioning and fluence with 3 mm and 3% resolution, respectively. During testing, no false positives were detected. Linearity with respect to output rate, MLC or jaw opening, and fluence is within 2%. CONCLUSIONS: Measured sensitivity and signal to noise ratio of a real time linear fiber array detector show that delivered beam fluence can be monitored every 55 msec, with no observed false positives during treatment to provide in vivo real time patient safety and beam monitoring.

MicroRT-small animal conformal irradiator.

A novel small animal conformal radiation therapy system has been designed and prototyped: MicroRT. The microRT system integrates multimodality imaging, radiation treatment planning, and conformal radiation therapy that utilizes a clinical 192Ir isotope high dose rate source as the radiation source (teletherapy). A multiparameter dose calculation algorithm based on Monte Carlo dose distribution simulations is used to efficiently and accurately calculate doses for treatment planning purposes. A series of precisely machined tungsten collimators mounted onto a cylindrical collimator assembly is used to provide the radiation beam portals. The current design allows a source-to-target distance range of 1-8 cm at four beam angles: 0 degrees (beam oriented down), 90 degrees, 180 degrees, and 270 degrees. The animal is anesthetized and placed in an immobilization device with built-in fiducial markers and scanned using a computed tomography, magnetic resonance, or positron emission tomography scanner prior to irradiation. Treatment plans using up to four beam orientations are created utilizing a custom treatment planning system-microRTP. A three-axis computer-controlled stage that supports and accurately positions the animals is programmed to place the animal relative to the radiation beams according to the microRTP plan. The microRT system positioning accuracy was found to be submillimeter. The radiation source is guided through one of four catheter channels and placed in line with the tungsten collimators to deliver the conformal radiation treatment. The microRT hardware specifications, the accuracy of the treatment planning and positioning systems, and some typical procedures for radiobiological experiments that can be performed with the microRT device are presented.