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At least 1,441 records · Page 80
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DOE OSTI2016

SU-G-IeP4-14: Prostate Brachytherapy Activity Measurement and Source Localization by Using a Dual Photon Emission Computed Tomography System: A Feasibility Study

Purpose: To monitor the activity distribution and needle position during and after implantation in operating rooms. Methods: Simulation studies were conducted to assess the feasibility of measurement activity distribution and seed localization using the DuPECT system. The system consists of a LaBr3-based probe and planar detection heads, a collimation system, and a coincidence circuit. The two heads can be manipulated independently. Simplified Yb-169 brachytherapy seeds were used. A water-filled cylindrical phantom with a 40-mm diameter and 40-mm length was used to model a simplified prostate of the Asian man. Two simplified seeds were placed at a radial distance of 10 mm and tangential distance of 10 mm from the center of the phantom. The probe head was arranged perpendicular to the planar head. Results of various imaging durations were analyzed and the accuracy of the seed localization was assessed by calculating the centroid of the seed. Results: The reconstructed images indicate that the DuPECT can measure the activity distribution and locate the seeds dwelt in different positions intraoperatively. The calculated centroid on average turned out to be accurate within the pixel size of 0.5 mm. The two sources were identified when the duration is longer than 15 s. The sensitivity measured in water was merely 0.07 cps/MBq. Conclusion: Preliminary results show that the measurement of the activity distribution and seed localization are feasible using the DuPECT system intraoperatively. It indicates the DuPECT system has potential to be an approach for dose-distribution-validation. The efficacy of acvtivity distribution measurement and source localization using the DuPECT system will evaluated in more realistic phantom studies (e.g., various attenuation materials and greater number of seeds) in the future investigation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-G-TeP4-08: Automating the Verification of Patient Treatment Parameters

Purpose: To automate the daily verification of each patient’s treatment by utilizing the trajectory log files (TLs) written by the Varian TrueBeam linear accelerator while reducing the number of false positives including jaw and gantry positioning errors, that are displayed in the Treatment History tab of Varian’s Chart QA module. Methods: Small deviations in treatment parameters are difficult to detect in weekly chart checks, but may be significant in reducing delivery errors, and would be critical if detected daily. Software was developed in house to read TLs. Multiple functions were implemented within the software that allow it to operate via a GUI to analyze TLs, or as a script to run on a regular basis. In order to determine tolerance levels for the scripted analysis, 15,241 TLs from seven TrueBeams were analyzed. The maximum error of each axis for each TL was written to a CSV file and statistically analyzed to determine the tolerance for each axis accessible in the TLs to flag for manual review. The software/scripts developed were tested by varying the tolerance values to ensure veracity. After tolerances were determined, multiple weeks of manual chart checks were performed simultaneously with the automated analysis to ensure validity. Results: The tolerance values for the major axis were determined to be, 0.025 degrees for the collimator, 1.0 degree for the gantry, 0.002cm for the y-jaws, 0.01cm for the x-jaws, and 0.5MU for the MU. The automated verification of treatment parameters has been in clinical use for 4 months. During that time, no errors in machine delivery of the patient treatments were found. Conclusion: The process detailed here is a viable and effective alternative to manually checking treatment parameters during weekly chart checks.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-BRA-06: Electromagnetic Beacon Insertion in Lung Cancer Patients and Resultant Surrogacy Errors for Dynamic MLC Tumour Tracking

Purpose: To assess endo-bronchial electromagnetic beacon insertion and to quantify the geometric accuracy of using beacons as a surrogate for tumour motion in real-time multileaf collimator (MLC) tracking of lung tumours. Methods: The LIGHT SABR trial is a world-first clinical trial in which the MLC leaves move with lung tumours in real time on a standard linear accelerator. Tracking is performed based on implanted electromagnetic beacons (CalypsoTM, Varian Medical Systems, USA) as a surrogate for tumour motion. Five patients have been treated and have each had three beacons implanted endo-bronchially under fluoroscopic guidance. The centre of mass (C.O.M) has been used to adapt the MLC in real-time. The geometric error in using the beacon C.O.M as a surrogate for tumour motion was measured by measuring the tumour and beacon C.O.M in all phases of the respiratory cycle of a 4DCT. The surrogacy error was defined as the difference in beacon and tumour C.O.M relative to the reference phase (maximum exhale). Results: All five patients have had three beacons successfully implanted with no migration between simulation and end of treatment. Beacon placement relative to tumour C.O.M varied from 14 to 74 mm and in one patient spanned two lobes. Surrogacy error was measured in each patient on the simulation 4DCT and ranged from 0 to 3 mm. Surrogacy error as measured on 4DCT was subject to artefacts in mid-ventilation phases. Surrogacy error was a function of breathing phase and was typically larger at maximum inhale. Conclusion: Beacon placement and thus surrogacy error is a major component of geometric uncertainty in MLC tracking of lung tumours. Surrogacy error must be measured on each patient and incorporated into margin calculation. Reduction of surrogacy error is limited by airway anatomy, however should be taken into consideration when performing beacon insertion and planning. This research is funded by Varian Medical Systems via a collaborative research agreement.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-CAMPUS-IeP1-04: Kerma Area Product Calculation for Non-Uniform X-Ray Fields Using a Skin Dose Tracking System

Purpose: The functionality of the Dose-Tracking System (DTS) has been expanded to include the calculation of the Kerma-Area Product (KAP) for non-uniform x-ray fields such as result from the use of compensation filters during fluoroscopic procedures Methods: The DTS calculates skin dose during fluoroscopic interventions and provides a color-coded dose map on a patient-graphic model. The KAP is the integral of air kerma over the x-ray field and is usually measured with a transmission-ionization chamber that intercepts the entire x-ray beam. The DTS has been modified to determine KAP when there are beam non-uniformities that can be modeled. For example, the DTS includes models of the three compensation filters with tapered edges located in the collimator assembly of the Toshiba Infinix fluoroscopic C-Arm and can track their movement. To determine the air kerma after the filters, DTS includes transmission factors for the compensation filters as a function of kVp and beam filtration. A virtual KAP dosimeter is simulated in the DTS by an array of graphic vertices; the air kerma at each vertex is corrected by the field non-uniformity, which in this case is the attenuation factor for those rays which pass through the filter. The products of individual vertex air-kerma values for all vertices within the beam times the effective-area-per-vertex are summed for each x-ray pulse to yield the KAP per pulse and the cumulative KAP for the procedure is then calculated. Results: The KAP values estimated by DTS with the compensation filter inserted into the x-ray field agree within ± 6% with the values displayed on the fluoroscopy unit monitor, which are measured with a transmission chamber. Conclusion: The DTS can account for field non-uniformities such as result from the use of compensation filters in calculating KAP and can obviate the need for a KAP transmission ionization chamber. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-CAMPUS-JeP1-02: Proton Range Verification of Scanned Pencil Beams Using Prompt Gamma Imaging

Purpose: Prompt gammas are emitted along the proton beam path and have an emission profile correlated with the depth dose profile. In this study, the accuracy of in-vivo proton range verification using a 1-D prompt gamma camera is assessed. Methods: The 1-D camera is comprised of a tungsten slit collimator positioned in front of a linear array of LYSO scintillating crystals coupled to silicon photomultipliers. The imaged gamma profiles of individual pencil beam spots and energy layers were analyzed by determining the relative shifts from the expected gamma profiles based on analytic prediction or reference measurements. The range retrieval precision was evaluated by reproducibility measurements and by irradiation through a heterogeneous phantom composed of materials with known stopping power ratios. The camera was evaluated at clinical doses in pencil beam scanning mode on a head-and-neck phantom (HN). Two scenarios were studied: 5 mm systematic range error; and setup error of 10 mm transverse to the proton beam. Results: The camera range retrieval precision was 2 mm at clinical doses. For the heterogeneous phantom and HN phantom studies, the discrepancies between the analytic model and measurements were less than 2 mm for both spot and iso-energy layer analysis. For the simulated 5 mm range error, the retrieved shifts were 4.3±2.0 mm. For the 10 mm setup error, large shifts (> 4 mm) were observed for some spots due to differences in the irradiated and expected beam path from the measurements without setup error. Conclusion: Our studies demonstrated that in-vivo proton range verification is feasible using a 1D prompt gamma camera with a 2 mm range retrieval precision. Pencil beam spot under or over ranging can be detected via comparison between measured and expected profiles.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-CAMPUS-TeP1-03: Pre-Treatment Surface Imaging Based Collision Detection

Purpose: Modern radiotherapy increasingly employs large immobilization devices, gantry attachments, and couch rotations for treatments. All of which raise the risk of collisions between the patient and the gantry / couch. Collision detection is often achieved by manually checking each couch position in the treatment room and sometimes results in extraneous imaging if collisions are detected after image based setup has begun. In the interest of improving efficiency and avoiding extra imaging, we explore the use of a surface imaging based collision detection model. Methods: Surfaces acquired from AlignRT (VisionRT, London, UK) were transferred in wavefront format to a custom Matlab (Mathworks, Natick, MA) software package (CCHECK). Computed tomography (CT) scans acquired at the same time were sent to CCHECK in DICOM format. In CCHECK, binary maps of the surfaces were created and overlaid on the CT images based on the fixed relationship of the AlignRT and CT coordinate systems. Isocenters were added through a graphical user interface (GUI). CCHECK then compares the inputted surfaces to a model of the linear accelerator (linac) to check for collisions at defined gantry and couch positions. Note, CCHECK may be used with or without a CT. Results: The nominal surface image field of view is 650 mm × 900 mm, with variance based on patient position and size. The accuracy of collision detections is primarily based on the linac model and the surface mapping process. The current linac model and mapping process yield detection accuracies on the order of 5 mm, assuming no change in patient posture between surface acquisition and treatment. Conclusions: CCHECK provides a non-ionizing method to check for collisions without the patient in the treatment room. Collision detection accuracy may be improved with more robust linac modeling. Additional gantry attachments (e.g. conical collimators) can be easily added to the model.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-CAMPUS-TeP2-02: First Experiences and Perspectives in Using Direct Multicriteria Optimization (MCO) On Volumetric-Modulated Arc Therapy (VMAT) for Head and Neck Cancer

Purpose: To report the first experiences and perspectives in using direct multicriteria optimization (MCO) on volumetric-modulated arc therapy (VMAT) for head and neck (H&N) cancer. Methods: Ten prior patients with tumors in representative H&N regions were selected to evaluate direct MCO-VMAT in RayStation v5.0 beta. The patients were previously treated by intensity-modulated radiation therapy (IMRT) with MCO on an Elekta linear accelerator with Agility multileaf collimator. To avoid radiating eyes and shoulders, MCO-VMAT required one to three partial-arc groups, with each group consisting of single or dual arcs. All MCO-VMAT plans were approved by a radiation oncologist. The MCO-VMAT and MCO-IMRT plans were compared using V{sub 100}, D{sub 5}, homogeneity index (HI) and conformity index (CI) for planning target volume (PTV), D{sub mean} and D{sub 50} for six parallel organs and D{sub max} for five serial organs. Patient-specific quality assurance (QA) was performed using ArcCHECK for MCO-VMAT and Matrixx for MCO-IMRT with results analyzed using gamma criteria of 3%/3mm. Results: MCO-VMAT provided better V{sub 100} (+0.8%) lower D{sub 5}(− 0.3 Gy), lower HI (−0.27) and comparable CI (+0.05). MCO-VMAT decreased D{sub mean} and D{sub 50} for multiple parallel organs in seven of the ten patients. On average the reduction ranged from 2.1 (larynx) to 7.6 Gy (esophagus). For the nasal cavity and nasopharynx plans significant reduction in D{sub max} was observed for optics (up to 11 Gy) brainstem (6.4 Gy), cord (2.1 Gy) and mandible (6.7 Gy). All MCO-VMAT and -IMRT plans passed clinical QA. MCO-VMAT required slightly longer planning time due to the more complex VMAT optimization. The net beam-on time for the MCO-VMAT plans ranged from 80 to 242 seconds, up to 9 minutes shorter than MCO-IMRT. Conclusion: With similar target coverage, reduced organ dose, comparable planning time, and significantly faster treatment, MCO-VMAT is very likely to become the modality of choice in RayStation v5.0 for H&N cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

MO-FG-CAMPUS-TeP2-03: Multi-Criteria Optimization Using Taguchi Method for SRS of Multiple Lesions by Single Isocenter

Purpose: This study utilizes the Taguchi Method to evaluate the VMAT planning parameters of single isocenter treatment plans for multiple brain metastases. An optimization model based on Taguchi and utility concept is employed to optimize the planning parameters including: arc arrangement, calculation grid size, calculation model, and beam energy on multiple performance characteristics namely conformity index and dose to normal brain. Methods: Treatment plans, each with 4 metastatic brain lesions were planned using single isocenter technique. The collimator angles were optimized to avoid open areas. In this analysis four planning parameters (a–d) were considered: (a)-Arc arrangements: set1: Gantry 181cw179 couch0; gantry179ccw0, couch315; and gantry0ccw181, couch45. set2: set1 plus additional arc: Gantry 0cw179, couch270. (b)-Energy: 6-MV; 6MV-FFF (c)-Calculation grid size: 1mm; 1.5mm (d)-Calculation models: AAA; Acuros Treatment planning was performed in Varian Eclipse (ver.11.0.30). A suitable orthogonal array was selected (L8) to perform the experiments. After conducting the experiments with the combinations of planning parameters the conformity index (CI) and the normal brain dose S/N ratio for each parameter was calculated. Optimum levels for the multiple response optimizations were determined. Results: We determined that the factors most affecting the conformity index are arc arrangement and beam energy. These tests were also used to evaluate dose to normal brain. In these evaluations, the significant parameters were grid size and calculation model. Using the utility concept we determined the combination of each of the four factors tested in this study that most significantly influence quality of the resulting treatment plans: (a)-arc arrangement-set2, (b)-6MV, (c)-calc.grid 1mm, (d)-Acuros algorithm. Overall, the dominant significant influences on plan quality are (a)-arcarrangement, and (b)-beamenergy. Conclusion: Results were analyzed using ANOVA and were found to be within the confidence interval. Further investigation using this methodology. Such parameters might include: virtual OAR and optimization criterion such as normal tissue objective.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-AB-BRA-12: Quality Assurance of An Integrated Magnetic Resonance Image Guided Adaptive Radiotherapy Machine Using Cherenkov Imaging

Purpose: To investigate the viability of using Cherenkov imaging as a fast and robust method for quality assurance tests in the presence of a magnetic field, where other instruments can be limited. Methods: Water tank measurements were acquired from a clinically utilized adaptive magnetic resonance image guided radiation therapy (MR-IGRT) machine with three multileaf-collimator equipped 60Co sources. Cherenkov imaging used an intensified charge coupled device (ICCD) camera placed 3.5m from the treatment isocenter, looking down the bore of the 0.35T MRI into a water tank. Images were post-processed to make quantitative comparison between Cherenkov light intensity with both film and treatment planning system predictions, in terms of percent depth dose curves as well as lateral beam profile measurements. A TG-119 commissioning test plan (C4: C-Shape) was imaged in real-time at 6.33 frames per second to investigate the temporal and spatial resolution of the Cherenkov imaging technique. Results: A .33mm/pixel Cherenkov image resolution was achieved across 1024×1024 pixels in this setup. Analysis of the Cherenkov image of a 10.5×10.5cm treatment beam in the water tank successfully measured the beam width at the depth of maximum dose within 1.2% of the film measurement at the same point. The percent depth dose curve for the same beam was on average within 2% of ionization chamber measurements for corresponding depths between 3–100mm. Cherenkov video of the TG-119 test plan provided qualitative agreement with the treatment planning system dose predictions, and a novel temporal verification of the treatment. Conclusions: Cherenkov imaging was successfully used to make QA measurements of percent depth dose curves and cross beam profiles of MRI-IGRT radiotherapy machines after only several seconds of beam-on time and data capture; both curves were extracted from the same data set. Video-rate imaging of a dynamic treatment plan provided new information regarding temporal dose deposition. This study has been funded by NIH grants R21EB17559 and R01CA109558, as well as Norris Cotton Cancer Center Pilot funding.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-FG-201-04: Computer Vision in Autonomous Quality Assurance of Linear Accelerators

Purpose: Routine quality assurance (QA) of linear accelerators represents a critical and costly element of a radiation oncology center. Recently, a system was developed to autonomously perform routine quality assurance on linear accelerators. The purpose of this work is to extend this system and contribute computer vision techniques for obtaining quantitative measurements for a monthly multi-leaf collimator (MLC) QA test specified by TG-142, namely leaf position accuracy, and demonstrate extensibility for additional routines. Methods: Grayscale images of a picket fence delivery on a radioluminescent phosphor coated phantom are captured using a CMOS camera. Collected images are processed to correct for camera distortions, rotation and alignment, reduce noise, and enhance contrast. The location of each MLC leaf is determined through logistic fitting and a priori modeling based on knowledge of the delivered beams. Using the data collected and the criteria from TG-142, a decision is made on whether or not the leaf position accuracy of the MLC passes or fails. Results: The locations of all MLC leaf edges are found for three different picket fence images in a picket fence routine to 0.1mm/1pixel precision. The program to correct for image alignment and determination of leaf positions requires a runtime of 21– 25 seconds for a single picket, and 44 – 46 seconds for a group of three pickets on a standard workstation CPU, 2.2 GHz Intel Core i7. Conclusion: MLC leaf edges were successfully found using techniques in computer vision. With the addition of computer vision techniques to the previously described autonomous QA system, the system is able to quickly perform complete QA routines with minimal human contribution.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-FG-BRB-06: A Prompt Gamma-Ray Spectroscopy System for Clinical Studies of in Vivo Proton Range Verification

Purpose: We present a new system to perform prompt gamma-ray spectroscopy during proton pencil-beam scanning treatments, which enables in vivo verification of the proton range. This system will be used for the first clinical studies of this technology. Methods: After successful pre-clinical testing of prompt gamma-ray spectroscopy, a full scale system for clinical studies is now being assembled. Prompt gamma-rays will be detected during patient treatment using an array of 8 detector modules arranged behind a tungsten collimator. Each detector module consists of a lanthanum(III) bromide scintillator, a photomultiplier tube, and custom electronics for stable high voltage supply and signal amplification. A new real-time data acquisition and control system samples the signals from the detectors with analog-to-digital converters, analyses events of interest, and communicates with the beam delivery systems. The timing of the detected events was synchronized to the cyclotron radiofrequency and the pencil-beam delivery. Range verification is performed by matching measured energy- and timeresolved gamma-ray spectra to nuclear reaction models based on the clinical treatment plan. Experiments in phantoms were performed using clinical beams in order to assess the performance of the systems. Results: The experiments showed reliable real-time analysis of more than 10 million detector events per second. The individual detector modules acquired accurate energy- and time-resolved gamma-ray measurements at a rate of 1 million events per second, which is typical for beams delivered with a clinical dose rate. The data acquisition system successfully tracked the delivery of the scanned pencil-beams to determine the location of range deviations within the treatment field. Conclusion: A clinical system for proton range verification using prompt gamma-ray spectroscopy has been designed and is being prepared for use during patient treatments. We anticipate to start a first clinical study in the near future. This work was supported by the Federal Share of program income earned by Massachusetts; General Hospital on C06-CA059267, Proton Therapy Research and Treatment Center.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-FG-BRB-11: Design and Evaluation of a Robotic C-Arm CBCT System for Image-Guided Proton Therapy

Purpose: To describe the design and performance of a ceiling-mounted robotic C-arm CBCT system for image-guided proton therapy. Methods: Uniquely different from traditional C-arm CBCT used in interventional radiology, the imaging system was designed to provide volumetric image guidance for patients treated on a 190-degree proton gantry system and a 6 degree-of-freedom (DOF) robotic patient positioner. The mounting of robotic arms to the ceiling rails, rather than gantry or nozzle, provides the flexibility in imaging locations (isocenter, iso+27cm in X, iso+100cm in Y) in the room and easier upgrade as technology advances. A kV X-ray tube and a 43×43cm flat panel imager were mounted to a rotating C-ring (87cm diameter), which is coupled to the C-arm concentrically. Both C-arm and the robotic arm remain stationary during imaging to maintain high position accuracy. Source-to-axis distance and source-to-imager distance are 100 and 150cm, respectively. A 14:1 focused anti-scatter grid and a bowtie filer are used for image acquisition. A unique automatic collimator device of 4 independent blades for adjusting field of view and reducing patient dose has also been developed. Results: Sub-millimeter position accuracy and repeatability of the robotic C-arm were measured with a laser tracker. High quality CBCT images for positioning can be acquired with a weighted CTDI of 3.6mGy (head in 200° full fan mode: 100kV, 20mA, 20ms, 10fps)-8.7 mGy (pelvis in 360° half fan mode: 125kV, 42mA, 20ms, 10fps). Image guidance accuracy achieved <1mm (3D vector) with automatic 3D-3D registration for anthropomorphic head and pelvis phantoms. Since November 2015, 22 proton therapy patients have undergone daily CBCT imaging for 6 DOF positioning. Conclusion: Decoupled from gantry and nozzle, this CBCT system provides a unique solution for volumetric image guidance with half/partial proton gantry systems. We demonstrated that daily CBCT can be integrated into proton therapy for pre-treatment position verification.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-H-BRA-08: The Design and Characteristics of a Novel Compact Linac-Based MRI Guided Radiation Therapy (MR-IGRT) System

Purpose: To describe the design and characteristics of a novel linac-based MRI guided radiation therapy system that addresses RF and magnetic field interference and that can be housed in conventional radiotherapy vaults. Methods: The MR-IGRT system will provide simultaneous MR imaging combined with both simple (3D) and complex (IMRT, SBRT, SRS) techniques. The system is a combination of a) double-donut split solenoidal superconducting 0.345T MRI; and b) a 90 cm isocenter ring-gantry mounted 6MV, flattening filter-free linac coupled with a stacked doubly-focused multileaf collimator with 4 mm resolution. A novel RF shielding and absorption technology was developed to isolate the beam generating RF emissions from the MR, while a novel magnetic shielding sleeve system was developed to place the magnetic field-sensitive components in low-magnetic field regions. The system design produces high spatial resolution radiation beams with state-of-the art radiation dose characteristics and simultaneous MR imaging. Results: Prototype testing with a spectrum analyzer has demonstrated complete elimination of linac RF inside the treatment room. The magnetic field inside of the magnetic shielding was well below the specification, allowing the linear accelerator to operate normally. A novel on-gantry shimming system maintained < 25 ppm magnetic field homogeneity over a 45 cm spherical field of view for all gantry angles. Conclusion: The system design demonstrates the feasibility coupling a state-of-the art linac system with a 0.345T MRI, enabling highly conformal radiation therapy with simultaneous MR image guidance. S. Mutic’s employer (Washington University) has grant with ViewRay; D. Low is former ViewRay scientific advisory board member (ended October 2015); T. Chmielewski, G. Fought, M. Hernandez, I. Kawrakow, A. Sharma, S. Shvartsman, J. Dempsey are employees of ViewRay with stock options (Dempsey has leadership role and Dempsey/Kawrakow have stock).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-H-207A-02: Relative Importance of the Various Factors Influencing the Accuracy of Monte Carlo Simulated CT Dose Index

Purpose: Monte Carlo simulation is a frequently used technique for assessing patient dose in CT. The accuracy of a Monte Carlo program is often validated using the standard CT dose index (CTDI) phantoms by comparing simulated and measured CTDI{sub 100}. To achieve good agreement, many input parameters in the simulation (e.g., energy spectrum and effective beam width) need to be determined. However, not all the parameters have equal importance. Our aim was to assess the relative importance of the various factors that influence the accuracy of simulated CTDI{sub 100}. Methods: A Monte Carlo program previously validated for a clinical CT system was used to simulate CTDI{sub 100}. For the standard CTDI phantoms (32 and 16 cm in diameter), CTDI{sub 100} values from central and four peripheral locations at 70 and 120 kVp were first simulated using a set of reference input parameter values (treated as the truth). To emulate the situation in which the input parameter values used by the researcher may deviate from the truth, additional simulations were performed in which intentional errors were introduced into the input parameters, the effects of which on simulated CTDI{sub 100} were analyzed. Results: At 38.4-mm collimation, errors in effective beam width up to 5.0 mm showed negligible effects on simulated CTDI{sub 100} (<1.0%). Likewise, errors in acrylic density of up to 0.01 g/cm{sup 3} resulted in small CTDI{sub 100} errors (<2.5%). In contrast, errors in spectral HVL produced more significant effects: slight deviations (±0.2 mm Al) produced errors up to 4.4%, whereas more extreme deviations (±1.4 mm Al) produced errors as high as 25.9%. Lastly, ignoring the CT table introduced errors up to 13.9%. Conclusion: Monte Carlo simulated CTDI{sub 100} is insensitive to errors in effective beam width and acrylic density. However, they are sensitive to errors in spectral HVL. To obtain accurate results, the CT table should not be ignored. This work was supported by a Faculty Research and Development Award from Cleveland State University.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-H-207A-03: CT Hounsfield Unit Accuracy: Effect of Beam Hardening On Phantom and Clinical Whole-Body CT Images

Purpose: To assess the effect of beam hardening on measured CT HU values. Methods: An anthropomorphic knee phantom was scanned with the CT component of a GE Discovery 690 PET/CT scanner (120kVp, 300mAs, 40?0.625mm collimation, pitch=0.984, FOV=500mm, matrix=512?512) with four different scan setups, each of which induces different degrees of beam hardening by introducing additional attenuation media into the field of view. Homogeneous voxels representing “soft tissue” and “bone” were segmented by HU thresholding followed by a 3D morphological erosion operation which removes the non-homogenous voxels located on the interface of thresholded tissue mask. HU values of segmented “soft tissue” and “bone” were compared.Additionally, whole-body CT data with coverage from the skull apex to the end of toes were retrospectively retrieved from seven PET/CT exams to evaluate the effect of beam hardening in vivo. Homogeneous bone voxels were segmented with the same method previously described. Total In-Slice Attenuation (TISA) for each CT slice, defined as the summation of HU values over all voxels within a CT slice, was calculated for all slices of the seven whole-body CT datasets and evaluated against the mean HU values of homogeneous bone voxels within that slice. Results: HU values measured from the phantom showed that while “soft tissue” HU values were unaffected, added attenuation within the FOV caused noticeable decreases in the measured HU values of “bone” voxels. A linear relationship was observed between bone HU and TISA for slices of the torso and legs, but not of the skull. Conclusion: Beam hardening effect is not an issue of concern for voxels with HU in the soft tissue range, but should not be neglected for bone voxels. A linear relationship exists between bone HU and the associated TISA in non-skull CT slices, which can be exploited to develop a correction strategy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TU-H-CAMPUS-IeP1-02: Validation of a CT Monte Carlo Software

Purpose: To validate the in-house developed CT Monte Carlo calculation tool GMctdospp against reference simulation sets provided by the AAPM in the new report 195. Methods: Deposited energy was calculated in four segments (test 1) and two 10 cm long cylinders (test 2) inside a CTDI phantom (following case #4 of the AAPM report 195). The x-ray point source of a given 120 kVp spectrum was collimated to a fan beam with two thicknesses (10 mm, 80 mm) for a static and a rotational setup. In addition, a given chest geometry was used to calculate deposited energy in several organs for a 0° static and a rotational beam (following case #5 of the AAPM report 195). The results of GMctdospp were compared against the particular mean value of the four quoted Monte Carlo codes (EGSnrc, Geant 4, MCNP and Penelope). Results: Calculated values showed no outliers in any of the cases. Differences between GMctdospp and the particular mean Results: Calculated values showed no outliers in any of the cases. Differences between GMctdospp and the particular mean value were always at similar magnitude compared to the quoted codes. For case #4 (CTDI phantom) the relative differences were within 1.5 %, on average 0.4 % and for case #5 (chest phantom) within 2.5 % and on average 0.85 %. Conclusion: The results confirmed an overall uncertainty of the Monte-Carlo calculation chain in GMctdospp being <2.5 %, for most cases even better. This can be considered small compared to other sources of uncertainties, e.g. virtual source and patient models. The photon transport implemented in GMctdospp inside a voxel-based patient geometry was successfully verified.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-DE-BRA-11: A Study of Motion Tracking Accuracy of Robotic Radiosurgery Using a Novel CCD Camera Based End-To-End Test System

Purpose: A novel end-to-end test system using a CCD camera and a scintillator based phantom (XRV-124, Logos Systems Int’l) capable of measuring the beam-by-beam delivery accuracy of Robotic Radiosurgery (CyberKnife) was developed and reported in our previous work. This work investigates its application in assessing the motion tracking (Synchrony) accuracy for CyberKnife. Methods: A QA plan with Anterior and Lateral beams (with 4 different collimator sizes) was created (Multiplan v5.3) for the XRV-124 phantom. The phantom was placed on a motion platform (superior and inferior movement), and the plans were delivered on the CyberKnife M6 system using four motion patterns: static, Sine- wave, Sine with 15° phase shift, and a patient breathing pattern composed of 2cm maximum motion with 4 second breathing cycle. Under integral recording mode, the time-averaged beam vectors (X, Y, Z) were measured by the phantom and compared with static delivery. In dynamic recording mode, the beam spots were recorded at a rate of 10 frames/second. The beam vector deviation from average position was evaluated against the various breathing patterns. Results: The average beam position of the six deliveries with no motion and three deliveries with Synchrony tracking on ideal motion (sinewave without phase shift) all agree within −0.03±0.00 mm, 0.10±0.04, and 0.04±0.03 in the X, Y, and X directions. Radiation beam width (FWHM) variations are within ±0.03 mm. Dynamic video record showed submillimeter tracking stability for both regular and irregular breathing pattern; however the tracking error up to 3.5 mm was observed when a 15 degree phase shift was introduced. Conclusion: The XRV-124 system is able to provide 3D and 4D targeting accuracy for CyberKnife delivery with Synchrony. The experimental results showed sub-millimeter delivery in phantom with excellent correlation in target to breathing motion. The accuracy was degraded when irregular motion and phase shift was introduced.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TH-AB-201-05: Determining the Direction Distribution of the Primary Radiation for a Cyberknife-M6

Purpose: Radiation protection regulatory differentiates between primary and scatter radiation. Whereas for conventional clinical linear accelerators the solid angle for primary radiation is planar, the Cyberknife (Accuray Inc., Sunnyvale, CA) may point its beam in all spatial directions. In order to be able to judge on radiation protection calculations for a Cyberknife-M6 vault, the direction distribution for delivered plans was evaluated based on clinical experiences. Methods: The log-files of 121 delivered patient treatment plans were exported, divided into cranial and extra-cranial treatments and the delivered monitor units (MU) together with the corresponding beam directions were analyzed. This MU-weighted spatial distribution was then projected to a 9.5 × 5.9 × 3.9 m{sup 3} vault, generating an “intensity map” using a binning of 50 × 50 cm{sup 2}. The factor of direction (FOD) is reported as a fraction of the total applied MUs to the walls, ceiling and floor in the perspective of a patient lying in head-first-supine position on the couch. In this study, the term intFOD refers to the integral FOD and maxFOD refers to the maximal FOD for a single bin. Results: For all kind of treatments and collimators, intFOD and maxFOD for the wall behind the patient’s head is 0.0. The intFOD for the floor varies between 0.65 and 0.74. For the ceiling, maxFOD is 0.002 and 0.0 for cranial and extra-cranial cases, respectively. The intFOD for the wall at the patient’s feet, is 0.094 for cranial and 0.005 for extra-cranial cases. There is nearly no difference between the maxFOD of the right and left wall for cranial cases, whereas for extra-cranial cases these numbers differ by a factor of 1.75. Conclusion: The varying FODs for the Cyberknife were quantified based on delivered treatment plans. These findings are helpful regarding the design of Cyberknife vaults.

60 APPLIED LIFE SCIENCES↗