bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐193: Evaluation of Three IMRT QA Techniques to Detect MLC Positioning Errors
Authors: Bergan A , Elson H , Lamba M , McGill B
Published: August 2010

Purpose: This study evaluates the effectiveness of three IMRT quality assurance (QA) techniques in detecting errors in the positioning of multileaf collimator (MLC) leaves. Method and Materials: Systematic errors were introduced into patient specific IMRT plans; errors of ±1 mm, ±2 mm, and ±3 mm were introduced to one bank of the MLC leaves. Each plan was measured using a diode array for each the following QA techniques: single fields with beams normal to the detector; composite of all beams normal to the detector; and a simulated treatment using all gantry and table angles. The measured data was compared to the appropriate unaltered plan using distance‐to‐agreement (DTA) and γ index analysis with 3%/3mm criteria. Results: The mean passing rates for single field measurements were: 0mm error 94.8±2.5, +3mm error 84.5±5.5, and −3mm error 84.6±7.4. Composite measurements had a mean passing rate of: 0mm error 97.8±1.5, +3mm error 78.2±10.6, and −3mm error 82.0±12.3. Simulated treatment results have a mean of: 0mm error 95.1±2.9, +3mm error 74.0±14.6, and −3mm error 76.2±12.6. The mean deviations in passing rate from the unaltered measurements were: single field measurement for +3mm −0.11±0.05 and − 3mm −0.11±0.07; composite measurement for +3mm −0.20±0.10 and −3mm − 0.16±0.12; simulated treatment deviation for +3mm −0.22±0.15 and −3mm − 0.20±0.11. Using ANOVA analysis demonstrates that the three plans are statistically identical in error detection for +1mm, +3mm, −2mm, and −3mm errors. Plans with +2mm and −1mm errors were statistically different but it was inconsistent which technique was more effective. Conclusion: The altered and unaltered plan QA measurements had a wide distribution of passing rates indicating a high degree of variability from plan‐to‐plan. There was no technique that indicated a greater sensitivity to introduced errors.
SU‐GG‐T‐207: Investigation of the Segmental‐ and Dynamic‐IMRT Delivery Performance for Combination of Varian 21iX‐S and CMS XiO Treatment Planning System
Authors: Kojima T , Tohyama N , Kodama T , Kawachi T , Iwase T , Shimizu T , Uno J , Hatano K , Kurooka M , Saitoh H
Published: August 2010

Purpose: The purpose of this investigation is to compare quality of plan, treatment time, monitor units (MUs) and dose delivery capability between dynamic and segmental IMRT for combination of Varian 21iX‐S and CMS XiO. Method and Materials: Head and neck (HN) and prostate IMRT were planned in both dynamic and segmental fashion using same dose objectives in the optimization process. Quality of plans was evaluated with isodose curves and dose‐volume‐histograms. Treatment time defined as time from the first beam‐on to the last beam‐off and MUs were compared. Dose rate of segmental and dynamic were 500 and 300 MU/min, respectively. Dosimetric verification was performed with 0.6 cc ionization chamber for point dose measurement and radiographic film for dose distribution. Results: In HN cases, dose conformity for PTV were slightly superior, however doses to parallel organs (e.g. parotid gland) were higher in dynamic delivery. MUs with dynamic delivery were lager by 20% for HN and prostate cases. Therefore, larger MUs lead more transmitted dose from MLC to parallel organs. Some reports mentioned that with dynamic delivery using other than XiO, treatment time could be shortened by half. But our results showed only 20% reduction for HN and comparable for prostate. The MLC sequence file of dynamic delivery was fairly large (320 control points/port), on the other hand, that of segmental was 1/6 of dynamic. Therefore, beam was kept off while treatment console read MLC sequence file (approximately 20 s/port for dynamic and 5 s/port for segmental, respectively). For HN cases, dose delivery capability was better in both point dose and dose distribution for segmental delivery. Due to higher MUs, dynamic delivery needs precise modeling especially for MLC transmission is required. Conclusion: Delivery performances are superior in segmental delivery, except for treatment time. To conclude, segmental delivery could be suitable for IMRT.
SU‐GG‐T‐214: Application of a Simple Transmission Dosimetry for Prevention of Loss of MLC Accident (LOMA) during Record and Verification (R&V) System Upgrade
Authors: Kim S , Oh S , Serago C , Gale A , Suh T
Published: August 2010

Purpose: To evaluate the feasibility of a simple cumulative‐fluence‐measurement‐based QA method for the prevention of loss of MLC accident (LOMA) during record and verification (R&V) system upgrade. We define LOMA as an accident IMRT delivery is made with MLC parameters lost. We introduce a simple transmission dosimetry method and its use for LOMA prevention QA. Methods and Materials: The procedures are; 1) get a baseline cumulative‐fluence pattern during regular treatments by therapists before upgrade, and 2) following the upgrade, repeat the same measurement by physicist(s) in QA mode. For the fluence measurement, a film holder was fabricated in a way that it; 1) doesn't interfere with accessory code and can stay in the wedge slot as needed, 2) causes no significant beam perturbation, 3) causes no clearance loss, and 4) can hold a radiochromic film centered. Stress level and execution time were evaluated. Optical density at a point was read and compared. Attenuation and surface dose were measured. Results: Among six therapists, four expressed “zero” stress and two did “1” in zero to 10 scale with 10 the highest. It needed less than 2 minutes including documentation but additional time to regular treatment was less than 30 seconds because documentation was done in spare time. For physicists, it took about 10 to 20 minutes per patient depending on the number of fields. Attenuation was less than 0.4% and surface dose increases were 0.0, 0.1, and 0.6% (w.r.t dmax dose) for 5×5, 10×10, and 20×20 field, respectively. Conclusions: The proposed method provided the confidence of data integrity in IMRT delivery during R&V system upgrade. It is simple to implement and will add either “no stress” or “minimal stress” to therapists. No significant time addition is expected for patient treatment. This method can be easily expanded for routine QA for LOMA prevention.
SU‐GG‐T‐397: Voxel Size Effect on Dose Mass Histograms of Head and Neck‐ IMRT Monte Carlo Treatments
Authors: Mora G , Li J , Fan J , Ma C
Published: August 2010

Purpose: Previous studies [1] demonstrated that Dose Volume Histogram (DMH) is a better parameter than DVH for evaluating treatment plans calculated by Monte Carlo (MC) simulations that may have large statistical uncertainties in low‐density regions such as air cavities and lung tissues. On other hand, it has been showed [2] that the voxel size may affect the dose distributions calculated by MC for head and neck region. In the present work we asses the voxel size effect on DMH for head and neck MC treatments. Method and Materials: Four IMRT head and neck cases were included in this study. MC patient simulation phantoms of different voxel sizes (2–9mm), were built from the same patient CT data. The EGS4 based MCSIM code and photon source models for 6 MV beams were used to calculate the isodose distributions, DVH and DMHs for both, PTV and critical structures. Results: Our results show significant differences between the DMHs calculated in the simulation phantoms of different voxel sizes (2–9mm). The effect is more significant for critical structures (up to 10%). DMH is more sensitive than DVH to the voxel size effect, however the accurate calculation of the DMH requires significantly less CPU time than the calculation of DVH. Conclusion: Our results suggest that 2 mm voxels should be used for the calculation of DMHs for head and neck for accurate treatment evaluation. Since the voxel size effect reduces the abiltiy of DMH to properly validate the plan, it may have a negative impact on the treatment outcome.
SU‐GG‐T‐399: Dosimetric Comparison of Monte Carlo and Ray Tracing of Cyberknife T Spine Treatment Plans
Authors: Lo A
Published: August 2010

Purpose: Cyberknife treatment involves many beams passing through lung before reaching the T spine target therefore tissue heterogeneity correction will have major effect on dose distribution. This study compares dose to the target and to critical structure for T Spine treatment plans generated from Multiplan with Monte Carlo and ray tracing for tissue heterogeneity correction. Method and Materials: Clinical T spine treatment plans based on ray tracing algorithm for tissue density correction were recalculated with Monte Carlo at high resolution with 2% uncertainty. Results including target dose, Conformity Index, target coverage and cord dose based on the two calculation methods are compared. Results: Based on clinical cases, the ratio of Monte Carlo results to ray tracing results are: target minimum dose 94% +/− 6%, target mean dose 97% +/− 2%, target maximum dose 101% +/− 3%, Conformity Index 93% +/− 3%, coverage 95% +/− 2% and cord maximum dose 96% +/− 3%. Monte Carlo plans tend to have more dose heterogeneity with lower target minimum dose, lower target mean dose and similar target maximum dose. Coverage and Conformity Index are lower for Monte Carlo by 5% to 7% because the optimized ray tracing plans are no longer optimal when recalculated with Monte Carlo. Conclusion: Ray tracing treatment plan tends to under dose the T spine target and cord by 3% to 4%. At the lung/bone interface, the isodose line tends to pull toward the vertebral body and the target voxels closest to the lung will have the biggest dose drop therefore the lower target minimum dose. It is recommended to start Multiplan optimization with Monte Carlo for T spine treatment plan in order to get realistic dose to target and cord.
SU‐GG‐T‐403: A Coarse Mesh Transport Method for the Calculation of Photon Energy Deposition in Tissue
Authors: Hayward R , Rahnema F , Zhang D
Published: August 2010

Purpose: To develop and test a novel, transport‐based method for calculating the energy deposition of a photon beam in tissue. Method and Materials: The new method is based on a hybrid Monte Carlo‐Deterministic Coarse Mesh Transport Method COMET. COMET is a method for solving the linear Boltzmann Transport Equation based on an incident angular current expansion. It has been shown to perform well for 2D coupled photon‐electron transport calculations aimed at determining the energy deposition of a photon beam. The COMET method uses pre‐computed Monte Carlo‐based response expansion coefficients to achieve accuracy comparable to Monte Carlo methods in a fraction of the time. The current work extends the photon transport capability of the COMET method to handle 3D geometry and to simulate realistic photon sources. The method is tested with a simple benchmark problem consisting of a 20×20×20cm water phantom irradiated by a collimated, polyenergetic photon source at a source‐to‐surface distance (SSD) of 80cm. Although the COMET mesh size is arbitrary, the phantom is divided into 1×1×1cm voxels for convenience. The accuracy of the method is evaluated by comparison to a reference calculation performed with EGSnrc. Results: The distribution of energy deposition was examined voxel by voxel. The largest error for any voxel is found to be less than 3.3% of the maximum energy deposition value from the reference solution. The relative standard error for each voxel in the reference solution is less than 0.5%. The COMET solution took 0.27 core‐hours to compute compared with 84 core‐hours for the reference solution. Conclusion: The work indicates that the COMET method holds promise for fast and accurate 3D photon and electron dose calculations. Furthermore, sources of error are identified and suggestions are made to improve the accuracy of the new method during future development.
SU‐GG‐T‐412: PyEGS5 ‐ a Python Programming Interface for EGS5
Authors: Ma Y , Xing L
Published: August 2010

INTRODUCTION: EGS5 is the state‐of‐the‐art implementation of the Electron Gamma Shower (EGS) Monte Carlo code system, which is written purely in Fortran language. The Fortran language is an efficient computer language for numerical calculation, however, it is much limited in functionalities like GUI, plotting. In order to make EGS5 an easy‐to‐use tool, a Python programming interface to EGS5 and a pythonic Monte Carlo simulation environment for radiation transport calculations has been developed, referred to as PyEGS5. METHOD AND MATERIALS: With binding to Python, PyEGS5 can be used in a scripting and interpreted way, while maintaining the efficiency of the Fortran binary code. As a powerful modern programming language, Python brings to EGS5 many advanced programming features and resources, with which users can create full‐featured Monte Carlo simulation applications with much less efforts than using Fortran language. RESULT: PyEGS5 is a very useful tool in medical physics research, fast‐prototyping of medical physics devices and teaching Monte Carlo simulation to medical physics students. PyEGS5 will be provided as an open source code to anybody who requires it, under the general GNU license (GNL). CONCLUSION: PyEGS5 provides the medical physics community with an easy‐to‐use programming interface to EGS5 code system which combines the advantages of the Python language and the Fortran language.
SU‐GG‐T‐417: Evaluation of a Commercial Monte Carlo Dose Calculation Algorithm for Electron Beam Treatment Planning
Authors: chamberland E , Lachance B , Beaulieu L
Published: August 2010

Purpose: To evaluate the accuracy of the electron Monte Carlo (eMC) dose calculation algorithm included in the Eclipse treatment planning system. Method and Materials: Multiple tests were planned to explore the system behaviour in configurations encountered in clinical practices. The first series of test were performed in a homogeneous water phantom. Measured and eMC calculated dose distributions were compared for different combinations of energy/applicator/depth. Three different inhomogeneous solid phantoms simulating high and low density materials were constructed to explore various heterogeneity conditions; a small air cylinder, a lung phantom and a chest wall phantom. The test under study is the lung inhomogeneity which consists of cork slabs. In all cases, comparisons are made between measurements, carried out by means of XV‐2 films, and eMC and Pinnacle computations. Finally, the evaluation of the eMC algorithm for a clinical case, a nose cancer, was conducted. Results: The eMC validation in the water phantom and in the lung phantom is shown to be accurate. The maximum observed discrepancy between measurements and eMC is 2.5%. For the lung case, Pinnacle does not correctly model the electron scattering. The retrospective study of the clinical case, which presents scatter perturbations by air cavities, shows planar dose difference up to 20% between Pinnacle and eMC. Conclusion: eMC algorithm showed good agreements with measurements in simple homogeneous and heterogeneous phantoms. Comparatively to the electron pencil beam algorithms of Pinnacle, the eMC calculations more precisely predict large dose perturbations due to inhomonegenities.
SU‐GG‐T‐428: Photon Beam Spectrum Characterization Using Scatter Radiation Analysis
Authors: Hawwari M , Lamba M , Elson H , Spitz H , Miron A , Glover S
Published: August 2010

Purpose: A method is described to characterize a linac bremsstrahlung spectrum. The method employs a combination of monoenergetic scatter simulations, polyenergetic scatter measurements, and matrix solutions. Method and Materials: Monte Carlo simulations were used to predict the ratio of primary to scattered photons for narrow mono‐energetic photon beams at 9 different locations, with 10 degree increments and 15 cm from a scattering material. Measurements were performed in the same geometry using the photon beams produced by linear accelerators. A linear matrix system, A×F=T, was developed to describe the scattering interactions and their relationship to the primary spectrum. Matrix “A” is the monoenergetic scatter kernel determined from the Monte Carlo simulations, “F” is the incident photon spectrum, and “T” represents the scatter distribution characterized by empirical measurement. Direct matrix inversion methods produce results that are not physically consistent due to errors inherent in the system. Tikhonov regularization methods were applied to address the effects of these errors and solve the system for physically consistent bremsstrahlung spectra. The technique was applied to two photon energy spectra ‐a helical tomotherapy accelerator operating at therapeutic energy and at imaging energy. Results: The resulting spectra were qualitatively and quantitatively similar to other published data and consistent with expected behavior such as maximum photon energy. Conclusion: The results of this research provide a method to empirically characterize the primary radiation energy spectrum produced by a linear accelerator. Key words: photon energy, spectrum, scatter analysis, regularization, Tikhonov
SU‐GG‐T‐429: Implementation of a Geant4 Based GPU Monte Carlo Algorithm and Benchmarking of an IMRT Patient Plan
Authors: Jahnke L , Fleckenstein J , Hesser J , Wenz F
Published: August 2010

Purpose: To calculate the Monte Carlo based dose distribution of an IMRT prostate case on the GPU and thereby significantly increase the computation speed. Method and Materials: A Geant4 based head simulation of an Elekta Synergy accelerator head was utilized to calculate a phase space plane between the head and the patient geometry. An NVIDIA CUDA implementation of the GEANT4 low energy transportation algorithm was programmed validated for regular field shapes and then used to calculate the IMRT dose distribution of one prostate patient. The dose distribution was also calculated using GEANT4 on the same patient geometry. In the GPU implementation as well as in GEANT4 no variance reduction techniques were used. The IMRT patient was optimized with the Corvus treatment planning system (NOMOS). Results: The results showed a good agreement (gamma criteria 4%/3mm > 97 %) between Geant4 CPU based simulations and the GPU based simulations. The computation time was approximately the same (12 minutes) for a 256 node cluster and 2 NVIDIA GTX 295 GPUs installed on one Intel quad core computer. This compares very well to time modern Voxel Monte Carlo based treatment planning systems need for one recalculation. Conclusion: This implementation proves the possibility to calculate complex IMRT plan simulations with a Monte Carlo dose engine on GPUs. This work is the starting point for future investigations leading to new variance reduction techniques suitable for GPUs and improving the speed of Monte Carlo simulations on standard workstations.
SU‐GG‐T‐432: Implementation of Modular Phase Space IO in Geant4 with Enhanced Latch Capability
Authors: Sawkey D , Faddegon B , Paganetti H , Perl J
Published: August 2010

Purpose: Write general‐purpose, modular code for phase space input and output in Geant4 including latch and npass. Method and Materials: Geant4.9.3 does not include the ability to read or write phase space files. These files are useful for dividing the simulation into parts, for example, into patient‐independent and patient‐specific parts. Stand‐alone classes inheriting from G4VPrimitiveScorer and G4VPrimaryGenerator were written for writing and reading phase space in IAEA format. Latch mechanisms are not stand‐alone and require implementation of (provided) G4User classes for tracking. Results: Phase space I/O is implemented in Geant4. For writing, several types of surfaces are allowed, including planes, spherical sections, cylindrical sections, surfaces enclosing a volume. Multiple surfaces of any orientation and geometry are allowed. The concept of latch in BEAMnrc (particle interacted in a region) was expanded to include: particle interacted in a region; particle passed through a region; similarly for ancestors; type of interaction in particle's history; type of ancestor particle; and user‐defined. The user defines the interactions, particles, and regions of interest via get/set functions. As in BEAMnrc, an integer npass records the number of times a particle crosses a phase space surface, which is particularly valuable in studies of backscatter. The MGH proton treatment facility was simulated with phase space files recorded at the phantom surface. Spectra using the various latch cuts were generated, demonstrating the capabilities of latching on regions, interactions, or ancestors. Conclusions: Phase space I/O capabilities have been implemented for Geant4. The classes are easy to incorporate into existing code, allowing writing on different surface geometries, and extend the Latch functionality of BEAMnrc. Support: Support from NIH grant 1R01CA140735‐01.
SU‐GG‐T‐437: The Depth‐Dose Curves of 126 MeV Antiprotons in Water Using MCNPX Simulation Code
Authors: Handley S , Ahmad S
Published: August 2010

Purpose: To simulate dose contributions from various annihilation products to the depth dose profile for the irradiation of 126 MeV antiprotons in water using the MCNPX simulation code. Methods and Materials: A cylindrical water phantom (100 cm long, 15 cm radius) was generated using MCNPX version 27‐b. Cylindrical detectors (0.5 mm depth, 1 cm radius) of water were positioned along the central axis of the beam. Antiprotons with 126 MeV and 5 cm × 5 cm field size were used. Particle and photon transport in the code included pions, kaons, muons, secondary protons, neutrons, gamma and other heavy and light ions. Tallies utilized within the cylindrical detector region included the “+F6” collision heating tally and individualized “F6” tallies for detailing the energy depositions for the particles averaged over detector elements. A total of 100,000 histories were run. The depth‐dose profile from antiprotons was compared to that of protons of identical energy and field size. The relative contributions from various annihilation products to the total antiproton depth‐dose were studied. Results: In shallow depth region, the dose levels for antiproton were slightly higher compared to proton due to antiproton's annihilations in flight. In Bragg peak region, the dose levels with antiproton were augmented by higher than 2 compared with proton, at iso‐fluence, mainly due to antiproton's annihilations at rest. At peak depth, the contributions from antiprotons (without annihilations) were about two and six times higher than that from secondary protons and annihilation pions, respectively. The remaining part of the total dose was attributed to contributions from muons, kaons, gamma, light and heavy ions. Conclusions: Our results are in excellent agreement with recent FLUKA simulation results. However, somewhat higher contributions from kaons to the total dose at the Bragg peak were observed compared to the previous study.
SU‐GG‐T‐438: Dose to Medium or Dose to a Water Cavity Embedded in Medium? A Monte Carlo Study
Authors: Enger S , Ahnesjo A , Beaulieu L
Published: August 2010

Purpose: The target for radiotherapy is to sterilize cells by imposing damage to their DNA content. It is therefore of interest to study the relations between the dose calculated to a tissue medium, Dm,m, with an representative average atomic composition versus the dose Dn,m specifically absorbed by the cell nuclei, and the dose Dw,m to a cell nuclei surrogate represented as a water cavity embedded into tissue. The simulations were performed for six types of tissues and three different brachytherapy sources. Methods and Materials: Absorbed dose calculations were performed by GEANT4 MC code version 9.2 using the Penelope physics package. Three different sources, 192Ir to represent high energy conditions, 169Yb for intermediate energies and a low energy brachytherapy source 125I, were simulated. The photon spectra used in this study were taken from http://www.physics.carleton.ca/clrp/seed_database. The 192Ir spectra was from Nucletron, microSelectron‐HDR v2 and for 125I from Nucletron, SelectSeed, 130.002. Particle spectra for 192Ir and energy spectra for 192I were also scored to calculate the dose with different cavity theories and compare it with MC calculated doses. Results: The MC calculated Dm,m, Dw,m and Dn,m ratio shows the largest value for 125I brachytherapy source and the cortical bone material, adipose tissue and prostate tissues(ICRU). The difference between Dw,m and Dn,m is also largest for the cortical bone and 125I source. For the 192Ir source, the ratio was 1 for the soft tissues while for the cortical bone it was higher. Conclusion: Monte Carlo calculations made it possible to report the dose as absorbed dose to medium. Accurate reporting of treatment planning requires a stringent standard for dose definition. MC calculations can be used to develop conversion factors to convert dose according to different definitions for different brachytherapy sources.
SU‐GG‐T‐440: Graphical User Interface for Monte Carlo Phase Space Field Trimming
Authors: Sivayogan T , Chow J
Published: August 2010

Purpose: A graphical user interface (GUI) was developed to trim a radiation field of a phase space file to the dimensions of an arbitrary field as needed. This GUI is expected to be used in the monitor unit calculations on electron and orthovoltage x‐ray therapy under certain assumptions. Methods and Materials: The GUI and the phase space trimming algorithm were developed using MATLAB with compiled C code for fast read and write operations. The input phase space files were generated using EGSnrc‐based BEAMnrc through Monte Carlo simulations of the Varian 21 EX LINAC at SSD = 100 cm for electron beam energies of 4, 6, 9, 12, and 16 MeV and a 10 × 10 cm2 applicator. Various fields were tested including circles, triangles, and 2 irregular shapes. The user interacts with the GUI to provide the specifications for the trimming operation, which include scaling and orienting the arbitrary field within the scoring plane of the phase space file. Results: Verification of the trimming process was performed by comparing the plots of the trimmed particle distributions with the arbitrary field. The GUI took under a minute to trim a 0.5 gigabyte file with 15 million particle histories using a 4 × 8 cm2 irregular ‘E’‐shaped field. Reading and writing particle histories was the most time consuming process, whereas the trimming operation was the least. Conclusions: The phase space trimming GUI is a platform independent tool that can trim any arbitrary field as needed from a bigger phase space file.
SU‐GG‐T‐441: Monte Carlo Dosi metric Verification Based on Double Source Model
Authors: Li G , Zheng H , Wu Y
Published: August 2010

Purpose: In dose calculation and dosimetric verification for radiotherapy, the Monte Carlo method is a “gold rule”in accuracy given the same condition. Yet the results of the traditional Monte Carlo's method may disagree with the practical situation due to lack of practical information of a given medical accelerator such as energy spectra. For another, the previous dosimetric verification method mainly focused on 1D or 2D verification by use of film, thermoluminescence detector, ionization chamber, etc, and they usually fail to apply in vivo but vitro of a patient. Considering whatever producing high energy photon or electron beam, the medical accelerator also produced contamination radiation beam, such as photon beam to electron contamination. With these, the purpose of this study was to improve the accuracy of the dosimetric verification in Monte Carlo method. Method and Materials: A double source model combined the Monte Carlo method for the photon and electron radiation was constructed. Namely, the photon and electron energy spectra, photon or electron contamination etc were input into the Monte Carlo engine as EGSnrc to realize the double source dose calculation, and the superimposed results between electron dose map and photon dose map were as the final one. Results: The testing samples from AAPM report No.55 (energy as 4MeV and 18MeV) indicated that the root‐mean‐square error was less than 0.21% in the 4MeV' sample and 0.18% in the 18MeV's sample respectively, comparing with the measurement data of corresboding centeral axis percentage depth dose in this report. Conclusion: This method may not only overcome the traditional dosimetric verification confine in 1D/2D dose map, but also get the 3D dose map of the whole space and increase the accuracy of the dosimetric verification. So it can be applied to the clinic dosimetric verification and quality assurance in radiotherapy.
MO‐A‐204C‐02: Breast MRI Quality Control
Authors: Reeve D
Published: August 2010

Quality control of MRI systems used for diagnostic breast MR imaging and biopsy guidance is important to ensure the production of high quality images. Breast MR images may be acquired using dedicated breast MRI scanners, whole body MRI scanners with detachable tabletop breast coils or tables designed with integrated breast coils. 1.5T and 3T multi‐channel arrays are now available. Many of these coils are designed to enable MR‐guided breast biopsy.

In May 2010 the ACR launched the ACR Breast Magnetic Resonance Imaging Accreditation Program. The program requires that a medical physicist/MR scientist perform MRI system testing after installation, annually and following major upgrade or repair. Testing must include annual evaluation of all breast imaging and biopsy coils used clinically.

Learning Objectives:

1. Describe different breast coil designs

2. Discuss breast coil quality control procedures

3. Provide an overview of the ACR Breast MRI Accreditation Program including quality control requirements
MO‐D‐204B‐08: Classification and Characterization of Tumor Subpopulations Using Molecular Imaging
Authors: Song C , Nyflot M , Harari P , Perlman S , Jeraj R
Published: August 2010

Purpose: Distinct subpopulations of tumor cells with varying characteristics exist within a single neoplasm. The aim of this study was to develop a classification scheme for tumor subpopulations and investigate their characteristics and spatial distributions. Method and Materials: Eight HNSCC patients underwent PET/CT scans with [18F]FDG (a surrogate of metabolism), [18F]FLT (cell proliferation), and [61Cu]CuATSM (hypoxia). CT images were co‐registered and transformation matrices were applied to corresponding PET images. Five different clustering algorithms were utilized to classify voxels within a tumor ROI. By using the Silhouette validity index, performance of the clustering algorithms was evaluated and the optimal number of clusters was determined for each tumor. Mean SUVs were calculated for each subpopulation and then normalized to the mean SUV for an entire tumor. Results: The k‐means algorithm was used in this study since it gave the highest value of the Silhouette validity index. Seven tumors were partitioned: one into two subpopulations and six into three subpopulations. The number of clusters for the remaining tumor was much greater than those for the others, which might be caused by the misregistration between CT and PET. For the three partition cases, the subpopulations were found to be spatially separated into peripheral, central and intermediate regions. FDG uptake was 55% lower for the peripheral subpopulations and 19% lower for central subpopulations relative to the overall mean. On the other hand, FLT uptake was 51% lower for the peripheral subpopulations but 52% higher for the central subpopulations. However, no significant difference in CuATSM uptake among subpopulations was observed. Conclusion: We demonstrated that tumors can be partitioned into multiple subpopulations with distinct characteristics using multi‐phenotypic molecular imaging. This subpopulation‐based study may lead to better understanding in designing personalized cancer therapy.
MO‐D‐204C‐01: Imaging Tumor Vasculature and Angiogenesis: Biology, MR Imaging, and Anti‐Angiogenic Therapies
Authors: Metheny‐Barlow L , Brown S , Maity A
Published: August 2010

Tumor angiogenesis is the important biological process whereby new blood vessels are formed to supply nutrients and oxygen and to remove waste products for growing tumors. Angiogenesis plays key roles in forming and regulating the tumor micro‐environment, enabling metastatic disease, and greatly affects the delivery and response of targeted therapeutic agents. Targeting the tumor vasculature may represent a promising strategy to inhibit tumor growth and progression. Thus, this key biological process is being vigorously studied with the goal of impacting human clinical care. Physical approaches to understanding tumor angiogenesis include magnetic resonance imaging (MRI), which through various dynamic techniques can assess blood flow and other bioanatomic parameters relevant to angiogenesis. These advanced imaging techniques can be used in both pre‐clinical animal models as well as humans. Importantly, anti‐angiogenic therapies include pharmacologic and biologic agents that target tumor vascular through various biomolecular mechanisms, and tumor response can be monitored using advanced MR imaging.

For the benefit of the medical physicist who may be involved with angiogenesis research using MRI, targeted biochemical agents, and/or ionizing radiation, this symposium will review the biology of tumor angiogenesis, advanced MR imaging techniques, and translational efforts, including clinical trials and angiogenesis research challenges.

Specific objectives of the symposium are to:

1. Provide a primer on the biology of tumor angiogenesis and the tumor microenvironment

2. Review the important role of angiogenesis for the formation of metastases

3. Discuss biological mechanisms for the interruption of angiogenesis that would lead to a therapeutic result

4. Describe pre‐clinical and clinical magnetic resonance imaging techniques and applications for tumor vascular imaging

5. Review techniques and research challenges for quantitative MR imaging of angiogenesis, including national initiatives

6. Describe promising anti‐angiogenic therapies with targeted biochemical agents and ionizing radiation

7. Describe angiogenesis clinical trials, challenges in translating angiogenesis research to the clinic, and roles for medical physicists in angiogenesis imaging and therapeutics.
MO‐EE‐A3‐01: Feasibility Study on Four‐Dimensional Dose Reconstruction of Radiation Delivery
Authors: Jung J , Yeo I , Kim J , Yi B
Published: August 2010

Purpose: When an intensity modulated radiation beam is used to a moving target, the two time variables due to miss‐synchronization can cause unpredicted dose delivery. Exit dosimetry possesses information on delivered radiation to the target. Using a continuous scan (cine) mode of electronic portal imaging device (EPID), our goal is to use the temporal images related to the target motion and the beam, and perform dose reconstruction. Method: To evaluate this hypothesis, firstly, cine mode acquisition was compared with integration mode acquisition on EPID (IAS3 and As 1000). We have delivered open and clinical beams using 6MV at 300MU/min to EPID. Secondly, in‐phantom film and exit EPID dosimetry for the two modes was performed on a moving platform using a forwardly‐advancing beam that generates a pyramid dose shape. Beam delivery was gated for ten steps of 10% phase duration. Film was left for ten deliveries, but EPID images were acquired ten times on integration mode which effectively simulates cine acquisition. While a documented integration mode was used, the cine acquisition can be used clinically. In‐phantom dose was reconstructed from the EPID images of each phase and the reconstructed dose was summed and compared with the in‐phantom film dose. For dose reconstruction, we used our Monte Carlo response‐based algorithm documented previously. Results: The sum of the cine acquisition agreed with (1%) the integrated acquisition during step‐and‐shoot delivery. The discrepancy was variable with delivered MUs and number of segments due to beam instability at start of acquisition and reading loss for cine mode during MLC movement. For sliding‐window delivery, the cine agreed with the other (0.5%). The reconstructed dose agreed with the measurement within 1.4% at the isocenter. Further evaluation with more results will be presented. Conclusion: Feasibility of 4D dose reconstruction was demonstrated. In part supported by Varian Medical Systems.
MO‐EE‐A3‐03: Using Control Charts to Analyze the Patient Specific Nasopharyngeal Carcinoma IMRT QA
Authors: Sanghangthum T , Pawlicki T , Suriyapee S , Srisatit S
Published: August 2010

Purpose: Control charts are an effective statistical tool to control process variation by allowing the separation of systematic causes from random causes of error. In this work, we investigate the use of standard deviation (SD) charts and average (X‐bar) charts to identify systematic errors in patient‐specific IMRT QA. Method and Materials: Patient‐specific IMRT QA was done for 270 nasopharyngeal carcinoma plans using a MapCheck 2D diode array. All MLC‐based IMRT plans were generated using the Eclipse planning system for 6 MV on a Varian Clinac 21 or 23 EX linear accelerator. The plans of the patients during March 22, 2007 to February 10, 2010 were observed. Five points at center and 3 cm upper, lower, right, and left (except the high dose gradient point) from MapCheck were compared to those points from Eclipse. The dose differences between measurement and calculation were prospectively plotted each on X‐bar and SD control charts. The first fifty points were used to calculate the control limits. The comparison was also done after out‐of‐control points were removed and the limits were recalculated. Results: For the X‐bar control chart, the center‐line, upper and lower control limits are: −0.50%, 3.36%, and −4.36%, respectively. For the SD control charts, the center‐line, upper, and lower control limits were 2.70%, 5.65%, and 0%, respectively. The systematic errors could identify setup error, incomplete field exposure, and wrong energy for calibration factor, while SD chart could identify setup error and MLC interlock in some field. Conclusion: The SD chart is used for the purpose of identifying deviation in individual, while X‐bar chart is used for the population. The X‐bar chart gives more details of error than the SD chart. However, using both X‐bar and SD charts could provide more information about IMRT QA.
TU‐D‐BRA‐03: Real‐Time‐Image Guidance in Radiation Therapy: Is There a Role for Ultrasound Imaging?
Authors: Hristov D , Schlosser J , Salisbury K , Oralkan O , Khuri‐Yakub P
Published: August 2010

The curative potential of External Beam Radiation Therapy (EBRT) is critically dependent on having the ability to accurately aim radiation beams at intended targets while avoiding surrounding healthy tissues. Cone‐beam computed tomography, planar x‐ray imaging, radiographic or electromagnetic tracking of implanted fiducials, as well as operator‐performed ultrasound are currently used for EBRT image guidance. However, these technologies are incapable of addressing the challenge of real‐time volumetric (4D) visualization, localization, and tracking of soft‐tissue motion and deformation concurrent with treatment beam delivery. Thus a significant opportunity exists for improving the therapeutic ratio and the safety of EBRT. We will present and discuss two solutions that can realize this opportunity through the integration of spatially localized, remotely controlled operator‐free ultrasound imaging with radiation delivery systems.

The first approach relies on a custom designed compact ultrasound probe based on two‐dimensional matrix array of capacitive micro‐machined ultrasonic transducers integrated with radiofrequency electronics. For operator‐free imaging, the probe is to be fixed to a subject by a belt with appropriate acoustical coupling. Dedicated beam forming methodology and image reconstruction is necessary to enable large volume data collection at a volume rate of 3 Hz or higher.

The second approach employs a novel, minimally interfering, tele‐robotic ultrasound imaging based on commercial transducers. It uses a customized human‐safe robotic manipulator to control the pressure and pitch of an abdominal probe while avoiding gantry collisions. A haptic device is integrated to remotely control the robotic manipulator motion and image acquisition outside the therapy room.

Learning objectives:

1. Understand basic relationships between ultrasound imaging system design and performance parameters such as spatial resolution, frame rate, and field of view. Recognize the dependencies between these parameters.

2. Identify limitations of current EBRT ultrasound guidance systems and identify physics, design and workflow causes behind them.

3. Understand how remote‐operator free imaging and appropriately designed workflow can enable real‐time soft‐tissue image guidance concurrent with radiation delivery and reduce ultrasound localization uncertainties.

4. Recognize potential interferences between the radiation delivery system and the operator‐free imaging system and appreciate their magnitude and mutual impact.
TU‐D‐204B‐05: Cone‐Beam CT for Guidance of Spine Surgery: Performance and Integration of a New High‐Performance C‐Arm Prototype
Authors: Schafer S , Otake Y , Uneri A , Mirota D , Nithiananthan S , Zbijewski W , Stayman J , Schmidgunst C , Bulitta C , Khanna A , Siewerdsen J
Published: August 2010

Purpose: A prototype mobile C‐arm incorporating a flat‐panel detector (FPD) for high‐quality cone‐beam CT (CBCT) is under investigation for spine surgery. This work describes the image quality and dose in cervical, thoracic, and lumbar spine surgery and integration with novel navigation subsystems critical to high‐precision surgical guidance, including: tracking, video augmentation, deformable registration, and multi‐modality visualization. Method and Materials: Image quality, patient dose, and in‐room dose were assessed in phantom and cadaver studies approximating spine surgery. An open‐source software architecture was employed for integration of navigation systems based upon the CISST libraries linked to 3D Slicer. For spine surgery, a novel video‐based tracking and augmentation system was developed to facilitate high‐precision minimally invasive techniques. Target registration error (TRE) and accuracy of overlay were assessed. Deformable registration of preoperative and intraoperative images was based upon a fast implementation of the Demons algorithm. Results: Image quality demonstrated sub‐mm spatial resolution and soft‐tissue visibility; protocols were identified for “standard” and “high‐quality” imaging of the spine ‐ respectively for bone visualization (100 kVp, 2.4 mA, 200 projections, 1.6 mGy) and for soft‐tissue (100 kVp, 5.0 mA, 400 projections, 7.1 mGy). The TRE for video‐based and infrared tracking systems was 0.67 and 0.54 mm, respectively, and the accuracy of video overlay was 1.0 mm for the integrated video‐based tracker, compared to 1.3 mm for separate video and infrared trackers. Deformable registration demonstrated accuracy on the order of the voxel size on timescales consistent with surgical application. Conclusion: The first evaluation of an integrated mobile CBCT and guidance systems for spine surgery was demonstrated and characterized, emphasizing a flexible architecture of application‐specific navigation technologies. Drawing upon a decade of research in C‐arm CBCT, a new clinical prototype C‐arm is realized and undergoing evaluation and translation to spine surgery trials. Research supported by the NIH and Siemens Healthcare.
TU‐E‐204B‐03: A Multiregion Algorithm for Robust Lung Tumor Tracking with Portal Image Sequences
Authors: Rottmann J , Aristophanous M , Chen A , Court L , Berbeco R
Published: August 2010

Purpose: Methods for online lung tumor tracking during radio‐therapy are desirable for a variety of applications that have the potential to vastly improve treatment accuracy, dose conformity and sparing of healthy tissue. Using the MV beam and portal imager for this purpose is preferable as there is no additional imaging dose and the output is the location of the target in the beam's‐eye‐view. Method and Materials: We present a multiregion algorithm that utilizes the on‐board portal imager of the treatment machine to track lung tumors without implanted fiducial markers. Multiple regions with unique image structures are automatically identified and optimized based on an iterative procedure. Each region is tracked independently throughout the treatment, making the algorithm robust to target deformations, rotations and partial occlusions. To quantify the performance, the proposed algorithm was retrospectively applied to portal image sequences from a dynamic chest phantom study as well as an SBRT treatment performed at our institution. The results were compared to manual tracking by an expert. Results: For the phantom data the tracking error was found to be smaller than 1mm and for the patient data smaller than 2mm, which was in the same range as the uncertainty of the reference. All optimized regions were able to be tracked on all images in both phantom and clinical sequences. The algorithm allows tracking of 15 regions at 2fps, the rate at which the images are clinically acquired. Conclusion: We have developed and tested a robust algorithm to track lung tumors on portal image sequences without the use of fiducial markers or user intervention. The algorithm has the potential to be implemented in real time and is not dependent on prior information of the exact tumor motion range during treatment (unlike classification algorithms which generally require this). Conflict of Interest: Varian Medical Systems Inc.
TU‐E‐204B‐06: Real Time Tumor Tracking during VMAT Treatment
Authors: Zhuang L , Liang J , Yan D , Drake D , Tyagi N , Ionascu D
Published: August 2010

Purpose: Intra‐fraction variability of lung tumor position during radiotherapy treatment may cause large dose discrepancy especially for VMAT delivery. Purpose of this work is to reconstruct tumor 3D motion trajectory during VMAT delivery in real‐time based on concomitant CBCT projection images and detect motion irregularities to quantify them for further treatment decision. Method and Materials: A tool was designed to reconstruct lung tumor 3D trajectory during VMAT delivery in real‐time. Our method allows us to detect and quantify abrupt inter‐frame motion during treatment. Tumor 2D position in CBCT projection image is obtained from its registration to certain phase of 4DCT DRR. To assess the efficacy of our method, we developed a lung‐like phantom moving in pre‐determined motion patterns from regular to complex (a Lujan model and three real tumor trajectories). The complex tumor trajectory included an intentional abrupt change in position as well as baseline shifts, amplitude and period variations. Detected trajectory based on our method was compared with the tumor actual trajectory for two tumors, one regular in shape with good contrast (tumorl) and one irregular in shape with poor contrast to adjacent material (tumor2). Results: Experiments show good accuracy in phantom study. For tumorl, reconstructed mean position is (−0.36±0.4, −0.1±0.6, − 0.2±0.5) mm from actual mean position. For tumor2, reconstructed mean position is (−0.34±0.9, 0.0±0.2, −0.1±0.2) mm from actual mean position. When tumors move under abnormal patient breathing curve, the intentional position shift can be detected, which shows the potential of our tool in clinical usage. Conclusion: We successfully developed a tool that can be used to track tumor trajectory during VMAT delivery in real‐time. Our technique allows us to characterize tumor's motion during treatment and enables one to adjust or stop treatment when tumor motion is out of pre‐established tolerance range. Research sponsored by Elekta and Philips