bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐F‐110‐07: Comparison of S Values for Three Classes of Adult Computational Phantoms for I‐131 in the Thyroid
Authors: Lamart S , Melo D , Bouville A , Simon S , Eckerman K , Lee C
Published: November 2011

Purpose: To compare S values for three classes of adult computational phantoms for Iodine‐131 in the thyroid. Methods: S values between the thyroid (source organ) containing I‐131 and important target organs were compared for three classes of computational human phantoms: stylized (mathematical), voxel and hybrid. S values were calculated for International Commission on Radiological Protection (ICRP) reference adult voxel phantoms and the University of Florida (UF) adult hybrid phantoms by using the Monte Carlo transport code MCNPX2.5, and compared with S values derived 30 years ago at the Oak Ridge National Laboratory (ORNL) for their stylized phantom but using a different transport code. Eleven target organs were selected for comparison: brain, breast, stomach wall, small intestine wall, colon wall, heart wall, pancreas, salivary glands, thyroid, lungs, and active marrow. We also computed and compared specific absorbed fractions (SAF) and chord length distributions (CLD) among the phantoms for source and target organ‐pairs. Results: Our analysis showed on average, an underestimation of S values and, consequently, of organ doses for the ORNL stylized phantoms compared to the ICRP and UF phantoms. Inter‐organ distance and organ shape differences were identified as the main cause of the differences. Conclusions: The ICRP and UF phantoms are considered to more realistically model the human anatomy than the ORNL stylized phantoms. Therefore, the S value differences likely arise from unrealistic locations and shapes of the thyroid and target organs in the stylized phantoms. In addition, the S value differences between ICRP and UF phantoms illustrate there can be differences among phantoms designed to match the ICRP reference anatomy data, which suggests that human variability has not yet been fully described. This comparison indicates the value of the newer generation phantoms for conducting more reliable internal dosimetry.
MO‐G‐BRB‐02: Commissioning a Small Animal Irradiator Using 2D and 3D Dosimetry Techniques
Authors: Newton J , Oldham M , Li Y , Adamovics J , Das S
Published: November 2011

Purpose: To commission and characterize a novel small animal irradiator, the XRad225cx from Precision X‐Ray Inc. This system is capable of delivering both square and circular fields ranging in size from 1mm to 40mm. The combination of very small field size and relatively low energy (225kV) represents a substantial challenge in acquiring accurate dosimetry beam data. This work reports on commissioning studies using 2 independent dosimetry systems: EBT2 radiochromic film and PRESAGETM /optical‐CT 3D dosimetry. Methods: Initial measurements were made with 6×8cm pieces of EBT2 radiochromic film. Output factors were determined at 3 depths (0, 0.5 and 2cm) from films irradiated normally resting on the surface or sandwiched in solid water. Percent‐depth‐dose (PDD) measurements were made from films also sandwiched in solid water and irradiated edge on. Independent 3D dosimetry measurements were obtained using PRESAGETM radiochromic dosimeters and imaged with the Duke Large field‐of‐view Optical‐CT Scanner (DLOS). Output factors and PDDˈs were obtained using a combination of small fields. Results: The relative output factors and PDDˈs obtained from EBT2 and PRESAGETM showed agreement below 1 cm depth. For field sizes >1cm, relative output factors were found to be stable (∼1.00) with differences between PRESAGETM and EBT2 <6%. At smaller field sizes the output relative to the 20 mm cone decreased substantially, down to ∼0.5 for the smallest 1 mm cone. A slightly greater drop was observed in the PRESAGETM measurements, which is currently being investigated. Conclusions: Output factors and PDD curves were successfully obtained for all cones using a combination of EBT2 and PRESAGETM. Consistency was observed between both independent measurements after correcting for the lack of exact water equivalence of both the solid water and PRESAGETM. The 3D dosimetry system has potential advantages in terms of convenience, efficiency and comprehensiveness when commissioning small fields.

Funded by NIH R01CA100835 and NIH S10‐3034539
MO‐G‐BRB‐06: Integrating Carbon Nanotube and Micropallet Technologies for Microbeam Radiotherapy Biology Research
Authors: Wang S , Fiordalisi J , Xu W , Zhang J , Snider J , Yang G , Cox A , Allbritton N , Chang S
Published: November 2011

Purpose: Microbeam radiotherapy (MRT) is a preclinical therapy that has been shown in animal experiments to have a selective ability to eradicate tumor cells while sparing normal tissue. However, potential MRT clinical application is hindered by the lack of understanding of the biological mechanisms involved. To study DNA damage and repair mechanisms and cell survival under MRT irradiation, our objective is to integrate a carbon nanotube field emission technology‐enabled high dose rate (100ˈs Gy/s) electron microbeam with a micropallet array technology‐enabled cell retrieval and analysis system. The focus of this presentation is a feasibility demonstration of the integrated system for MRT cellular irradiation. Methods: We have upgraded our carbon nanotube field emission‐based prototype cell irradiator system to produce a single or multiple ∼40 micron wide electron MRT beams at a dose rate range of several hundred Gy per second. Dosimetry is measured using GAFCHROMIC HD‐810 film. SW480 colon cancer cells are plated on individual square micropallets of 60 or 100 micron in size, placed in a customized culture dish. Cells can be collected from each individual micropallet while remaining adherent to their growth surface for further analysis. Results: We have demonstrated the MRT cellular irradiation using gamma‐H2AX, a nuclear histone protein that becomes phosphorylated in proximity to IR‐induced DNA double strand breaks. The MRT radiation beam profile shown by staining fixed cells post‐ IR for phospho‐H2AX was consistent with calculation. Conclusions: We have developed an integrated MRT cellular irradiation and analysis system using carbon nanotube field emission technology and micropallet array technology. We have characterized the dosimetry and demonstrated the feasibility of MRT beam irradiation in cellular irradiation for future mechanistic research on microbeam therapy.

Acknowledgements: This work is partially supported by North Carolina University Cancer Research Fund.
MO‐G‐BRC‐02: Patient Specific Out‐Of‐Field Dose Calculation Tool for 6MV and 18MV: Development and Validation
Authors: Randeniya S , Mirkovic D , Kry S , Titt U , Newhauser W , Howell R
Published: November 2011

Purpose: A factor that greatly limits the use of Monte Carlo methods for patient specific dose calculations in research is the substantial amount of effort required to define the Monte Carlo geometry of the actual treatment and patient setup. The purpose of this study was to develop and validate computational infrastructure to automatically convert radiation field parameters and computed tomography (CT) data from Digital Imaging and Communications (DICOM)format to Monte Carlo input format, and automate a Monte Carlo based dose calculation system for external beam photon radiation therapy. Methods: Computational infrastructure was developed using DCMTK, the DICOM tool kit. The dose calculation system (ADCS) was automated using a shell script. For validation of the ADCS, infield doses calculated by the ADCS were compared with those calculated by the treatment planning software using an eight‐field, 6 MV, step‐and‐shoot intensity modulated radiation therapy plan. Doses were calculated in a water phantom, and an anthropomorphic phantom based on CT data. Results: For each field, more than 95% of the dose voxels passed 3% and 3‐mm criteria of gamma‐index analysis of 3‐D dose distributions in the water phantom. The central axis depth dose curve agreed with in 15% (1stardard deviation) to the TPS calculations in the anthropomorphic phantom for a single representative field of the RT plan. Conclusions: The ADCS can accurately extract patient‐specific radiation treatment parameters and automatically incorporate them into the Monte Carlo format and create final dose distributions compatible with commercial treatment planning systems. This automated calculation infrastructure reduces the time required to define the Monte Carlo geometry and potential for human error. This system is capable of automating and calculating doses for conventional radiation therapy and 18MV. It is also capable of calculating out‐of‐field doses (region of interest in patient anatomy can be selected prior to running ADCS).
TU‐A‐BRB‐04: Incorporating Beam‐Specific Target Volumes Into Beam Angle Selection in Proton Therapy
Authors: Park P , Zhu X , Sahoo N , Lee A , Zhang L , Cheung J , Dong L
Published: November 2011

Purpose: Due to range uncertainty and its interplay effect with setup error and internal tissue heterogeneity, proton beams usually use a large distal and proximal margin, especially when the distal margin falls in a low density tissue, such as lung. As a result, beam angle selection is very important for proton therapy. In this study, we incorporate beam‐specific planning target volumes (bsPTVs) into a beam angle optimization process to minimize required treatment volumes for each beam and combination of two beams along with other dose restrictions to the organ at risks (OARs) in the beam path. Methods: The bsPTVs were constructed for each beam angle over 10 degrees interval by taking into account both the range and setup error. Subsequently, doses from each beam angle were approximated using analytical dose model assuming uniform‐dose distribution throughout the target volume. The objectives set included the volume of bsPTV for each beam, the volume of intersection between multiple bsPTVs, and mean doses to OARs in the beam path. Results: A software tool was developed and applied to optimize two‐beam arrangement for a lung cancer patient. Objectives were plotted as figure‐of‐merits in color maps and bsPTVs were overlaid on axial CT images to assist the interpretation of results and the eventual angle selection. Conclusions: We found that the intersection of beam‐specific PTV is a convenient tool for minimizing the combined high dose volume by selecting the best combination of beam angles. Our visual tools that display trade‐offs between different objectives were found helpful for angle selection as well as the interpretation of results.

Supported in part by NCI P01 CA021239
TU‐A‐BRB‐09: A Full Precision Large‐Scale Beam Angle Selection Framework
Authors: Bangert M , Ziegenhein P , Oelfke U
Published: November 2011

Purpose: We present a full precision large‐scale beam angle selection (BAS) framework for IMRT treatment planning. It is developed to assess the clinical impact of different BAS strategies. Methods: For more than 400 candidate beam directions, full precision dose calculations are performed on computed tomography data at a 2.62×2.62×2.62 mm3 resolution. The resulting 20–50 GB of dose influence data are distributed on a high performance computer cluster with 10 nodes featuring 12 CPUs each. On this architecture, we can instantaneously combine any subset of candidate beams to a treatment plan. Exploiting parallel programming techniques, we perform full‐fledged beamlet weight optimizations by minimization of a quadratic objective function in about three seconds per treatment plan. In first studies, we 1. derived explicit visualizations of the solution space of the BAS problem, and 2. compared a BAS heuristic with an iterative strategy, a genetic algorithm, and simulated annealing. Results: 1. For three intracranial cases, treatment plans featuring five beams were investigated. Three beams were fixed at 0°, 120°, and 240°. The remaining two beams were varied in 5° increments yielding 2628 treatment plans. The resulting objective function landscapes are descriptive visualizations of the nonconvexity of the BAS problem. 2. In comparison to standard beam configurations, the genetic algorithm, the iterative strategy and simulated annealing yielded improved treatment plans with a reduced number of beams for three intracranial cases. The genetic algorithm exhibited the best convergence properties. The heuristic BAS strategy also provided beneficial treatment plans at a lower computational cost. Conclusions: We developed a powerful tool to compare different BAS strategies. We confirmed the non‐convex nature of the BAS problem and showed that genetic algorithms outperform simulated annealing and iterative strategies for our implementations. We demonstrated that smart BAS heuristics may be a valuable alternative for clinical application.
TU‐A‐BRC‐01: Tumor Perfusion Topography Pattern Correlated with Primary Failure in Cervical Cancer Radiotherapy
Authors: Zhang D , Mayr N , Lo S , Yuh W
Published: November 2011

Purpose: Tumor perfusion assessments with dynamic contrast enhanced (DCE) MRI have been focused on the overall degree of low DCE in tumors, without considering the characteristic geographic distribution of the perfusion pattern within the tumor. This study was to investigate the topographic and temporal perfusion patterns of cervical cancer and correlate them with treatment failure. Methods: 101 cervical cancer patients were treated with external beam radiation therapy (RT), concurrent chemotherapy, and brachytherapy. The patients underwent serial DCE‐MRI prior to RT start, in early‐RT (at 20–25 Gy), and in mid‐RT (at 45–50 Gy). The center slice of the tumor ROI was selected to find the number of pixels with signal intensity (SI) local maximum within the ROI (Num_max). After further separation of the ROI into central zone and peripheral zone, Num_max was divided into two terms Num_max_C (for central zone) and Num_max_P (for peripheral zone). The 3 parameters for tumor pixel SI local maximum (Num_max, Num_max_C, Num_max_P) were compared, and correlated with local control and patient survival. Results: More pixels with SI local maximum dwell in the peripheral zone of the tumor ROI than in the central zone (Num_max_P > Num_max_C). At pre‐RT, both Num_max and Num_max_P correlate with local tumor control (p= 0.029, 0.005 respectively), and with disease‐specific survival (p= 0.012, 0.007 respectively). But the central zone Num_max_C does not correlate with local control or survival. Similar results remain in early‐RT and mid‐RT DCE‐MRI study of tumor SI local maximum patterns. Conclusions: This preliminary study suggests that tumor perfusion micro topography features revealed by DCE‐MRI influences tumor primary dose response, on which the tumor peripheral region is more relevant than the central region. This could potentially impact on the treatment plan design. And the predictive micro topography features can be detected even before the treatment starts.
TU‐A‐BRC‐04: Quantifying the Predictive Power of Multiparametric PET Imaging in a Prospective Veterinary Dose Escalation Trial through Voxel Regression
Authors: Bowen S , Chappell R , Bentzen S , Deveau M , Forrest L , Jeraj R
Published: November 2011

Purpose: Statistical tools to derive imaging‐based prescription functions linked to outcome data have great potential for dose painting. The predictive power of PET images was assessed in a veterinary dose escalation trial via voxel regression.Methods: Ten canine patients with sinonasal tumors underwent pre‐treatment PET/CT scans of [F‐18]FDG, [F‐18]FLT and [Cu‐61]Cu‐ATSM (PETpre). Following radiotherapy, nine patients underwent FDG PET/CT scans at three months (FDGpost). Multivariate voxel‐based regression of PETpre images to the FDGpost image, a surrogate of local recurrence, was performed in each patient for linear, log‐linear, log‐ ratio and generalized‐linear models. Model predictions of patient FDGpost images were assessed by the coefficient of determination R‐squared. Population predictive power was established for non‐zero regression coefficients using one‐sample t‐tests, as well as for different coefficients between RECIST‐classified responders and non‐responders using two‐ sample t‐tests. Results: The log‐ratio model achieved the best patient model fits (mean: R‐squared=0.64, range: [0.22–0.85]). The population predictive power of FDGpre to FDGpost was statistically significant in all but the log‐ linear model (p=0.12 vs. p<0.03). The linear model classified the slope of 0.37 for RECIST non‐responders to be different from the slope of 0.07 for RECIST responders (p=0.01). The generalized‐linear model related FDGpre to FDGpost by a linear power law (coefficient = 0.93, p<0.01). FLTpre and Cu‐ATSMpre had non‐significant coefficients, though Cu‐ATSMpre weakly classified RECIST response in the generalized‐linear model (non‐ responders: coefficient = 0.68; responders: coefficient = −0.22; p=0.12). Conclusions: Results from the majority of regression models indicate that pre‐treatment FDG is an independent predictor of three month post‐ treatment FDG. The log‐ratio model of relative PET uptake produced the best patient fits. The generalized‐linear model characterized pre‐treatment Cu‐ATSM as a potential classifier of RECIST response. Further statistical analysis of the possible synergistic interactions between image parameters and radiation dose may lead to the discovery of a dose painting prescription function.
TU‐A‐BRC‐06: Using Hyperpolarized 13C Magnetic Resonance Spectroscopy to Detect Radiation Induced Lung Injury at an Early Stage
Authors: Thind K , Ouriadov A , Feiesen‐Waldner L , Chen A , Scholl T , Fox M , Wong E , VanDyk J , Hill R , Hope A , Santyr G
Published: November 2011

Purpose: To use hyperpolarized, 13C Magnetic Resonance Spectroscopy for early detection of Radiation Induced Lung Injury (RILI) by quantifying the ratio between metabolites of, 13C‐lactate and, 13C‐pyruvateMethods: Rats were irradiated with dose of 14 Gy to the thorax region to induced RILI using a, 13Co source. The contrast agent,, 13C‐pyruvate was hyperpolarized using Dynamic Nuclear Polarization (DNP) that increases signal intensity by four orders of magnitude. It was injected into the animals two weeks post irradiation and dynamic, 13C‐spectroscopy was performed. Proton Images were acquires prior to the spectroscopy for proper localization of the thorax region. Results: A factor of more than two increase in the,13C‐lactate to,13C‐ pyruvate ratio was observed for the irradiated rats compared to the normal animals. This result supports the hypothesis that an increase in production of lactate is evident with onset of hypoxia, which is a consequence of RILI. Conclusions: Significantly higher ratio of, 13C‐lactate to, 13C‐pyruvate is seen the irradiated animals compared to the normal animals demonstrating the feasibility of using, 13C pyruvate to probe in in vivo metabolism and its use as an early market for onset of RILI.
TU‐C‐220‐07: Photoacoustic and Ultrasound Imaging Using a Hemispherical Aperture
Authors: Kruger R , Lam R , Reinecke D , DelRio S
Published: November 2011

Purpose: The aim of our research is to develop a breast cancer screening alternative to x‐ray mammography that will improve screening accuracy in women with dense breasts and young women with a predisposition to breast cancer. Methods: We have implemented 3D photoacoustic and ultrasound computed tomography using a single transducer array that samples a hemispherical aperture. Such an array samples radial projections though K space uniformly and can produce 3D images that demonstrate nearly isotropic spatial resolution for both photoacoustic and backscattered ultrasound. Data acquisition and image reconstruction strategies will be discussed. Results: We have successfully visualized hemoglobin distribution in the breast vasculature of a normal patient. Spatial resolution was better than 0.5 mm and vessels were adequately visualized to a depth of 35 – 40 mm. Microcalcifications as small as 180 microns were visualized in 3D in a breast‐tissue‐mimicking phantom. Conclusion: Hemoglobin and microcalcifications can be imaged in 3D using a single ultrasound detector array that samples a hemispherical aperture. Application of the technology for detecting two biomarkers associated with breast cancer — hemoglobin and microcalcifications ‐ will be discussed.

Educational Objectives:

1. Introduce the concept of photoacoustic imaging using ultrasound transducer arrays.

2. Discuss data acquisition strategies and reconstruction strategies.

3. Discuss photoacoustic contrast mechanisms
TU‐E‐110‐02: Multibeam X‐Ray Source Array Based on Carbon Nanotube Field Emission
Authors: Zhou O , Lu J , Calderon‐Colon X , Qian X , Yang G , Cao G , Gidcumb E , Tucker A , Shan J , Spronk D , Sprenger F
Published: November 2011

Purpose: We recently demonstrated the feasibility of generating high current and high energy x‐ray radiation using field emitted electrons from the carbon nanotubes (CNTs). The purpose of the present work is to develop a spatially distributed multiple beam x‐ray array technology for stationary tomography imaging, including digital breast tomosynthesis, with the goal of increasing the spatial resolution and scanning speed. Method and Materials: CNT cathodes fabricated by patterned electrophoretic deposition were used as the field emission electron source for x‐ray generation. Computer simulations and experimental measurements were carried out to design the electrostatic lens to focus the field emitted electrons to the predetermined area on the metal anode. Finite element analysis was performed to determine the anode heat load under the desired operation conditions. Spatially distributed x‐ray source arrays with one‐ and two‐dimensionally distributed focal spots were constructed using matrix addressable multi‐pixel CNT cathode, and corresponding focusing and anode structures. By varying the extraction electrical field, x‐ray radiation with programmable waveform was readily generated which can be gated with external triggers such as physiological signals with sub‐microsecond response time. Dedicated control electronics were designed and manufactured to switch, scan, and regulate the x‐ray beams. Results: Several spatially distributed field emission x‐ray source arrays with different configurations and performance parameters have been fabricated and characterized for different imaging systems. Stable operation at anode voltage up to 160kVp has been achieved. Through improvement of the CNT cathode and electronic regulation beam‐to‐beam consistency in intensity and focal spot size has been demonstrated. A dedicated x‐ray source array has been designed and fabricated for stationary digital breast tomosynthesis. The source comprises 31 individually controllable x‐ray beams covering 30 degrees viewing angle, allowing collection of the all the projection images from different angles without any mechanical motion blur. It is operated up to 50KVp anode voltage at an effective focal size comparable to that of the traditional mammography tube. Tomosynthesis images of a breast phantom were obtained using the new source array and a flat‐panel x‐ray detector. Conclusion: The distributed field emission x‐ray source array technology offers unique capabilities that are attractive for tomography imaging and potentially for radiotherapy. The flexibility in source configuration opens up new possibilities in system design.

Conflict of Interest: Zhou is a board director of XinRay Systems which develops and commercializes the CNT X‐Ray source technology.
TU‐G‐BRA‐01: Clinical Significance of RBE Variations in Proton and Carbon Ion Therapy (an Overview/introduction to the Problem)
Authors: Paganetti H , Grassberger C , Carabe‐Fernandez A
Published: November 2011

The relative biological effectiveness (RBE) is defined as the ratio of the doses required by two radiations to cause the same level of effect. Thus, the RBE needs to be considered if dose constraints from photon therapy are to be adopted.

Proton therapy has been based on the use of a generic RBE of 1.1, which is applied to all treatments independent of dose/fraction, position in the irradiated volume, beam energy or the tissue. Quantitative dependencies of the RBE on various physical and biological properties are disregarded. The variability of RBE in clinical situations is believed to be within 10%. Elevated RBE values might be expected particularly near the edges of the high‐dose volume because doses may be deposited by high‐LET particles. Furthermore, the increase in RBE as a function of depth in the patient results in an extension of the bio‐effective range of the beam, which is being considered in treatment planning.

The magnitude of RBE values and their variations is significantly larger in Carbon ion therapy than in proton therapy. Heavy ions have a potential advantage compared to protons when it comes to their therapeutic ratio due to an elevated RBE in the tumor (based on the oxygen enhancement ratio and higher average LET values) compared to the surrounding tissue. However, there are considerable variations in RBE within the irradiated volume that have to be considered in treatment planning and delivery.

At present there are still considerable uncertainties in RBE values and their dependencies on dose, LET, and alpha/beta ratio. This presentation will illustrate the magnitude of RBE variations in proton and Carbon beams. Furthermore, it will demonstrate the clinical significance for proton therapy treatments involving tissues with low alpha/beta ratio and show a method for biologically optimized treatment planning in proton therapy.
TU‐G‐BRA‐05: Optimization of Normal Tissue Sparing through Ion Selection
Authors: Remmes N , Herman M , Kruse J
Published: November 2011

The variable radiobiological effect (RBE) of heavier ions like carbon make it challenging to compare dose distributions across different ions. Comparisons must be made between the isoeffective dose, the product of the dose with the RBE, requiring the use of a model that can predict how RBE changes across different ions. This presentation will discuss Geant4 simulations of parallel opposed beams of protons, helium, lithium, beryllium, carbon, and neon ions incorporating a microdosimetric model of RBE. The beams are constructed to give a homogeneous isoeffective dose to a treatment volume in the center of a water phantom for tissues covering a range of cobalt equivalent alpha/beta ratios from 1 to 20 Gy. Normal tissue isoeffective doses are then compared for different ions across the range of normal tissue and target tissue radiosensitivities. The ion type yielding the optimal normal tissue sparing is found to be highly dependent on the alpha/beta ratio of both the normal and target tissue. For instance, the calculated isoeffective dose to normal tissue at a 5 cm depth varies by almost a factor of 5 for carbon ions, ranging from a factor of 2 less than the isoeffective dose of a similar proton treatment to a factor of 2 greater. The heavier ions such as carbon are superior in cases where the alpha/beta of the target tissue is low and the alpha/beta normal tissue is high. However, lighter ions such as lithium and beryllium appear to offer dose advantages similar to carbon but with considerably less normal tissue dose when the alpha/beta in the target tissue is high and the alpha/beta in the normal tissue is low.

Learning objectives

1. To understand the variation of isoeffective doses to normal tissues across ion types for a simple parallel opposed treatment.

2. To understand the dependency of isoeffective doses to normal tissues on the combination of both normal tissue radiosensitivity and target tissue radiosensitivity.
TU‐G‐BRB‐02: Comprehensive Handling of Time‐Dependent Quantities in Scanning Beam Simulation
Authors: Shin J , Perl J , Schümann J , Paganetti H , Faddegon B
Published: November 2011

Purpose: To provide a comprehensive and flexible method for handling time dependent quantities including interplay effects in proton beam scanning. Methods: The time feature was devised to handle time‐dependent quantities in the Monte Carlo simulation. Each time‐dependent quantity corresponds to one time feature. A time feature can be expressed as a simple mathematical function or composed of more complex, pre‐defined functions. The functions may be combined concurrently and/or consecutively so that users can customize complex time features. During simulation, time is set in one of two manners: 1. Randomly chosen time, suitable for handling continuous behaviors, or 2. sequentially‐generated time, where time interval is equally divided. This time feature has been incorporated in TOPAS, a tool for particle simulation with Geant4, under development to make Monte Carlo simulation more accessible to both clinical and research physicists. Results: The time feature has been deployed to simulate various proton beam scanning patterns in clinical proton beam nozzle. The patterns include parallel, raster, circular, saw‐tooth, and Lissajous figure scans. Through the parameter management in TOPAS, time features for those scanning patterns were easily implemented. Dynamics of the beam including pulse shape, spot size, and movement were concurrently simulated. Randomly set time gave more accurate results when fewer histories were simulated, resulting in under‐sampling when time was set sequentially, while the simulation time with the 2 methods was similar for the same number of histories. Conclusions: Methodology has been developed to comprehensively describe time dependent behaviors in the Monte Carlo simulation and was assessed by applying to clinical proton beam scanning. A novel aspect of the method of separation of the time generators and time receivers has made it straightforward to handle multi time‐ dependent quantities and is therefore relevant to fully simulate interplay effects.

The project described was supported by Award Number R01CA140735 (“PBeam: A Fast and Easy to Use Monte Carlo System for Proton Therapy”) from the National Cancer Institute.
TU‐G‐BRB‐04: Optimal Frequency of CT Imaging for Monitoring Target Volume and Estimating Delivered Dose in Standard and Hypofractionated Prostate Proton Therapy
Authors: Wang Yi , Efstathiou Jason A. , Lu Hsiao‐Ming , Sharp Gregory C. , Trofimov Alexei V.
Published: November 2011

Purpose: To evaluate the uncertainty in dose delivery resulted from inter‐fractional organ motion in standard and hypofractionated prostate proton therapy, to assess the need for motion reduction to limit dose deviations in hypofractionated delivery, and to estimate optimal CT imaging frequency for target volume monitoring and accurate dose verification. Methods: We used serial CT images acquired at simulation and daily treatment for ten prostate patients. For each patient, a 3D conformal proton plan (78 Gy, 39 fractions) was created and renormalized for hypofractionated delivery (28, 20, 12 and 5 fractions). The plan was computed on each daily CT. The fractional dose was mapped to the simulation anatomy via deformable registration, with the mapped coverage validated against manual contours. The accurately registered fractions were used to examine whether the target and organ dose accumulated in the various deliveries remained within tolerance, and to evaluate the maximum deviations in dose estimation as a function of imaging frequency. Results: Three patients had more than 33 accurate fractions, and the other seven had at least ten. Without large rectal gas (causing inaccurate registration and large dose deviations), the accumulated target and organ dose remained within limit for delivery in 39 and 28 fractions. For delivery in 20 and fewer fractions, motion reduction would be needed to maintain target coverage and organ sparing. Ten CT scans were sufficient to detect large, systematic changes of prostate volume. To limit the uncertainty in estimated target coverage (V78Gy) to 3%, and rectal dose (both V75Gy and V70Gy) to 5%, ten scans were also sufficient, unless a significant change of prostate volume was observed. Conclusions: For delivery in 39, 28 and 20 fractions, the minimum recommended imaging frequency is one for every four, three and two fractions, respectively. Daily imaging is needed for delivery in 12 and 5 fractions.

This study was supported by the Federal Share of program income earned by Massachusetts General Hospital on C06‐CA059267, Proton Therapy Research and Treatment Center.
TU‐G‐BRB‐06: Conversion of X‐Ray Sinogram to Proton Sinogram to Address the Limited‐Range Issue in Proton Computed Tomography
Authors: Wang D , Mackie T , Tome W
Published: November 2011

Purpose: To investigate a novel methodology of converting x‐ray sinograms into proton sinogram, which can be used to replace the missing part of an actual proton sinogram due to the limited‐range problem. Methods: Modeling has shown that there exist correlations between proton projection and multispectral x‐ray projection for materials in the human body. Based on these correlations, materials can be categorized into: A) adipose tissue, B) non‐adipose soft tissue, C) bone. These three categories can be identified on a regular x‐ray computed tomography (xCT) image without much effort. With an xCT image and its sinogram available, the x‐ray sinogram can be converted to the corresponding proton sinogram by: 1) converting the x‐ray raysum through adipose and non‐adipose soft tissues using the predetermined relationships and the relative portions of two types of material along the ray; and 2) by correcting for bone if the ray passes through it. In a proof‐of‐principle study, numerical simulations were done. The converted proton sinogram was compared to the simulated one. The converted proton sinogram is used to make up the 200 MeV proton projections through water‐equivalent depth (WED) larger than 20 cm, which are then combined with simulated proton projections through WED < 20 cm for pCT stopping power reconstruction. Results: A sinogram profile for view angle = 0 showed the converted projections had a mean error of −0.13% (standard deviation 1.7%), RMS error of 0.20%, compared to the simulated one. The pCT stopping power image reconstructed using the sinogram with converted part (13.5% of total projections) showed a mean error of only +0.3% (standard deviation 4.6%). Conclusions: The proposed methodology allows one to convert x‐ray sinograms into proton sinograms with a reasonable accuracy, and is particularly useful to address the limited‐range problem of pCT scanning.
TU‐G‐BRC‐02: Predictive Tracking for Real‐Time Deformable Motion Using a Dynamic Virtual Patient Model
Authors: Guo B , Xu X , Shi C
Published: November 2011

Purpose: To develop a novel tracking technique for intensity modulated radiation therapy (IMRT) based on dynamic virtual patient modeling. Method and Materials: Predictive tracking uses a dynamic virtual patient model to account for the three‐dimensional deformable motion of the target during realistic IMRT deliveries. The virtual patient model was developed based on the 4DCT images and the structure contours delineated on different respiratory phases. With a real‐time breathing curve, the virtual patient model could be updated to a real‐time model which would then be used to predict the motion of the target, to modify the IMRT leaf sequence on‐line to account for the target motion, and to calculate the delivery dose of the IMRT plan with consideration of the interplay effect. A lung case was chosen to demonstrate predictive tracking. The quality of the predictive tracking plan was compared with two commonly used 4D IMRT treatment planning techniques: maximum intensity projection (MIP) and planning on individual phases (IP). Results: For a realistic breathing motion, predictive tracking offered better plan quality than MIP and IP. PTV V97 was 90.4% for a MIP plan, 88.6% for an IP plan and 94.1% for a predictive tracking plan. Lung V20 was 20.1% for the MIP plan, 17.8% for the IP plan and 17.5% for the predictive tracking plan. Conclusion: Predictive tracking based on dynamic virtual patient modeling is a novel 4D planning/delivery technique which is capable of managing the real time 3D deformable motion of target without increasing the workload of treatment planning or time of delivery. For a realistic breathing motion with consideration of the interplay effect in beam delivery, predictive tracking gave better plan quality than IP and MIP.

Conflict of interest: Research supported by grant R01 LM009362.
TU‐G‐BRC‐03: A Novel Markerless Technique for Real‐Time Lung Tumor Tracking
Authors: Mao W , Solberg T
Published: November 2011

Purpose: A critical component missing in the radiotherapy process for lung cancer is real‐time monitoring of lung tumors. The large planning margin that is typically required to account for rumor motion compromises sparing of critical structures and normal tissues. A novel markerless method has been developed to monitor lung tumor motion during treatment.Methods: The method automatically identifies lung tumors directly on continuous MV treatment beam images. Prior information from planning CT and contours is used to generate three sets of DRRs for lung tumors, other moving organs, and static organs, respectively. Composite DRRs are produced by combining three sets of DRRs, with weighting factors assigned to compensate for different attenuation coefficients between MV and kV x‐ray energies. Individual locations of three set of DRR are optimized by comparing with acquired MV treatment beam images using a normalized cross correlation algorithm. The method was evaluated by monitoring a target moving inside a chest cavity phantom. It was also applied retrospectively to online MV images from lung cancer patients. Results: In phantom studies, the target and target motion characteristics were successfully located within seven different treatment fields; the detected target locations have a maximum deviation of 0.8 mm from expected locations. Lung tumors in lung patients were successfully tracked. Although the planning 4D CT indicated that the lung tumor motion range was within 0 mm, real‐time tracking suggested that: a) the lung tumor motion pattern is not regular; and b) the average tumor locations, the respiratory frequencies, and the tumor motion amplitude (range) vary considerably during treatment. Conclusions: This tracking method, which requires no implanted markers and can be performed with no additional imaging dose, will enable clinicians to reduce margins and safely deliver higher doses by accounting for the effects of displacement and motion during treatment.
TU‐G‐BRC‐07: Multileaf Collimator Tracking of Respiratory Motion Using a Novel X‐Ray Monitoring System
Authors: Krauss A , Fast M , Nill S , Oelfke U
Published: November 2011

Purpose: To demonstrate for the first time MLC tracking of respiratory motion based solely on x‐ray motion monitoring in the unique in‐line geometry. Methods: A Siemens Artiste linac was equipped with two flat‐panel imagers (FPI), one directly underneath the linac head, the other underneath the patient couch. The kV x‐ray beam pointed towards the linac head and was tilted by 5.4deg from the MV treatment beam axis, such that the two beams were spatially separated on both FPIs. A programmable phantom with an embedded metal marker reproduced a 3D lung tumor motion trace. The marker position was automatically detected in the kV images, which were acquired on the upper FPI at a frame‐rate of 7.1Hz. The marker coordinates were sent to our tumor tracking system, which adapted the aperture of a Siemens 160 MLC in real‐time. System latency was compensated through a linear regression predictor, which was trained on a 40s breathing data window. The lower FPI was used to assess both the system latency and the geometric tracking accuracy by identifying MV field and marker position. System latency was determined by tracking a sinusoidal motion trace without prediction and calculating the phase difference from least squares fits to the phantom and treatment field trajectories. Radiochromic films were used to assess dosimetric tracking accuracy. A static radiation delivery to the non‐moving target served as reference for the delivery to the moving phantom with and without tracking. Results: The total system latency was 740ms. Respiratory motion tracking yielded root mean squared deviations between phantom and MV field positions of 1.71mm (1.26mm) parallel (perpendicular) to the leaf travel direction. 2%/2mm gamma failure rates were decreased from 42% to 20%. Conclusions: We achieved accurate MLC tracking of irregular breathing motion (perpendicular to the treatment beam) based solely on x‐ray imagery.

Supported by Siemens Healthcare/CR.
TU‐G‐110‐01: Feasibility Study of Using Multi‐Pixel Photon Counter (MPPC) as Energy Resolved Photon Counting Detector
Authors: Xu Xiaocaho , Kim Joshua , Li Jia , Zhang T
Published: November 2011

Purpose: Energy resolved x‐ray photon counting detector is an enable technique for energy resolved CT system. A popular choice is Cd‐Te or CZT direct conversion x‐ray detector. But this kind of detector suffers low counting rate and therefore is unsuitable in clinical imaging. Multi‐Pixel Photon Counter (MPPC) is a new device that potentially can achieve much higher photon counting rate. In this study, we investigated the feasibility of using MPPC as x‐ray photon counting detector. Method and Materials: We designed and assembled a MPPC photon counting module with a Hamamatsu MPPC coupled with a LYSO scintillator. The photon pulses were recorded by a GHz digital oscilloscope and stored in a computer. We developed a signal pulse model which can be used to determine the instance and height of each pulse. To further increase the counting rate, a signal processing algorithm was used to discern multiple partially overlapped pulses. Results: Based on the position and height of the MPPC pulses, the time and energy of an x‐ray photon event can obtain by fitting the model with measured signal. The developed signal processing algorithm can further differentiate x‐ray photons that are piled up together. A higher than 20 Mcounts/s can easily achieve by MPPC counters. Conclusion: MPPC photon counter coupled with LYSO scintillator can achieve a much faster photon counting rate than Cd‐Te or CZT detector. It is a promising x‐ray photon counter that potentially can reduce energy resolved CT scanning time to a clinically acceptable range.
TU‐G‐110‐08: Feasibility of Tissue Composition Measurement with Dual Energy Computed Tomography
Authors: Ducote J L , Ding H , Molloi S
Published: November 2011

Purpose: To investigate the feasibility of tissue composition measurement with dual energy computed tomography as compositional information may help to better characterize suspicious lesions. Method and Materials: Simulations and experimental studies were performed for a flat panel dual energy dual kVp CT system. Simulations were performed to identify optimal beam energy combinations. A figure of merit (FOM) was used to determine the optimal dual energy signal to noise ratio with respect to mean glandular dose. Beam energies ranging from 40 to 140 kVp were simulated in 1 kVp increments. The distribution of dose between low and high energy images was simulated at intervals of 10%. An experimental calibration phantom of 3.175 cm in diameter was constructed from a polyoxymethylene plastic with cylindrical holes filled with water and oil. Similar size samples of pure adipose and lean bovine tissues were also prepared. The phantom and tissue samples were imaged with the dual energy CT system. The calibration phantom was used to estimate the water, lipid and protein contents of each tissue sample. Tissue composition results computed from images were compared to data from chemical analysis of prior tissue samples. Results: The predicted spectra from simulation which optimized the FOM were at beam energies of 40 kVp and 140 kVp with the mean glandular dose divided equally between each exposure. Given tube loading and system constraints, experimental beam energies for the dual kVp CT system were selected to be 50 kVp and 120 kVp. The percentage RMS errors of water, lipid and protein contents as compared to data from chemical analysis were 10.9% for the dual kVp technique. Conclusion: The results of this study suggest that the water, lipid, and protein content may be measured with dual energy CT with relatively good agreement. This might potentially be useful for characterizing suspicious lesions.
TU‐G‐110‐09: Spectral CT (SCT) Reconstruction Using Tight Wavelet Frames
Authors: Dong B , Jia X , Gu X , Jiang S
Published: November 2011

Purpose: X‐ray CT has been widely applied in a number of clinical and preclinical applications. However, the images are often insufficient to distinguish diagnostically crucial shading differences due to poor tissue contrast and inherent quantum noise. Recently, Spectral CT (SCT) base on photon counting technology has attracted a lot of attention due to its ability of providing full energy resolved tomography images. Currently, SCT is often reconstructed by using the conventional filtered backprojection (FBP) algorithms on each energy channel independently. Yet, it is expected that the anatomical features between energy channels are highly correlated. In this work, we propose an correlated iterative SCT reconstruction algorithm using tight wavelet frame based regularizations. Methods: In our study, we propose a model that reconstructs SCT images via solving an optimization problem. The objective function contains both a data fidelity term, requiring the consistency between reconstructed data and the measurement in each energy channel, and a regularization term applied along both the spatial dimension and the energy dimension. Bregman iteration method is used to solve the optimization model efficiently. To validate our algorithm, we synthesis a set of energy resolved x‐ray projections in fan‐beam scanning geometry on an NCAT digital phantom. Reconstruction results from our algorithm are compared with those from the conventional FBP algorithm. Results: It is found that our algorithm has lead to visually better image quality than the FBP algorithm. Signal‐to‐Noise Ratio (SNR) is used to evaluate the reconstruction quality. Our algorithm can enhance the SNR by a factor of 4–5 compared with the FBP algorithm. Conclusions: We have designed a wavelet frame based regularization method for SCT image reconstruction. Higher quality SCT images than that from FBP algorithms have been achieved.