bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐D‐211‐04: Sector Intensity Modulated (SIM) Gamma Knife Stereotactic Radiosurgery
Authors: Nie K , Pouliot J , Hwang A , Sneed P , McDermott M , Ma L
Published: June 2012

Purpose: The latest Gamma Knife (GK) system, Perfexion, consists of 192 Co‐60 sources divided into eight sectors. Treatment delivery includes multiple shots placed at different positions. For every shot, each sector can be either blocked or open with four different aperture sizes. However, the beam‐on time is designed to be fixed. We proposed an innovative concept, Sector Intensity Modulated (SIM) Gamma Knife by dynamically varying the beam‐on time for each individual sector to improve stereotactic radiosurgery planning quality. Methods: The anatomic structures and dose matrices from each sector for every shot were obtained from the GK workstation. The beam‐on time for each sector was decomposed with various discrete levels and brute‐force algorithm was used to get the optimal solution. The resulting SIM plan was then re‐entered into the GK workstation. Six indices were used to benchmark the plan quality: Coverage, Conformality, Gradient, Maximum Dose(s) to critical structure(s), Volume receiving over 8 and 12 Gy. All the SIM plans in comparison with the original plans were further reviewed by an experienced oncologist. Results: The simulations were tested on various pituitary adenoma cases. Results consistently showed that SIM yielded better plans with all quantitative indices improved compared to original plan. It provides better conformality, quicker drop off of the isodose line outside the tumor, lower doses to the critical structures as optical‐ nerve/chiasm while maintaining at least 99% coverage of the tumor. Results were more favorable according to oncologist's view. In particular, up to 20% or 0.6 cc volume decrease in healthy tissue receiving 8 Gy was observed. This may translate into clinically observable reduction in acute/late toxicities. Conclusions: Our preliminary results show that Sector Intensity Modulated Gamma Knife offers superior treatment plans compared to the originally delivered plans. Further works as adding dynamic shot location and dynamic shot shaping will be discussed.
SU‐D‐211‐05: A Systematic Analysis of Penumbra Characteristics in Conformai Arc Delivery for SBRT and Its Utilization for Negative Margin Technique (NMT), a Novel Planning Strategy for Improving Dose Conformation
Authors: Kim S , Serago C , Smith A
Published: June 2012

Purpose: To systematically analyze penumbra characteristics in co‐planar arc‐beams and demonstrate how optimal aperture margin (OAM) can be systematically estimated. Methods: Full arc‐beam delivery was simulated with a Pinnacle RTP for a total of 32 cases. Considered factors were energy (6X, 6F, 10X, and 10F, where ‘F’ indicates flattening‐filter‐free), field‐size (2×2, 4×4, 6×6, and 8×8), and two materials (50×50×50 cm×cm×cm water and 50×50×50 cmxcmxcm water with a 20 cm diameter sphere of 0.25 g/cc lung density at the center). The highest‐dose‐gradient (HDG) and its range in both radial‐dose‐distribution (RDD) and longitudinal‐dose‐distribution (LDD) were evaluated. For OAM estimation, start with simulated dose distributions in interest. Measure coverage size (CS) at the chosen PIL in the RDD. The difference between the target size (TS) and the CS is the margin needed. In radial‐direction, choose a PIL where the CS is larger than the TS [resulting in ‘negative margin (NM)’] to enhance conformation capability.Next, measure the CS at the chosen PIL in the LDD. Longitudinally, positive margin is expected in general. This process was applied to 6X and 10F cases in lung to illustrate its applicability. Results: Overall, larger HDG was observed in 6 MV (than 10 MV), smaller fields, LDD (than RDD), and in water (than lung). 6F showed slightly larger HDG than 6X while 10X did than 10F. Dose fall‐off started significantly farther from the CAX in RDD than LDD, supporting the NM concept. With the systematic margin estimation applied, expected PILs matched closely with isodose points having tight target coverage, indicating the applicability of the method. Conclusions: Among tested, the 6F beam provides the most optimal dose distribution for dose conformation. The range of optimal PIL decreases as field‐size increases. It has been demonstrated optimal AMs can be systematically estimated as proposed in this study.
SU‐D‐211‐06: The Effect of Motion in RapidArc Lung SBRT Delivery
Authors: Zou J , Yin L , Shen J , Corradetti M , Kirk M , Rengan R , Teo B. K.
Published: June 2012

Purpose: RapidArc is routinely used for stereotactic radiotherapy for lung cancer. While treatment dose is optimized and calculated on a static CT image, the motion of the target in conjunction with the motion of the MLC may Result in a delivered dose deviating from the planed dose. In this study, we investigate the dosimetric consequences of the inter‐play effect by simulating dynamic dose delivery on a dynamic CT dataset of real patients. Methods: The target motion in 20 patients was analyzed and 5 patients with >10 mm motion were chosen for this study. The RapidArc plan for eachpatient is optimized on a free‐breathing CT using 2 arcs. Inherent in each plan is data on the associated parameters such as timestamp, MLC leave position, gantry angle and delivered beam MUs for each control point. Simulated dynamic delivery is performed by associating these parameters with each of the breathing phases of the 4D‐CT. The starting breathing phase is selected randomly for each of the two arcs. Dose from the derived partial plans associated with each phase of the 4D‐CT dose is recalculated in Eclipse. Accumulation of dose is performed using deformable image registration from each phase of the 4D‐CT to the exhale phase of the 4D‐CT. Results: The coverage of the GTV and PTV shows negligible variations from the interplay effect. But the Homogeneity Index is affected by the motion. The prescription isodose volume is smaller than what was from the treatment plan dose. There were both intra‐ and inter‐fraction effects seen inthe OARs dose in some patients. Conclusions: We investigated the motioneffect in RapidArc Lung SBRT delivery in 5 patients. Negligible variations were shown for target coverage. However the motion effects were observed in high dose distribution and volume. Some OARs dose distributions were affected by the motion.
SU‐D‐213AB‐02: Optimal Design of Multichannel Vaginal Cylinder Applicators for High Dose Rate Brachytherapy
Authors: Park S , Demanes J , Kamrava M
Published: June 2012

Purpose: To determine the optimal location of catheters in multichannel vaginal applicators to appropriately cover the vaginal cuff target and minimize dose to the organs at risk (OARs) and hot spots in the target. Methods: A new multichannel vaginal applicator with a diameter of 30 mmconsists of a single central catheter and an outer array of eight catheters. A total of 20 plans were generated from 5 patients by using different outer catheter locations at r = 4, 8, and 12 mm. The target was defined as a 5 mmcircumferential shell extending 4 cm in length around the applicator, excluding the bladder, rectum, and bowel. An inverse planning simulated annealing algorithm and graphical optimization was applied to ensure the prescription dose (7.0 Gy per fraction) covered >97% of the target and minimized dose to the OARs. Target coverage (D90 and V100), hot spots (V150 and V200), and OAR doses (D0.1cc, D1cc, and D2cc) from the various catheter placements were compared to single catheter plans. Results: By study design all plans had the same target coverage D90 (105.0– 108.3%) and V100 (97.1–97.2%). The V150 and V200 were 16.1% and 3.4% (r=0mm), 17.3% and 4.2% (r=4mm), 20.1% and 2.2% (r=8mm), and 30.1% and 6.0% (r=12mm). The DO.1cc to the OARs from the various catheter placements at r = 4, 8, and 12 mm was reduced by 4.0%, 8.6%, 11.9% (bladder), 7.4%, 13.2%, and 17.4% (rectum), when compared to the central catheter plans. Conclusions: Multichannel vaginal applicators provide better dosimetry than single channel applicator. The catheter array located closest to the applicator surface most significantly reduces dose tothe OARs at the expense of larger hot spots in the target. The array in the middle of the applicator radius provides significantly decreased dose to the OARs and gave relatively smaller hot spots.
SU‐D‐213AB‐04: Evaluation of the Dose Calculation in a Commercial Planning System for a Breast Cancer Brachytherapy Technology Using Monte Carlo Simulation
Authors: Graf M , Cervino L , Scanderbeg D , Yashar C , Jiang S
Published: June 2012

Purpose: To evaluate the dose calculation in a commercial treatment planning system (TPS) for a breast cancer brachytherapy technology using Monte Carlo simulation for 21 patients. Methods: Plans for 21 patients who received SAVI treatments were modeled using data from the TPS including CT images, structures and source information. The MC code PENELOPE was used, inputting images in voxel format, where density and material (tissue, air, bone and Nitinol) for each voxel were assigned based on its calibrated Hounsfield units and contoured structure sets, respectively. For the source model only gamma‐rays and fluorescence X‐rays of the NuDat database 192Ir spectrum were used, leaving out photons with emission intensity less than 0.1% and X‐rays with energies below 10 keV. Source positions were entered into the plan and run individually. Dose was totaledby individually weighting the dose for each source position using the original TPS plan dwell times and then summing the weighted dose for all positions. Results: Dose from the Monte Carlo plan was compared with dose from the original plan using isodose lines at 50, 100, 150 and 200% of the prescription dose of 34Gy. Dosimetric coverage of the target was compared by evaluating the V100, V150 and V200 (volume of the target covered by 100%, 150 and 200% of the dose respectively). The V200 and V150 had an average increase (and standard deviation) of 9.1% (3.2%) and 3.8% (1.4%) respectively, while the average change in V100 was 1.2% (1.0%). Where variance for the entire simulation was 0.9%. Conclusion: We have compared dose distributions of a commercial TPS using Monte Carlo simulation for SAVI breast cancer brachytherapy and found that a dose increase near the air‐tissue interface.
SU‐D‐BRB‐01: 4D‐CT Lung Ventilation Images Vary with 4D‐CT Sorting Techniques
Authors: Yamamoto T , Kabus S , Lorenz C , Johnston E , Maxim P , Loo B , Keall P
Published: June 2012

Purpose: 4D‐CT ventilation imaging is a novel promising technique for lung functional imaging and has potential as a biomarker for radiation pneumonitis, but has not been validated in human subjects. The current 4D‐ CT technique with phase‐based sorting results in artifacts at an alarmingly high frequency (90%), which may introduce variations into ventilation calculations. The purpose of this study was to quantify the variability of 4D‐ CT ventilation imaging to 4D‐CT sorting techniques. Methods: Two 4D‐CT images were generated from the same data set by: (1) phase‐based; (2) anatomic similarity‐ and abdominal displacement‐based sorting for five patients. Two ventilation image sets (V_phase and V_anat) were then calculated by deformable image registration of peak‐exhale and peak‐inhale4D‐CT images and quantification of regional volume change based on Hounsfield unit change. The variability of 4D‐CT ventilation imaging wasquantified using the voxel‐based Spearman rank correlation coefficients and Dice similarity coefficients (DSC) for the spatial overlap of segmented low‐ functional lung regions. The relationship between the abdominal motionrange variation and ventilation variation was also assessed using linearregression. Furthermore, the correlations between V_phase or V_anat and SPECT ventilation images (assumed ground‐truth) were compared. Results: In general, displacement‐ and anatomic similarity‐based sorting reduced 4D‐ CT artifacts compared to phase‐based sorting. The voxel‐based correlationsbetween V_phase and V_anat were only moderate (range, 0.57–0.77). The DSCs for the low‐functional lung regions were moderate to substantial (0.58–0.70). The relationship between the motion range variation and ventilation variation was strong on average (R2=0.79±0.25), suggesting that ventilation variations are related to 4D‐CT artifacts. Vanat was found to improve correlations with SPECT ventilation images compared to V_phase.Conclusions: 4D‐CT ventilation images vary markedly with 4D‐CT sorting techniques. 4D‐CT artifacts should be considered as a significant source of variation in 4D‐CT ventilation imaging during its validation. This study wassupported in part by NIH/NCI R01 93626. SK and CL are employees ofPhilips Research.
SU‐D‐BRA‐02: An Extended Time‐Variant Seasonal Autoregressive Model‐Based Prediction for Irregular Breathing Motion Tracking
Authors: Ichiji K , Homma N , Sakai M , Narita Y , Takai Y , Yoshizawa M
Published: June 2012

Purpose: Real‐time tumor position/shape measurement and dynamic beam tracking techniques allow accurate and continuous irradiation to moving tumor, but there can be a delay of several hundred milliseconds between observation and irradiation. A time‐variant seasonal autoregressive (TVSAR) model has been proposed for compensating the delay by predicting respiratory tumor motion with sub‐millimeter accuracy for a second latency. This is the‐state‐of‐the‐art model for almost regular breathing prediction so far. In this study, we propose an extended prediction method based on TVSAR to be usable for various breathing patterns, by predicting the residual component obtained from conventional TVSAR. Methods: An essential core of the method is to take into account the residual component that is not predictable by only TVSAR. The residual component involves baseline shift, amplitude variation, and so on. In this study, the time series of the residual obtained for every new sample are predicted by using autoregressive (AR) model. The order and parameters of the AR model is adaptively determined for each residual component by using an information criterion. Eleven data sets of 3‐D lung tumor motion, observed at Georgetown University Hospital by using Cyberknife Synchrony system, were used for evaluation of the prediction performance. Results: Experimental results indicated that the proposed method is superior to those of conventional and the state‐of‐the‐art methods for 0 to 1 s ahead prediction. The average prediction error of the proposed method was 0.920 plus/minus 0.348 mm for 0.5 s forward prediction. Conclusion: We have developed the new prediction method based on TVSAR model with adaptive residual prediction. The new method can predict various respiratory motions including not only regular but also a variety of irregular breathing patterns and thus can compensate the bad effect of the delay in dynamic irradiation system for moving tumor tracking. A part of this work has been financially supported by Varian Medical Systems Inc., Palo Alto, CA and Japan Society for the Promotion of Science (JSPS), Japan.
SU‐D‐BRA‐05: Prostatectomy Patient's Bladder and Rectum Inter‐Fraction Organ Motion and Deformation Can Be Described by a Gaussian Signed Distance Field
Authors: Hu E , Zhou S
Published: June 2012

Purpose: The inter‐fraction organ motion/deformation can be conveniently modeled using Bayesian theory with Normal‐gamma conjugate prior if signed distance from any fixed point in space to surface of the organ of interest obeys normal distribution. In this study, we investigated whether the inter‐fraction motion/deformation of bladder and rectum observed from clinical prostatectomy patients satisfy this normality condition. Method and Materials: 285 treatment planning CT and daily CT‐on‐rails scans from 7 prostatectomy patients were used in this study. Both bladder and rectum were contoured on all scans. Each patient's daily CT‐on‐rails scans were registered to his treatment planning CT and the bladder/rectum contours were mapped into treatment planning CT space for analysis. A cubic box with orientations along treatment planning CT image axes is defined to contain all bladders/rectums with 2cm margin. For each voxel inside this box (size: 2mm×2mm×1.5mm), its distance to the bladder/rectum surfaces was measured. Sign is added to the distance to indicate whether a point is inside or outside of an organ of interest. Now the inter‐fraction motion/deformation of bladder/rectum can be characterized by the distance variation from the voxels to the bladder/rectum surface. Jarque‐Bera normality statistical test was employed to examine whether the signed distances obey normal distribution. Results: For each patient, the signed distance to bladder or rectum from at least 99.99% of the voxels passed the Jarque‐Bera test with p‐value 0.05. Conclusions: For prostatectomy patients, their bladder or rectum inter‐fraction organ motion/deformation can be statistically described by a Gaussian signed distance field. This makes it possible to use Bayesian statistics model with Normal‐gamma conjugate prior to predict bladder or rectum daily location and shape during a prostatectomy patient fractionated radiotherapy.
SU‐D‐213CD‐06: Workflow and Safety Systems of a Linac‐MR Sim‐Brachytherapy MRgRT™ Facility
Authors: Winter J , Carlone M , Stanescu T , Breen S , Foxcroft S , Guyot B , Dahan M , Dahdal R , Jaffray D
Published: June 2012

Purpose: To develop the operational workflow and safety systems of a magnetic resonance‐guided radiotherapy system (MRgRT™), which comprises an MR scanner on rails that travels between a linac vault, MR simulation room and brachytherapy suite. Methods: To develop a safe and streamlined clinical workflow, we conducted a comprehensive process review based on a layered approach to overall MRgRT safety that included i) facility design, (ii) workflow iii) system design and interlocks and iv) policies and procedures. We applied existing guidelines for MR and radiation safety, and employed system‐level failure modes and effects analyses to design the MRgRT facility and clinical procedures. Results: In the MRgRT system configuration, the MR and treatment systems are physically decoupled and used independently requiring novel administration of existing MR and radiation guidelines. A key element for the safe operation of the moving MR unit is the concept that all three rooms represent zone 4 areas (American College of Radiology guidelines). Using this concept, we applied MR guidelines to develop safe procedures for the overall suite, including screening of all persons entering the suite in zone 2 and control of ferromagnetic materials. We generated a clinical workflow that ensures expedient and safe transition between MR imaging and treatment delivery in both the linac and brachytherapy rooms. In addition, we designed emergency protocols for MRgRT, which helped drive requirements for the facility and system design, e.g., need for an accessible MR‐safe stretcher. Conclusions: We designed the first comprehensive description of the MRgRT workflow, interlocking systems and safety procedures. With this layered approach to safety, we addressed critical aspects regarding safe operation and workflow for the system and provided multiple redundancies for key processes. Coupled with customized staff training, the proposed design ensures the safe operation of the MRgRT facility. This work has received research personnel support from IMRIS.
SU‐D‐217BCD‐02: Online Angular Tube Current Modulation in X‐Ray Computed Tomography: Can Tube Current Be Modulated Appropriately?
Authors: Matsubara K , Koshida H , Takata T , Horii J , Iida H , Koshida K , Matsui O , Fukuda A
Published: June 2012

Purpose: In X‐ray computed tomography (CT), X‐rays are significantly less attenuated in the anteroposterior direction and more in the lateral direction. Therefore, the tube current should be adjusted within one gantry rotation using angular tube current modulation (TCM). The aim of this study was to evaluate whether online angular TCM could reduce radiation dose appropriately. Methods: A 128‐detector dual‐source CT (SOMATOM Definition Flash; Siemens Healthcare, Erlangen, Germany) and an online TCM system (CARE Dose 4D; Siemens Healthcare) were used. Dose profiles were acquired using the CT Dose Profiler (RTI Electronics, Molndal, Sweden) and an elliptical cylindrical phantom (MHT; Kyoto Kagaku, Kyoto, Japan) for helical CT scans with and without TCM. In addition, absorbed dose distributions within a single section were acquired using an anthropomorphic phantom (RANI 10; The Phantom Laboratory, Salem, NY) and radiophotoluminescent glass dosimeters (RPLDs) (GD‐ 302M; Chiyoda Technol, Tokyo, Japan) for helical CT scans with and without TCM after placing RPLDs within all holes of one section and pasting them around the section. A graph of each absorbed dose distribution was drawn using graphing software (ORIGIN 8.6; OriginLab, Northampton, MA). Results: The acquired dose profiles suggested that online angular TCM could adjust the tube current in near‐real time according to the attenuation measured from the previous projection. The profiles gradually stabilized because the tube current was adjusted properly. The absorbed doses were low and the distributions were stable with TCM compared with those without TCM. Conclusions: In X‐ray CT, an online angular TCM can reduce radiation dose effectively by adjusting tube current within one gantry rotation in near‐real time.
SU‐D‐217BCD‐04: How Do We Know How Low Can We Go in Lung Cancer Screening CT?
Authors: Chen L , Sykes A , Jensen E , Eiken P , Yu L , Leng S , McCollough C
Published: June 2012

Purpose: To demonstrate a technique for determining the acceptable radiation dose level for lung cancer screening CT. Methods: 20 patients who underwent a clinically indicated routine chest CT scan with 120 kV and 180 quality reference mAs were enrolled in this IRB approved study. Automatic exposure control was used to adjust for patient size. Scanner output, as expressed in CTDIvol, varied accordingly (mean=16.8 mGy, range=7.6 to 26.6 mGy). A previously validated noise insertion software tool developed in our lab was used to simulate scans acquired with reduced dose levels (12.5%, 25%, 50% of the original dose level). Images reconstructed from the same raw data but at the original and simulated, reduced dose levels were randomized and blindly reviewed by three thoracic radiologists. Lung and soft tissue regions were graded for two different imaging tasks: 1) routine diagnostic CT exam of the chest and 2) screening exam of the chest for lung cancer. A 5 point scale was used to rate each exam for each task (1=too noisy, significantly impacted confidence to 5=excellent quality, excellent confidence). Exams were considered acceptable when at least two of the three radiologists gave a score of 3 or higher. The percentage of patients meeting this definition of acceptable was calculated for each imaging task, dose level, and tissue type (lung or soft tissue). Results: The percentages of exams considered acceptable for the purpose of lung cancer screening were 90%, 100%, 100%, 100% (lung tissue) and 85%, 100%, 100%, 100% (soft tissue) at 12.5%, 25%, 50% and 100% of original dose level. For the purpose of routine diagnostic chest CT, the percentage of acceptable exams were 75%, 95%, 100%, 100% (lung tissue) and 35%, 85%, 90%, 100% (soft tissue) at 12.5%, 25%, 50% and 100% of original dose level. Conclusions: At 25% of the dose used for routine diagnostic chest CT at our institution, acceptable image quality for the purpose of CT screening for lung cancer was achieved in 100% of the evaluated cases. This factor of 4 in dose reduction relative to routine chest exams is similar to what was used in the NLST trial.
SU‐D‐217A‐01: A High‐Resolution in Vivo Molecular Imaging Technique Based on X‐ Ray Fluorescence
Authors: Chtcheprov P , Lee Y , Lu J , Zhou O
Published: June 2012

Purpose: Traditional molecular imaging techniques such as PET/SPECT have many limitations, including relatively low spatial resolution, short lifetime of radioisotope probes, limited availability due to reliance on cyclotron, relatively high dose, and lack of effective molecular probes for certain tumor cells. In this work we demonstrate the feasibility of a novel x‐ ray fluorescence molecular imaging (XFMI) technique using high‐power carbon nanotube (CNT) x‐ray array technology. The XFMI overcomes some limitations and will be a significant advance in molecular imaging technology for cancer drug development and cancer biology research. Methods: A testing chamber was constructed containing two Amptek energy‐resolving detectors analyzing a copper collimated fluorescence beam placed opposite each other symmetric about the sample and perpendicular to the primary incoming x‐ray beam, also using the copper collimator. Different concentrations of indium trichloride and iodine were tested to determine the minimum detectable concentration (MDC) for each. Results: The MDC for indium was found to be 80 ug/mL and 100 ug/mL for iodine at 50 kVp, 30mAs (5 minutes imaging time). This is on the order of magnitude of the MDCs determined at large synchrotron facilities using XFI. Higher concentrations above 1mg/mL of both elements were detectable at 1.5 mAs (15 seconds). Conclusions: These results show that it is possible to not only measure low concentrations of the above elements, but also distinguish between similar L‐alpha peaks. This allows for future work of obtaining 2D and 3D imaging to determine element types and concentrations diffused in different parts of the body. Carolina Center of Cancer Nanotechnology, University Cancer Research Fund
SU‐D‐217A‐05: Auto‐Registration of Cardiac PET/CT Images with a 3D Weighted Gradient Correlation Algorithm
Authors: Ai H , Pan T
Published: June 2012

Purpose: To design a novel 3D automatic registration algorithm for cardiac PET/CT registration using gradient information and to evaluate the performance of the algorithm with clinical PET/CT datasets. Methods: The 512×512×47 CT images are at first resized to 128×128×47 to match the matrix size of PET. In order to maximize the gradient information at boundaries in CT, a conventional fuzzy c‐means clustering algorithm (number of cluster = 7) is implemented to suppress signals from tissues that do not contribute much useful information for the registration purpose (fat, lung, and bones). The 3D Image gradient map, consisting of all three orthogonal components, is derived from the PET images and the post‐ clustering CT images. The mis‐registration is modeled as 3D rigid body translation in this study, though it can be extended to include rotations as well. The details of the gradient‐based objective function are described in the support document. Optimal registration is determined by searching for the maximum of the objective function over a range of potential translation positions (e.g. 8.2×8.2×2.8cm). This process is repeated at a higher matrix size (512×512×47) to refine the result of registration. Results: We applied this auto registration technique on 55 patient data sets of cardiac PET/CT images. The CT images were average‐CT images, and the PET images were without attenuation correction. 54 out of the 55 cases produced satisfactory registration. Conclusions: The proposed weighted gradient correlation algorithm is a viable solution for auto registration of cardiac PET/CT images. More work is needed to further improve the robustness of thealgorithm.
SU‐D‐218‐03: Resonant Frequency of Rotating Anode X‐Ray Tubes
Authors: Shin M , Lillaney P , Hinshaw W , Fahrig R
Published: June 2012

Purpose: To evaluate a new rotating anode X‐ray tube from the resonant frequency point of view for stable and safe operation, and to validate a finite element model for insight into X‐ray tube rotor dynamics and vibration. Methods: The 3‐dimensional FEM model of the X‐ray tube motor has been developed using ANSYS and COMSOL. The resultant resonant frequency from the FEM simulation is substantiated by experiments. During deceleration of the X‐ray tube, an accelerometer and a corresponding amplifier send the time domain vibration response to a spectrum analyzer which generates the power spectrum. In the frequency domain analysis, a peak signifies large vibrations at that frequency. To corroborate the FEM model, the resonant frequency of the motor assembly without the anode attached was also measured. Lastly, a rough estimate of the resonant frequency can also be observed in angular speed curves which are obtained utilizing a quadrature position sensor. Results: The first mode resonance is expected at 20.3 Hz from the FEM simulation. This result matches closely with the peak at 22.2 Hz in the power spectrum and the location of the abrupt decreasing acceleration (slope) in the speed curve at 22 Hz. Without the anode, the FEM simulation result of 35.1 Hz is equal to the first peak at 35.1 Hz, and the angular acceleration is suddenly reduced at 34.4 Hz. Conclusions: For image‐guided interventional procedures using a hybrid system, the X‐ray tube should create flux at various times requiring repeatedacceleration and deceleration of the motor. Hence it is ideal that the resonant frequency is higher than operational speed, although alternatively the motor could accelerate through the resonant frequency quickly. Design improvements to modify the location of resonance of our motor assemblyare underway using the verified FEM model. NIH R01 EB007626, Richard M. Lucas Foundation
SU‐E‐I‐03: Scatter and Beam Hardening Correction for μCBCT Scanners Using Monte Carlo
Authors: Volken W. , Fix M.K. , Frei D. , Zulliger M.A. , Manser P.
Published: June 2012

Purpose: Micro CBCT scanners have a broad spectrum of applications in medicine and material science. However, CBCT suffers from scatter radiation and spectral effects such as beam hardening (BH). In this work an iterative BH‐ and scatter‐correction algorithm was developed using Monte Carlo (MC) methods. Methods: Two μCBCT scanner models (XtremeCT and μCT100 from SCANCO Medical AG) were simulated using EGSnrc/EGS++. The scanner measures the attenuation of X‐rays passing through the phantom and interacting in a scintillating detector. The MC method is used to characterize the influence of the scattering and BH‐ effects. In addition, an analytical model is developed in order to correct for the scattering effect. For this purpose, by using MC methods, different scatter components were analyzed with respect to the number of scatter interactions within the given geometry. For the BH‐effect, after assessing the detector response for an equivalent mono‐energetic and scatter‐free system using MC methods, an analytical correction model was developed. Both correction methods were implemented as an iterative reconstruction correction algorithm and were tested for various phantoms. Results: MC simulations show that the amounts of correction for the scattering and BH‐ effects are in the same order of magnitude. The correction term for scattering effects is a function of the scatter to primary ratio only and is mainly due to single scattered particles. The contribution of multiple scattered particles to the total scatter signal is small and can be approximated by a constant. In all cases tested, the reconstructed linear attenuation coefficients converge to the mono‐energetic reference values after 2–3 iteration steps with a deviation of about 1%. Conclusions: By using an iterative correction algorithm using single scatter approximation, BH‐ and scatter correction can be performed accurately for μCBCT scanners. This work was supported by CTI‐10629.1 and SCANCO Medical AG.
SU‐E‐I‐05: Dose Reduction in Head CBCT Examinations After Protocol Optimization
Authors: Voigt JM , Güldner C , Diogo I , Ningo A , Werner JA , Fiebich M
Published: June 2012

Purpose: CBCT systems for head examinations especially in otorhinolaryngology offer better than required image quality at relatively low purchasing costs. Due to this fact the number of dedicated head scanners increases steadily. Regarding image quality in relation to patient dose these systems are frequently not optimized. Examination parameter optimization is an iterative process, which should be done carefully by physicians in cooperation with physicists. After a successful optimization, Monte Carlo Simulations can be used to quantify the dose reduction to the patient. Methods: Images of an anatomic head phantom were obtained using different settings of kVp, mAs and rotation angle (360°, 210°). The resulting images were anonymized and the examination parameters were removed. Radiologists and otorhinolaryngologists evaluated these images and rated them into excellent image quality, good image quality, bad image quality and not readable. Based on the ratings new parameters for the adequate image quality were set. The dose reduction was calculated using Monte Carlo simulations. Results: The organ dose of radiation sensitive organs was reduced significantly. The dose reductions compared to the standard settings are: eyes: 85%, eye lenses: 88%, salivary glands: 40%, thyroid: 60%, blood vessels: 40%, brain: 60%, teeth: 80% and tonsils: 65%. Dose reduction was best, when a short scan (210° rotation angle) was used, where the eyes are not in the direct exposure field. Conclusions: The results show the potential for dose optimizations in otorhinolaryngological CBCT examinations compared to standard vendor settings without loss in diagnostic information. Furthermore this study points out the great opportunities that Monte Carlo‐based dose‐calculations methods offer to quantify the increase of dose efficiency after examination protocol optimizations. It could also be shown that CBCT has advantages when doing short scan mode around the rear head. This protects radiation sensitive organs such as the eye lenses from being directly radiated.
SU‐E‐I‐06: Measurement of Skin Dose from Dental Cone‐Beam CT Scans
Authors: Akyalcin S , English J , Abramovitch K , Rong J
Published: June 2012

Purpose: To directly measure skin dose using point‐dosimeters from dental cone‐beam CT (CBCT) scans. To compare the results among three different dental CBCT scanners and compare the CBCT results with those from a conventional panoramic and cephalomic dental imaging system. Methods: A head anthropomorphic phantom was used with nanoDOT dosimeters attached to specified anatomic landmarks of selected radiosensitive tissues of interest. To ensure reliable measurement results, three dosimeters were used for each location. The phantom was scanned under various modes of operation and scan protocols for typical dental exams on three dental CBCT systems plus a conventional dental imaging system. The Landauer OSL nanoDOT dosimeters were calibrated under the same imaging condition as the head phantom scan protocols, and specifically for each of the imaging systems. Using nanoDOT dosimeters, skin doses at several positions on the surface of an adult head anthropomorphic phantom were measured for clinical dental imaging. Results: The measured skin doses ranged from 0.04 to 4.62mGy depending on dosimeter positions and imaging systems. The highest dose location was at the parotid surface for all three CBCT scanners. The surface doses to the locations of the eyes were ∼4.0mGy, well below the 500mGy threshold for possibly causing cataract development. The results depend on x‐ray tube output (kVp and mAs) and also are sensitive to SFOV. Comparing to the conventional dental imaging system operated in panoramic and cephalometric modes, doses from all three CBCT systems were at least an order of magnitude higher. No image artifact was caused by presence of nanoDOT dosimeters in the head phantom images. Conclusions: Direct measurements of skin dose using nanoDOT dosimeters provided accurate skin dose values without any image artifacts. The results of skin dose measurements serve as dose references in guiding future dose optimization efforts in dental CBCT imaging.
SU‐E‐I‐10: Putting Teeth into Your CT Dosimetry Program: Approaches to Cone‐ Beam Dental/Maxillofacial CT Dosimetry
Authors: Blackburn T , Gallet J , Guild J , Arbique G , Anderson J A
Published: June 2012

Purpose: To review and compare different approaches to the problem of dosimetry for limited field‐of‐view (FOV) cone beam CT devices for dental and maxillofacial applications. Methods: The determination of patient doses from specialized, cone‐beam CT devices for dental and maxillofacial work requires medical physicists to re‐evaluate their dosimetry methods. These devices work in cone‐beam geometry, with an axial field dimension on the order of the lengths of the standard head CTDI phantom and pencil ionization chamber. They may also utilize less than 360 degree scans, resulting in asymmetrical radiation distributions. This operating regime is far from that for which conventional CT dosimetry was designed, and alternative approaches must be considered. The alternatives include extensions of conventional CT dosimetry currently used for large axial FOV scanners (e.g. the extended CTDI parameter (CTDIe) for the Toshiba Aquillion One with 160 mm axial FOV) and the new method based on point dosimetry measurements recently formalized in AAPM Report TG‐111. Conventional, modified‐conventional, and TG‐111 dosimetry measurements are used in two CT dose phantoms (adult head and pediatric head) to obtain dose indices for the Planmeca ProMax 3D Max dental CT scanner. Surface dose maps are generated using radiochromic film for correlation with the chamber dosimetry. Results: Results for the three dosimetry approaches are compared for the specific case of the ProMax 3D Max scanner. Strengths and weaknesses of the three measurement paradigms for this type of application are compared. Conclusions: The increasing availability of specialized scanners operating in full cone‐beam mode will require the clinical medical physicist to be conversant with extensions to the CT dose index methodology suitable for this equipment.
SU‐E‐I‐13: Evaluation of CT Number with Changing Scan Parameters for Nucletron Simulix Evolution CBCT
Authors: Gardner S , Li J , Xiao Y , Studenski M
Published: June 2012

Purpose: To quantify the variation in CT number generated by the Simulix Evolution CBCT with changes in scan length and phantom thickness. Methods: Three phantoms were used in this study: CIRS Model 610 AAPM CT Phantom, Gammex 467 Tissue Characterization Phantom, and Catphan 600 phantom. The AAPM Phantom was used to assess the variation of HU with phantom thickness. Scans were acquired with two field size settings (full‐ and half‐beam) with and without a 3.5 cm thick ring. The Catphan and Gammex phantoms were used to assess the Simulix's capability of producing a consistent CT‐to‐ED conversion table with different scan lengths, ranging from 1 cm (very thin) to 20 cm (clinical use). The data were also compared to data acquired with our in‐house CT Sim (GE HiLite LightSpeed 16 slice). Results: The AAPM phantom scans with and without the ring yielded an average difference in HU of 145 HU (full‐beam) and 74 HU (half‐beam) for each of five inserts. The HU for Cortical Bone (SB3) [largest Gammex electron density insert; 1.69] ranged from 923 to 1170 HU for the 4 cm and 1 cm scan lengths, respectively. The HU for Teflon [largest Catphan electron density insert; 1.867] ranged from 657 to 951 for the 20 cm and 1 cm scan lengths, respectively. The HU for air in Catphan ranged from −749 to −905, and the HU for LDPE [electron density 0.944] ranged from −82 to −42, for the 20 cm and 1 cm scan lengths, respectively. Conclusions: Results show a large variability in the calculated CT number with differences in phantom thickness, as evidenced by the results with the AAPM phantom. In addition, there appears to be a dependence on scan length, attributed to increased scatter contribution. Further tests will be done to evaluate the appropriateness of the use of the Simulix CBCT unit for heterogeneity corrected external beam treatment planning. The author has received no funding during the course of this research.
SU‐E‐I‐18: Variability of Physiological Parameters Estimated by AATH and MTK Models in DCE‐MRI
Authors: Liu C , Liao Y , Liu H
Published: June 2012

Purpose: To assess the accuracy and precision of physiological parameters estimated by the modified Tofts and Kermode (mTK) model and the adiabatic approximation to the tissue homogeneity (AATH) model in dynamic contrast enhanced (DCE) MRI. Methods: Computer simulations were performed using the arterial input function (AIF) from Parker et al., and the multiple indicator, multiple path, indicator dilution 4 region (MMID4) model for simulating the tissue concentration time curve. A set of physiological parameters, simulating a breast tumor, was selected as the input to the MMID4. The output was then converted to signal time curve using SPGR signal equation. Four levels of Gaussian noise, corresponding to SNRs of 100, 50, 20 and 10, were added to the signal time curves, with 1000 iterations each. These curves were then transferred back to concentration time curves on which mTK and AATH models were applied for fitting. For AATH model the mean transit time (tau) was held as a fixed parameter ranged from 2 to 10 s, and the final solution was selected based on minimizing the root mean square error. Results: For common parameters obtained by both models (Ktrans, Ve, Vp), AATH provided better accuracy, which agreed with the literatures, whereas mTK resulted in superior precision. As expected, greater coefficient of variation (CV) was found with smaller SNR in all cases. For the parameters that could only be obtained with the AATH model, the CVs were less than 10% for F, E and PS, and around 20% for tau, at the SNR level of 20. Conclusions: Using the MMID4 model for data simulation, this work found that AATH model was more accurate but less precise for estimating physiological parameters as compared with mTK model. The AATH model was able to separate blood flow and permeability estimates with reasonable errors and variations.
SU‐E‐I‐19: Local Search Clustering Algorithm for DCE‐MRI Analysis
Authors: Hui C , Narayana P
Published: June 2012

Purpose: To develop a local search clustering algorithm for analyzing the dynamic contrasted enhanced (DCE)‐MRI data for determining the vascular permeability. The clustered signal will have better contrast‐to‐noise ratio (CNR) and thus can improve the analysis. Methods: In DCE‐MRI, data often suffer from low CNR. The CNR is particularly poor in central nervous system and could lead to spurious results. We propose a local search clustering algorithm that groups proximal voxels with similar uptake curves and T1 values. The algorithm starts with a seed voxel, and then grows outward to recruit new voxels into a cluster. Once a cluster is formed, all members of the current cluster form a ‘seed collection’ and the seed point of the cluster becomes the seed collection. The expansions and updates continue with the seed point/collection until the stopping criterion is met. To investigate the effectiveness of our clustering algorithm, we used a 64×64 2D Shepp‐Logan phantom. Variations on the T1 values and permeability parameters were applied on different regions in the phantom. The time resolution was set to 30sec and 82 post‐contrast data were created. After the DCE‐MRI data were generated, Gaussian noise was applied to the images to investigate the effect of noise on the clustering algorithm. DCE analysis was performed on the clustered data and the results were compared against the Result obtained from voxel‐by‐voxel analysis. Results: The addition of noise degraded the results of DCE estimation. The clustering algorithm on average reduced the errors of the permeability parameters by more than 50% compared to the voxel‐by‐voxel analysis. Conclusions: We developed a local search clustering algorithm to segment the concentration time curves of the DCE‐MRI data. The proposed clustering algorithm enhances the apparent CNR within the clustered data and reduces the errors of the permeability parameters.
SU‐E‐I‐27: Effect of Focal Spot Choice on the System Performance of a High‐ Resolution Micro‐Angiographic Fluoroscope (MAF) Detector
Authors: Jain A , Panse A , Ionita C , Bednarek D , Rudin S
Published: June 2012

Purpose: The generalized metrics of GMTF and GDQE were used to evaluate the effect of focal‐spot choice on system performance of the Micro‐ Angiographic Fluoroscope (MAF) imager with a geometric magnification common for neuro‐endovascular interventions. Methods: The MAF, a newly developed high‐resolution detector with very low instrumentation noise and large variable gain, was used for the study. It has 35‐micron pixels and a 500‐micron thick CsI HR‐type phosphor. The detector MTF was measured using the slanted edge method and the focal spot MTF's were measured using a standard pin‐hole assembly. For the comparison analysis, the GMTF and GDQE were determined for three different focal spots (0.3 mm, 0.5 mm and, 0.8 mm) with a magnification factor of 1.25. A stainless‐ steel stent was also imaged with the same magnification for all three focal spots. Results: The MAF's performance is affected significantly by the choice of focal‐spot size because of its very high resolution. The GMTF and GDQE comparison for three focal spots showed significant degradation, increasing from small to large focal spot. The GMTF values were found to be 0.09, 0.05 and 0.01 at 5 cycles/mm for the small, medium and large focal spot, respectively. The corresponding values for GDQE were 0.1, 0.03 and 0.001. These results demonstrating the effect of choice of focal spot on the image quality are supported by line profiles obtained across the stent images. Conclusions: The results of this study demonstrate the significance of focal‐spot size on system performance when using a high‐resolution detector with a realistic magnification and shows the importance of choosing the minimum focal‐spot size. (Support: NIH‐Grant R01EB002873) NIH Grants R01‐EB008425, R01‐EB002873 and an equipment grant from Toshiba Medical Systems Corp.
SU‐E‐I‐28: Development of Graphic Patient Models for a Real‐Time Skin Dose Tracking System (DTS) for Fluoroscopic Interventional Procedures
Authors: Rana V , Bednarek D , Wu J , Rudin S
Published: June 2012

Purpose: To develop a library of graphic human models that closely match patients undergoing interventional fluoroscopic procedures in order to obtain an accurate estimate of their skin dose. Methods: A dose tracking system (DTS) has been developed that calculates the dose to the patient's skin in real time during fluoroscopic procedures based on a graphical simulation of the x‐ray system and the patient. The calculation is performed using a lookup table containing values of mGy per mAs at a reference point and inverse‐square correction using the distance from the source to individual points on the skin. For proper inverse‐square correction, the external shape of the graphic should closely match that of the patient. We are in the process of developing a library of 3D human graphic models categorized as a function of basic body type, sex, height and weight. Two different open‐ source software applications are being used to develop graphic models with varying weights and heights, to ‘morph’ the shapes for body type and to ‘pose’ them for proper positioning on the table. The DTS software is being designed such that the most appropriate body graphic can be automatically selected based on input of several basic patient dimensional metrics. Results: A series of male and female body graphic models have been developed which vary in weight and height. Matching pairs have been constructed with arms at the side and over the head to simulate the usual placement in cardiac procedures. The error in skin dose calculation due to inverse‐square correction is expected to be below 5% if the graphic can match the position of the patient's skin surface within 1 cm. Conclusions: A library of categorized body shapes should allow close matching of the graphic to the patient shape allowing more accurate determination of skin dose with the DTS. Support for this work was provided in part by NIH grants R43FD0158401, R44FD0158402, R01EB002873 and R01EB008425, and by Toshiba Medical Systems Corporation.