bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Analysis of the Dynamic Characteristics of a Hybrid Aerostatic Bearing
Authors: Rudloff Laurent , Arghir Mihai , Bonneau Olivier , Guingo Sébastien , Chemla Guillaume , Renard Emelyne
Published: June 2012

The dynamic characteristics of a hybrid aerostatic bearing are experimentally investigated on a test rig consisting of a rigid rotor driven by an impulse turbine. The rotor is horizontally mounted and is supported by two identical aerostatic bearings. Both the impulse turbine and the aerostatic hybrid bearings are fed with air. The feeding pressures in the bearings can be as high as 7 bars and rotation speeds can reach 60 krpm so the dynamic load on the rotor is much larger than the static load engendered by its weight. Excitations are applied either via an impact hammer or via unbalancing masses. The measuring instruments record the bearing feeding pressures, the rotation speed, the impact force, the displacements of the two bearings, and the bearing housing accelerations. The experimental data together with the equations of motion of the rotor enables the identification of the dynamic coefficients of the bearings. A second identification procedure using the same impact hammer is also possible as force transducers are mounted between the bearing housing and its support. The dynamic coefficients of the bearings can then be obtained from the equation of motion of its housing. Unbalance response provide a convenient way for verifying the accuracy of the identified dynamic coefficients. Therefore these coefficients are injected in the equations of motion of a four degrees of freedom rigid rotor and the theoretical results are compared with values measured on the test rig. Comparisons show that predictions are acceptable but become less accurate at high rotation speeds where large dynamic forces are needed for exciting the corresponding synchronous frequencies.
Heat Conduction Through Eccentric Annuli: An Appraisal of Analytical, Semi-Analytical, and Approximate Techniques
Authors: Kumar Moharana Manoj , Kumar Das Prasanta
Published: June 2012

The problem of conduction heat transfer through an eccentric annulus with the inner surface kept at a constant temperature and the outer surface subjected to convective condition is solved by three different techniques. A perturbation analysis yields an analytical expression for temperature profile for small values of eccentricity. The two dimensional conduction problem has also been solved by a two dimensional semi-analytical technique in which the condition at the outer periphery is matched by a collocation technique. Finally, a one dimensional approximate technique namely sector method has been used to solve the same problem. The sector method does not require any numerical technique yet yields remarkable accuracy. Next, the heat flow through an eccentric insulation surrounding a circular cylinder was considered. It has been demonstrated that the sector method is effective also in determining the geometry of the critical insulation in this case over a wide range of radius ratio and Biot number. Finally, both all the three methods, i.e., the perturbation technique, the boundary collocation method and the sector method have been applied to determine the geometry of the critical as well as crossover perimeter of insulation around a circular cylinder when the insulation is provided eccentrically.
New Feature Extraction Method for the Detection of Defects in Rolling Element Bearings
Authors: Xiang Ling , Hu Aijun
Published: June 2012

This paper proposes a new method based on ensemble empirical mode decomposition (EEMD) and kurtosis criterion for the detection of defects in rolling element bearings. Some intrinsic mode functions (IMFs) are presented to obtain symptom wave by EEMD. The different kurtosis of the intrinsic mode function is determined to select the envelope spectrum. The fault feature based on the IMF envelope spectrum whose kurtosis is the maximum is extracted, and fault patterns of roller bearings can be effectively differentiated. Practical examples of diagnosis for a rolling element bearing are provided to verify the effectiveness of the proposed method. The verification results show that the bearing faults that typically occur in rolling element bearings, such as outer-race and inner-race, can be effectively identified by the proposed method.
Phase identification and control of thin films deposited by co-evaporation of elemental Cu, Zn, Sn, and Se
Authors: Vora Nirav , Blackburn Jeffrey , Repins Ingrid , Beall Carolyn , To Bobby , Pankow Joel , Teeter Glenn , Young Matthew , Noufi Rommel
Published: June 2012

Kesterite thin films [(i.e., Cu2ZnSn(S,Se)4 and related alloys] have been the subject of recent interest for use as an absorber layer for thin film photovoltaics due to their high absorption coefficient (>104 cm−1), their similarity to successful chalcopyrites (like CuInxGa1−xSe2) in structure, and their earth-abundance. The process window for growing a single-phase kesterite film is narrow. In this work, we have documented, for our 9.15%-efficient kesterite co-evaporation process, (1) how appearance of certain undesirable phases are controlled via choice of processing conditions, (2) several techniques for identification of phases in these films with resolution adequate to discern changes that are important to device performance, and (3) reference measurements for those performing such phase identification. Data from x-ray diffraction, x-ray fluorescence, Raman scattering, scanning electron microscopy, energy dispersive spectroscopy, and current-voltage characterization are presented.
Impact of ultrathin Al2O3 interlayer on thermal stability and leakage current properties of TiO2/Al2O3 stacking dielectrics
Authors: Wang Hong-Bo , Ma Da-Yan , Ma Fei , Xu Ke-Wei
Published: June 2012

Ultrathin TiO2/Al2O3 stacking structures were fabricated using an atomic layer deposition technique. The effect of the ultrathin Al2O3 interlayer on interfacial thermal stability and leakage current properties were studied. After thermal annealing of the TiO2/Al2O3/TiO2/Al2O3/Si structure at 700 °C for 60 s, the Al2O3 double layers remained amorphous, although the layers of TiO2 were crystallized. The amorphous Al2O3 divided the grain boundaries which would otherwise serve as diffusion paths for atoms and as leakage current channels from the TiO2 layers. As a result, atomic diffusion and surface roughness were suppressed, and the leakage current value was reduced by about a 1.5 order of magnitude compared with TiO2/Al2O3/Si. The improved interfacial stability as well as the reduced leakage current density indicates the present stacking structure has potential application in future high-performance microelectronics.
SU‐A‐BRB‐01: Medical Physics and Technology Education for Society: Adults, Teenagers, and Elementary Students
Authors: Sprawls P , Fox M
Published: June 2012

Providing medical physics education to the general society has two valuable goals. For adults it helps them develop an understanding of medical science, technology, and clinical applications that they might encounter and have a better comprehension of a variety of scientific and technical issues in the news media. For students it enhances their interest in physics by showing applications that provide major benefits to society and introduces possible career paths. In the first part Perry Sprawls describes educational activities for adults. A course generally begins with the principles of the various imaging modalities with an emphasis on what can be visualized with each and typical clinical applications. The principles of modern radiation therapy are included with special attention to terminology associated with the various methods. There is always an interest in the effects of radiation so that is included with emphasis of benefits to risk. I always include one class on cardiac electronics, a special interest of mine, and plan to add a session on the physics and technology associated with hearing in future programs.Google Images is an excellent resource that can provide extensive visuals for courses of this type. Community senior‐adult lifelong learning courses and programs sponsored by Road Scholar, formerly ElderHostel, provide opportunities for medical physicists to share their knowledge and experience with citizens in their local communities. The second half of this symposium, given by Mary Fox, will focus on the elementary & high school age group. How do you educate young students about the career of medical physics? A sample presentation along with ideas for speaking to both these age levels will be demonstrated.

Learning Objectives:

1. Provide adults with the knowledge to understand various medical procedures and effectively communicate with medical professionals.

2. Enhance the ability of adults to understand a variety of scientific and technological issues that are in the news

3. Provide the medical physicists with examples of presentation material for elementary and high school age groups.
SU‐C‐211‐01: Effect of Contour Accuracy on DVH Parameters
Authors: Zhao A , Godley A
Published: June 2012

Purpose: Dose Volume Histograms (DVH) are the main assessment of IMRT plans, yet they rely on organ contour accuracy. This study quantifies the change in DVH parameters caused by systematic modification of contours to replicate typical inter‐observer and auto‐contouring errors. Methods: Eight prostate patients planned for 78 Gy IMRT with margins of 8 mm, (6 mm anterior and posterior) were selected. Prostate contours were uniformly expanded by ±1 and 2 mm, bladder contours uniformly by 1 and 2 mm and in the posterior and inferior by ±1, 1.5 and 2 mm, and rectum contours uniformly by 1 and 2 mm and anteriorly by ±1 and 1.5 mm. This simulated typical contouring errors due to low contrast at the prostate and bladder/rectum borders. The following DVH parameters were calculated for the rectum and bladder contours: V70 and V60 (% and cc), and prostate contours: D100, D98 and mean dose. Results: For prostate, the contour error had no substantial effect on the DVH. For bladder, at the 1 mm level, the deviations in V70 and V60(%) are below 4.6% and for rectum below 7.1%. The bladder, and particularly rectum, showed dramatic (22–56%) increase in absolute volume (cc) receiving 60 and 70 Gy when contour errors were greater than 1 mm, but this absolute change is <12.4% with errors <1 mm. Because V70 and V60 are initially small in the plan, the <12.4% increase was still clinically acceptable. When a 4 mm (2 mm anterior and posterior) margin plan was assessed, the prostate D100 deviation at 1 mm is still <1%, while bladder and rectum deviation were reduced, implying 1 mm accuracy is a robust target level. Conclusions: Agreement between contours of 1 mm must be achieved to ensure comparable DVHs. Changes in the DVH occur precipitously above this level.
SU‐C‐211‐04: Evaluation of IMRT and VMAT Treatment Plan Quality Delivered with and Without Flattening Filter Using Pareto Optimal Fronts
Authors: Lechner W , Kragl G , Georg D
Published: June 2012

Purpose: To evaluate treatment plan quality of IMRT and VMAT plans for high energy photon beams delivered with (FF) and without (FFF) flattening filter. Methods: 9‐field IMRT and 360° single arc VMAT plans, based on 10 MV beams with and without flattening filter, were created using Monaco (Elekta/CMS, v.2.04, USA) for three different patients (prescribed PTV dose 78 Gy). This treatment planning systems was commissioned for FF and FFF beams provided by an Elekta linac. The Pareto optimal fronts were created by calculating different treatment plans with varying rectum constraints and evaluating the PTV volume receiving less than 95% of the prescribed dose (V <95%) and the volume of the rectum receiving 70Gy or more (V 70Gy). Treatment plan efficiency was evaluated by recording number of monitor units (MUs) and by measuring the delivery time (T) using an Elekta Precise linear accelerator in FF and FFF mode. Results: The POFs of the rectum for both IMRT and VMAT in FFF mode were similar or even superior to the FF‐ modalities. For two of the three patients the POFs of IMRT and VMAT revealed a systematic difference of about 2% in target coverage. The POFs of the remaining patient showed virtually no difference for all four modalities. The delivery time of IMRT FFF decreased by about 23% compared to IMRT FF. In contrast to the IMRT techniques, delivery time increased by 20% when using VMAT FFF compared to VMAT FF. Conclusions: The evaluation of the POFs confirms that a flattening filter is not necessary for static and rotational IMRT treatments. Similar studies are needed for other IMRT indications, like head‐and‐neck cancer, to draw final conclusions. Sequencing algorithms for FFF‐beams need to be optimized and further improvement of the mechanical MLC properties are desirable for VMAT in FFF mode. Corporate sponsored research by Elekta
SU‐C‐213AB‐01: Application of Ultra‐Fast Dose Calculation in Real‐Time Interactive Treatment Panning
Authors: Ziegenhein P , Kamerling C , Heinrich H , Oelfke U
Published: June 2012

Purpose: We are investigating a new treatment planning paradigm: realtime planning via interactive dose shaping (IDS). IDS is a universal two‐step process: First, a desired local dose variation is imposed for a 3D dose distribution by adjusting the correspondent fluence amplitudes. This dose modification inevitably causes unwanted dose changes outside the considered local dose area. Thus, second, a recovery strategy is applied to compensate for these unintended changes, so that the initial modification only has an influence on the desired region of the plan. The planning process could be carried out as a sequence of this Dose Modification and Recovery (DMR) steps. For implementing DMR strategies in realtime an ultra‐fast local dose calculation within a few milliseconds is needed for evaluating the incrementally modified dose distribution. Methods: The fast dose calculation algorithm is based on a pencil beam convolution technique using a set of measured pencil beam kernels whose convolutions with the beam fluence are carried out in a discretized spatial domain. This leads to three key features for our algorithm: i) A spatial‐limited modification of fluence amplitudes requested by the DMR strategy can be considered as a relatively small incremental term to the convolution in space domain ii) The discrete convolution consists of simple multiply‐add operations which are highly optimized on modern CPU and GPU hardware. iii) The trade‐off accuracy/runtime can be adapted selectively for each fluence region of interest by controlling the radius of the finite pencil beam kernel. Results: The runtime of dose updates over a fluence area of 20×20 mm is about 10 ms on a Intel i7 CPU with an accuracy of 1% in the high dose region. Conclusions: It could be shown that the proposed method of local dose update calculation is fast and accurate enough for our interactive realtime dose shaping planning approach.
SU‐C‐213AB‐05: IMRT QA Using R&V Data, Treatment Records, and a Second Treatment Planning System
Authors: Ohrt J , Balter P , Court L , Gillin M
Published: June 2012

Purpose: Traditional patient‐specific IMRT QA measurements are labor intensive and consume machine time. Calculation‐based IMRT QA methods typically are not comprehensive. We have developed a comprehensive calculation‐based IMRT QA method to detect uncertainties introduced by the initial dose calculation, the data transfer through the R&V system, and aspects of the physical delivery. Methods: We recomputed the treatment plans in the patient geometry for 48 cases using data from the R&V, and from the delivery unit to calculate the ‘as‐transferred’ and ‘as‐delivered’ doses respectively. These data are sent to the original TPS to verify transfer and delivery or a second TPS to verify the original calculation. For each dataset we examined the dose computed from the R&V record (RV), from the delivery records (Tx), and dose computed with a second verification TPS (vTPS). Each was compared to the clinical dose distribution using 3D gamma analysis and by comparison of mean dose to target volumes. 24 plans were also compared against measurement‐based QA. Results: The average percentage of voxels with passing gamma values for 3%‐3mm, 2%‐ 2mm, and 1%‐1 mm criteria for the RV plan were 100.0 (s=0.0), 100.0 (s=0.0), and 100.0 (s=0.1); for the Tx plan were 100.0 (s=0.1), 99.9 (s=0.6), and 96.0 (s=4.6); and for the vTPS plan were 99.3 (s=0.6), 97.2 (s=1.5), and 79.0 (s=8.6). The average ratio of the mean dose for all target volumes in the RV, Tx, and vTPS plans to the clinical value was 0.999 (s=0.001), 1.008 (s=0.006), and 0.991 (s=0.009). The average calculation‐to‐measurement ratios were 0.997 (s=0.014), 0.997 (s=0.014), 1.004 (s=0.015), and 0.991 (s=0.016) for clinical, RV, TR, and vTPS plans. Conclusions: Together with mechanical and dosimetric QA of the treatment unit, our methods for calculative‐based IMRT QA promise to minimize the need for patient‐ specific QA measurements by indentifying outliers in need of further review. Research sponsored by Philips Medical Systems
SU‐C‐213AB‐06: Validation Study of the Accuracy of the Transform Method for Clinically Intuitive Quality Assurance
Authors: Norris H , Thomas A , Oldham M
Published: June 2012

Purpose: Per‐beam quality‐assurance (QA) methods (e.g. portal dosimetry) have been shown to be inadequate for reporting the clinical significance of delivery errors or deviations. Recently we presented a novel ‘transform’ method which can solve this problem utilizing 3D dosimetry techniques. Here, we evaluate the accuracy of this method under various conditions. Methods: A range of known mechanical and delivery errors were introduced on three stereotactic IMRT head‐and‐neck patient treatment plans (e.g. gantry, collimator, and couch +/−5°, Dose normalization +/−5%). Verification plans were then created where the error plans were recomputed onto an RPC head‐phantom containing a 3D dosimeter. The phantom dose distribution was then transformed back to the patient CT data using the new transform method. The accuracy of the transform method was evaluated in 3D by comparison of this transformed distribution with a direct calculation from the original patient plan but incorporating the error. Comparison metrics included DVH, gEUD, and gamma. Results: Gamma passing rates were calculated with 2% dose difference/ 2mm distance‐to‐agreement criteria. Comparing the transformed dose distribution estimate with the true error dose distribution, global gamma passing rates were above 97% for all plans with an average passing rate of 99.33%. The passing rates were above 99% for all organ and target structures. A gEUD was calculated for each structure, and the average percent difference was found to be less than 4%. Conclusions: Even when presented with substantial errors, the new transform method robustly predicted the clinical significance of these errors through DVH, gamma, and other clinical metrics (e.g. gEUD). These promising verification results are an important step toward validating a new approach to QA which enables the clinical significance of QA data to be evaluated.
SU‐C‐BRCD‐05: A Failure Mode and Effects Analysis (FMEA) Approach for Craniospinal Irradiation (CSI) with Proton Therapy (PT)
Authors: Cheng C , Allgower C , Simmons J , Conley T , Das I , Zhao L , Zhao Q , Johnstone P , Buchsbaum J
Published: June 2012

Purpose: In this paper, we report an FMEA approach on CSI at the IU Health Proton Therapy Center. Methods: A process map in proton CSI is developed. Each process consists of a number of sub‐processes. For each sub‐process, possible failures that may affect the process are identified and their respective Risk Priority Number (RPN) are calculated based on their severities (S), likelihood of occurrence (O) and probability of being detected (D), following the TG100 guidelines. Failures that most adversely impact the treatment are identified and quality assurance procedures to safeguard these most serious failures are developed. Attention is also given to certain failures which have low RPN but which may have dire consequence if it occurs in a treatment. Results: Ten intermediate processes involved in the CSI are identified. The number of sub‐processes within each intermediate process varies, from as few as one to as many as 11. For the ten processes in PTCSI, there are total of 66 sub‐processes, 139 failure modes and 561 causes of failures. 6/10 processes have failures with RPN=300. Examples of failures with such large RPN values are errors in administering anesthesia, in‐correct patient setup for image guidance, problems in the handling of apertures and compensators, etc. Conclusions: The implementation of FMEA in CSI (or any treatments) is a team effort. Significant efforts are involved in setting up process trees, failure modes, estimating the RPN values for each cause of failures, etc. However, once a FMEA is properly aligned, it is relatively easy to identify the most critical factors that require special attentions or QA to ensure safe execution of the processes. A learning curve to implement FMEA in any radiation oncology department should be expected given the different analysis practice from traditional QA approaches.
SU‐C‐BRCD‐06: A Method of Streamlined Failure Mode and Effect Analysis to Improve Patient Safety
Authors: Ford E , Smith K , Keck J , Harris K , Terezakis S , Sibley G
Published: June 2012

Purpose: Failure Mode and Effects Analysis (FMEA) provides a proactive method of improving the quality and safety of treatments by identifying and correcting hazards points in the process of clinical care. FMEA, however, is often thought to be prohibitively labor intensive. This study outlines a method of streamlined FMEA, conducted with limited resources, and assesses its feasibility and effectiveness. Methods: FMEA was performed on the external beam service of a clinic treating approximately 650 patients per year on three linear accelerators. A facilitator and local team leader were identified, and a plan was developed to complete the exercise in four one‐ hour meetings as follows: 1 (core group), introduction and process mapping, 2 (all staff) identification of failure modes from expert user input, 3 (core group) scoring of failure modes according to an FMEA risk priority number, RPN, i.e. the product of severity, occurrence and detectability scores, and 4 (all staff) error proofing of the top‐five ranked failure modes. Results: Fifty‐ two failure modes were identified, 43 of which were scored and ranked. Specific interventions were developed for the five highest ranked failure modes. FMEA scoring after intervention indicated that the average RPN score for the top five modes decreased from 273 to 161 (p=0.03) while FMEA scoring of a control group of failure modes with no intervention did not show a significant change in RPN (p=0.07). The exercise was accomplished within the expected timeline and required 55 total hours of staff time and 20 hours of facilitator effort. Conclusion: Streamlined FMEA analysis is feasible with a relatively modest effort, and can reduce the risk profile of a facility. This may open the possibility of performing repeat FMEA on a regular basis.
SU‐C‐BRB‐02: Exploring the Correlation Between 3D Spatial Dose Distribution and Toxicity in Normal Tissue
Authors: Saleh Z , Apte A , Sharp G , Rao S , Lee N , Deasy J
Published: June 2012

Purpose: To explore the correlation between spatial dose distribution and toxicity of normal tissue by mapping 3D dose distribution onto a reference patient. Methods: In order to facilitate the direct correlation between dose to a certain tissue sub‐volume and toxicity, 3D dose distributions of a patient cohort are deformed onto a single reference patient using deformable image registration. Spatial Spearman rank correlations between warped dose and toxicity are then computed on a point‐by‐point basis over the entire voxel space of the reference patient. We illustrate this approach using a cohort of 37 right‐sided H&N cancers of the oropharynx regarding the endpoint of trismus. Patients were treated with definitive IMRT and concurrent chemotherapy with a prescription dose of 70 Gy between Jan. 2004 and April 2009 at MSKCC with a median follow‐up time of 34 months (range, 6–68). 12 patients developed trismus (Grade >=1). Dose volume histograms (DVH) of the mastication muscles were also exported to perform logistic regression. Results: The standard logistic regression model based on DVH derived parameters for contoured muscles provided a moderate Spearman correlation (Rs=0.45, p<0.05). Meanwhile, examining the 3D Spearman map reveals a region with high correlation (Rs=0.58, p<0.001). Interestingly, a close up view shows that this potentially ‘radio‐sensitive’ region is located on the contralateral side at the attachment point of the medial and lateral pterygoid muscles with the pterygoid plate. Conclusions: This study demonstrates the feasibility of studying the spatial correlation between dose and toxicity in normal tissues. The validity of this method was demonstrated in H&N patients. This technique preserves the spatial information of the dose distribution and provides an unbiased approach to identify critical anatomic structures since it does not require prior assumptions about the organs at risk. In addition, this method is generic and can be extended to study other complication endpoints. Partially supported by NIH grant ROI CA85181
SU‐C‐BRB‐03: Modeling of Radiation‐Induced Sensorineural Hearing Loss from IMRT and Chemotherapy for Nasopharyngeal Carcinoma
Authors: Tai A , Wang J , Bao Y , Chen M , Li X
Published: June 2012

Purpose: To model and predict radiation‐induced Sensorineural Hearing Loss (SNHL) from intensity modulated radiation therapy (IMRT) and cisplatin‐based chemotherapy for patients with nasopharyngeal carcinoma (NPC). Methods: Audiometry data of 53 patients (106 ears) treated with the chemoradiation therapy were collected with a median follow‐up time of 60 (28–84) months. Among them, 15 SNHL cases were observed. The correlation of the SNHL data with the dose volume histograms (DVH) of both inner ear and cochlea, chemotherapy dose and patient age for each patient were analyzed using the Lyman‐Kutcher‐Burman (LKB) model and relative seriality (RS) model with a modification to include the impacts from the cisplatin dose and patient age. There are 5 parameters in each model which were determined by a maximal likelihood fitting of the clinical data. Results: Both models fit the data reasonably well, indicating that SNHL is correlated to the volume and radiation dose to cochlea, thus, to inner ear. This correlation is modified by chemotherapy dose and patient age. TD50(1) is approximately 300 Gy when only radiation is considered and is 72 Gy when patient aging and the cisplatin dose are included. The parameter n and m in the LKB model and s and γ in the SR model were obtained to be n=0.035±0.010, m=0.45±0.11 and s=2.05±1.75, γ =0.71±0.15 averaged over those obtained using DVHs of the cochlea and inner ear. A multivariate analysis found that the normal tissue toxicity probability (NTCP) calculated by the models is a statistically significant factor to predict the ototoxicity rate. The modeling results show that both inner ear and cochlea have the characteristics of a serial organ in terms of radiation dose response. Conclusions: The biophysical models derived in this study can predict the incidence of SNHL and may be used to optimize radiation treatment plans to reduce SNHL.
SU‐C‐BRB‐05: Accounting for Anisotropic Growth of Glioma in Radiotherapy Planning
Authors: Unkelbach J , Menze B , Konukoglu E , Motamedi A , Ayache N , Shih H
Published: June 2012

Purpose: We study a phenomenological tumor growth model for improved target volume definition for radiotherapy of glioblastoma. Currently, an isotropic margin is added to the visible tumor to account for microscopic tumor cell infiltration in normal appearing brain tissue. However, it is known that glioma growth is not isotropic. The ventricular system and the dura, including falx cerebri and tentorium cerebelli, represent anatomical barriers for migrating cells. Such anatomical constraints are currently not consistently and quantitatively incorporated in target delineation. Methods: We assume that tumor growth is characterized by local proliferation of tumor cells and diffusion into neighboring tissue. Mathematically, this can be described via a partial differential equation of reaction‐diffusion type, the Fisher‐Kolmogorov‐Equation. Anatomical constraints are modeled via no‐ flux boundary. Solving the model equations provides a three‐dimensional distribution of the tumor cell density. The radiotherapy target can be defined as an iso‐line of the cell density. Results: Two specific questions were investigated: First, tumor locations in which the model may be particularly useful have been identified; and second, a sensitivity analysis with respect to the model inputs was performed. Tumors located in proximity to the falx cerebri may benefit: The model is able to describe both the falx as a boundary and the corpus callosum, which provides a route for tumor cells to spread to the contralateral hemisphere. This effect is often not consistently accounted for in manual target delineation. Among all model parameters, correct segmentation of the brain is a critical prerequisite. Conclusions: The tumor growth model represents a tool to objectively create target volumes for radiotherapy of glioblastoma by consistently accounting for known growth patterns. All model inputs can be linked to model outputs, making it possible to assess the impact of uncertainties ‐ an essential step for an application in clinical practice.
SU‐C‐BRB‐06: Modeling Stereotactic Body Radiation Therapy (SBRT) including Cell Cycle‐Dependent Radiosensitivity, Hypoxia, Reoxygenation and Proliferation: Is SBRT Explainable Based on Classical Radiobiological Factors?
Authors: Jeong J , Deasy J O
Published: June 2012

Purpose: The tumoricidal effectiveness of standard fractionation radiotherapy is usually understood qualitatively in terms of proliferation, hypoxia, and reoxygenation. We have developed a novel, state‐based computational model that includes those factors. The efficacy of SBRT has been hypothesized to be due to other factors, such as apoptosis of vasculature and/or immune‐response factors. The goal of this project is to see if SBRT can potentially be explained using only those classical radiobiology factors. Methods: The state‐based computational model considers the cell cycle effect on radiosensitivity and cycle reassortment. Varying fractionation schemes were compared in terms of model predicted equivalent dose at 2 Gy/fx (EQD_model). Using relevant parameters for lung cancer tumors, the EQD model was estimated for several typical SBRT regimes. Results: SBRT is predicted to benefit from less repopulation (as expected) and high cell‐kill relative effectiveness, but is also predicted to suffer from less reoxygenation and the absence of cell‐ cycle reassortment. Overall, the model predicted EQD_model was significantly reduced from the BED‐based NTD2 (NTD2=BED/1.2, assuming alpha/beta=10), typically by about 25–30%. The treatment duration of SBRT affected the treatment efficacy and the ratio of EQD_model/NTD2 was lowest for high dose single fraction SBRT (∼60%). With longer treatment duration, the EQD_model increased and approached to NTD2, due to increased reoxygenation. For most evaluated SBRT regimens, predicted cell‐survival levels were too high to account for the reported high local‐response rates of the SBRT outcomes. Conclusions: Considering four Rs of radiobiology, the equivalent dose in 2 Gy/fx was estimated for several SBRT regimes. The treatment efficacy of SBRT estimated from BED is significantly overestimated compared to the model results and the SBRT schedule seems to affect the treatment efficacy. Non‐ classical biological or radiobiological principals are apparently at work in high‐dose SBRT treatments. Supported by the Enid A. Haupt Endowment for Medical Physics
SU‐C‐BRA‐03: SPARK 4DCT ‐ a Simulation, Post‐Processing and Resorting Kit for 4DCTs
Authors: Speier C , Sharp G , Wolfgang J
Published: June 2012

Purpose: 4DCT images can suffer from poor image quality, motion artifacts, and missing data, which sometimes requires rescanning the patient. Most commercially available resorting software do yet not support adequate solutions for the manual correction of scans where a simple phase based resorting algorithm does not yield a satisfying Result: Our purpose is to improve image quality through better resorting tools. Methods: We have developed SPARK 4DCT, a Java based tool that allows the user to choose from six different automatic resorting algorithms, has an advanced manual resorting editor, and interpolates missing data caused by irregular breathing. Expert users can find a direct and convenient access to correcting phase and image selection errors, while advanced automated algorithms improve the baseline quality of the 4DCT with less effort. Results: Using anonymized patient data as examples, we present how the most common problems of 4DCT quality are solved with SPARK 4DCT's alternative resorting algorithms, manual amplitude/phase assignment, missing data interpolation and manual resorting. To prove feasibility for the clinical routine, we also estimate the time required for improving the 4DCT quality. Conclusions: By advancing the workflow of 4DCT resorting and extending the tools available to improve their quality, SPARK 4DCT can replace the commercial resorting software, and is potentially a useful tool to improve the clinical routine of 4DCT resorting in many hospitals. Its design as a Java applet makes its integration into any clinical environment easy, because it allows for access from almost any computer/operating system. As an asset to the 4DCT imaging community the tool will be freely available as an open source code, which, in combination with its simulation capabilities, makes this tool a candidate for facilitating further 4DCT research.
SU‐C‐BRA‐05: Enhancement of Lung Tumors Detectibility during Gantry Rotation Using Iterative Principal Component Analysis Methodology
Authors: Sandhu R , Kim J , Zhang T , Yan D , Zhuang L , Ionascu D
Published: June 2012

Purpose: The purpose of this study is to use an Iterative Principal Component Analysis (PCA) methodology to enhance lung tumor motion relative to stationary surrounding anatomy in order to improve tumor localization and allow efficient lung tumor tracking. Methods: A digital thorax phantom containing several ellipses of different sizes and densities was used to simulate tumor, lungs and vertebral column. The CBCT acquisition numerically generated 700 projections in 2min for 360deg. The projections were simulated using line‐integrals of phantom density with parallel‐beam geometry. The rigid anatomy perspective change remains minimal within 5–6deg while a typical tumor is moving approximately half breathing cycle. A set of 10–12 projection images is generated within 5–6deg arc and used for PCA analysis. PCA transformed the axes of the image set to extract uncorrelated dominant features. For a given set of 10–12 projections, the middle image was filtered using PCA where only a few principal components were considered; satisfying user defined cut‐off threshold. The method is applied to all 700 projections based on a moving‐angle window. The eigenvectors selection criterion allowed different number of components to reconstruct PCA‐filtered images depending on variation among data set. Proposed methodology was evaluated using simple sin, sin6 and complex patient motion profiles. Results: The PCA coefficient cut‐off value of 10% and 20% recovered the amplitude, period and phase of phantom motion within 5% error. These cut‐off values also enhanced lung tumor visibility of PCA‐filtered images. The methodology was also implemented on prerecorded patient CBCT projections. The patient study was evaluated for 10% and 20% cut‐off values. PCA coefficient with 20% cut‐off value provided superior contrast. Conclusion: The iterative principal component analysis is a robust method to emphasize variation among CBCT projection images when rigid anatomy remains relatively stationary. The proposed methodology has shown promising results on the patient data.
SU‐C‐213CD‐01: Automated Marker Tracking for Intra‐Fractional Image Guidance in Radiotherapy
Authors: Wisotzky E , Fast M F , Nill S , Oelfke U
Published: June 2012

Purpose: We have developed two automated methods for real‐time detection of intra‐fractional target motion during treatment with the aid of metallic markers based on ‘in‐line’ acquired x‐ray images. Fast detection algorithms are desirable to facilitate tumor tracking applications. Methods: A Siemens linac was equipped with a 16×16″ a‐Si flat panel detector (FPD) underneath the treatment head. A diagnostic x‐ray tube was positioned opposite to the treatment head; geometrically separating MV treatment and kV imaging fields on the FPD. We analyzed x‐ray images of a lung phantom equipped with a marker for better contrast. For the automated marker detection we developed two algorithms as part of our image acquisition application. Both algorithms are based on gray‐value template matching with normalized cross‐correlation (NCC). One of the algorithms pre‐ calculates suitable candidate regions by employing a canny edge detection filter. In this study, we wanted to a) study the quality of template matching under the influence of MV induced image artifacts (e.g. stripe artifacts), and b) investigate if pre‐selection of candidate regions leads to reliable marker detection. Results: Our lung‐phantom study has demonstrated that matching a 21×21 pixel template over an 81×81 image with NCC takes about 9.9+−4.5 ms. This method is very reliable and works for a wide dose range. Using canny pre‐filtering reduces the latency to 1.1+−0.7 ms, but marker detection becomes less reliable at our lowest dose level (0.6 mAs). In the presence of an 8×8 cm̂2 MV field, the latencies remain unchanged but the correlation factors decrease sharply by up to 22%. We observed that MV induced stripe artifacts overlapping with the marker are the greatest hurdle to successful detection. Conclusions: While template‐matching over the entire image reliably finds the correct marker position, it is possible to accelerate the search for high contrast images with the help of canny filtering. Supported by Siemens Healthcare/CR.
SU‐C‐213CD‐04: Evaluation of IsoCal Imaging Isocenter Calibration System for Varian OBI Machines
Authors: Gao S , Du W , Balter P
Published: June 2012

Purpose: To evaluate the accuracy and reproducibility of the IsoCal geometric calibration system for Varian OBI kV and EPID imaging systems. Methods: IsoCal consists of hardware (IsoCal phantom, collimator plate) and software. IsoCal calibration starts by imaging the phantom and collimator plate using MV images with different collimator angles as well as MV and kV images at different gantry angles. The software then identifies objects on collimator plate and in the phantom to determine the location of the treatment isocenter and its relation to MV/kV imaging centers. It calculates offsets of the position of the imaging panels versus the treatment isocenter as function of gantry angle and writes a correction file that can be applied to MV/kV system to correct for offsets in the position of the panels. We performed IsoCal calibration three times in a row on 5 different linacs, each time with an independent setup. We also compared the IsoCal calibrations with an in‐house Winston‐Lutz‐based (WL) system as well as a Varian cube‐based (VC) system. Results: The IsoCal corrections ranged from 1.1 to 2.3 mm for MV and 1.1 to 1.8 mm for kV imagers across the 5 linacs. The variations in the three calibrations for each linac were within ±0.2 mm. The differences between IsoCal and the WL and VC systems were within 0.5 mm and 1.0 mm respectively. Without IsoCal the WL results showed discrepancies between the treatment isocenter and MV/kV imaging center ranging from 0.9 to 1.6 mm (MV) and 0.5 to 1.1 mm (kV), with IsoCal applied they were reduced to 0.2 to 0.4 mm (MV) and 0.3 to 0.4 mm (kV) across the 5 linacs. Conclusions: This study demonstrates that IsoCal is an accurate and consistent method for MV/kV image system calibration and periodic quality assurance.
SU‐C‐213CD‐05: Respiratory Signal Triggered 4D Cone‐Beam Computed Tomography on a Linear Accelerator
Authors: Cooper B , O'Brien R , Keall P
Published: June 2012

Purpose: To compare imaging dose and image quality for a commercially available 4D CBCT system and a proposed respiratory signal triggered 4D CBCT system which uses fewer projections and thus can reduce imaging dose burden. Methods: A large original set of full‐fan kilovoltage projection images of a stationary thorax phantom was acquired through 200 degrees of gantry rotation. This dataset was reconstructed to produce a ‘ground truth’ CBCT dataset (GT). Using acquisition parameters from a commercially available 4D CBCT system, the original projections were resampled to produce a 4D CBCT dataset (A). A sine wave respiratory signal, with period 4 seconds, is assumed and used to split projections into phase bins. Respiratory signal triggered 4D CBCT uses the same acquisition parameters, but the respiratory signal is used to trigger projection acquisition so that only one projection per phase bin is acquired (dataset B). For the commercial 4D CBCT system (A) and the respiratory signal triggered 4D CBCT system (B), image quality was quantified using the root mean squared deviation (RMSD) of the pixel values from the ground truth (GT) dataset. Imaging dose was assessed assuming one projection equals one dose unit. Results: The imaging dose for 4D CBCT system (A) was 118 dose units compared to the proposed 4D CBCT system (B) 58 dose units. The RMSD was calculated as 105.4, std. dev. 5.4 and 107.5, std. dev. 4.0 for the 4D CBCT system (A) and the proposed 4D CBCT system (B) respectively. Conclusions: The respiratory signal triggered 4D CBCT system exhibits a significantly reduced dose compared to the commercial 4D CBCT system. This comes at a small reduction in image quality. Future work will be to investigate the performance of the proposed 4D CBCT system with real respiratory signals. This work has been partially funded by the National Health and Medical Research Council, Australia (funding application ID APP1034060).
SU‐C‐217BCD‐06: Analysis of Different CT Accreditation Programs
Authors: Goodenough D
Published: June 2012

Purpose: This study will review two alternate pathways for CT accreditation ‐ the program of the American College of Radiology (ACR) and the program of Intersocietal Accreditation Commission (IAC). The study will compare and contrast the two programs. Methods: The requirements of the ACR‐CT accreditation and IAC ‐ICACTL programs are reviewed for both the clinical and technical aspect. Physics data collected on several multidetector CT scanners (MDCT), including 16, 64, 128, 320, and up to 750 detector arrays utilizing both the ACR CT phantom and the CATPHAN 600 CT Phantom (note, IAC does not require a specific phantom, thus this widely used commercial phantom) is used. Scanning protocols are based on the protocols as required by ACR or IAC. Data necessary to complete the data forms for alignment, CT# accuracy, slice width, low contrast resolution (uniformity and noise, distance accuracy and high contrast spatial resolution), obtained measurements were made as specified in the accrediting group's instructions using manual processes as well as automated analysis approaches. Results: The results show examples of significant differences in the required levels of physical performance of head and body scanning under the different programs, particularly in the high resolution modulation transfer function (MTF) scanning ability. Likewise, significant differences in clinical body scanning ability of approved devices are shown. Conclusions: Significant differences in the levels of CT performance required to pass the two different accreditation programs are shown. The data sets indicate that a single phantom requirement for an accreditation program is unnecessary because the portability of physics data should obviate the need to purchase duplicate phantoms for accreditations purposes, and allow for more ready comparison between accreditation programs, government and industry specifications. This paper may guide imaging professionals in decisions regarding accreditation pathways with CT.DJG serves as a consultant to The Phantom Labratory and Image OWL, Salem, NY
SU‐C‐217A‐02: An Effective Dose Monitoring Program for Computed Radiography
Authors: Johnson J , Samei E , Christianson O , Bower D
Published: June 2012

Purpose: To develop a method for determining the effective dose to patients undergoing computed radiography examinations and incorporating this method into an automated dose monitoring program. Methods: Images from computed radiography exams were pulled from PACS to get dicom header information. Exposure indicator values were converted to plate exposure using vendor specified relationships between exposure indicator and plate exposure. Plate exposure was converted to patient entrance skin exposure through experimentally determined transmission factors. Transmission factors were determined by placing an ion chamber 40 inches from the x‐ray source with a grid directly in front of the ion chamber and lucite directly in front of the grid. This was repeated for different lucite thickness (15.7cm, 20.3cm, 24.7cm, 30.3cm, and 34.5cm), kVp (60, 80, 100, 120), field size (5×5, 10×10, and 14×14 in.), and grid ratio (none, 8:1, and 12:1). These data were fit to a surface using the following equation for each grid ratio and field size: TF=(C1*‐kVp—̂2+C2*kVp+C0)*ê(−C4*thickness) This equation was used to calculate transmission factors for patient exams using assumed kVp and thickness. Patient entrance skin exposure was converted to effective dose through Monte Carlo simulations through PCXMC using kVp and patient thickness typical of each exam for average adults. Results: Examination of patient dose for different scans shows wide variability in the amount of radiation dose delivered to patients. For Chest exams, the dose range was from 0.002mSv to 0.3 mSv with a median dose of 0.044mSv. Philips had a median dose of 0.05 1mSv while Carestream had a median dose of 0.033mSv. Conclusions: The results emphasize the importance of monitoring dose for computed radiography. This data can be used to compare dose across vendors, machines, and exam types. We can determine diagnostic reference levels, flag outliers, and potentially optimize image quality.