bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐407: Full Monte Carlo Computation of K Correction Factors Calculated in Tomotherapy Static and Helical Deliveries for Future Ion Chamber Reference Dosimetry Protocols of Non Standard Beams
Authors: Sterpin E , Mackie T , Lu W , Olivera G , Vynckier S
Published: April 2010

Purpose: Calculate correction factors for ion chamber dosimetry using Monte Carlo (MC) simulations for future IAEA/AAPM protocols adapted to Tomotherapy treatments. Material and methods: The formalism in Alfonso et al (Med. Phys. 35 2008) introduced two corrections factors: defined for a “machine‐specific‐reference” field fMSR (10×5 cm2 field, source‐surface distance of 85 cm) and for a “plan‐class‐specific‐reference” field, fPCSR, closer to actual clinical treatments. Here, fPCSR was a helical sequence delivering a centered cylindrical homogeneous dose over 10 cm in a homogeneous cylindrical phantom. The k factors were calculated using MC with accurate simulation of static and helical deliveries (using TomoPen, based on PENELOPE) and detailed modeling of the geometry of the ion chambers Exradin A1SL, PTW‐30013, Wellhöfer IC‐70 and NE‐2571. Calculations in the phantoms were performed by the “cavity” EGS++ user code, for static beams, and PENELOPE for both helical and static beams. Correction factors were calculated from the formulas
urn:x-wiley:00942405:media:mp1889:mp1889-math-0003 and
urn:x-wiley:00942405:media:mp1889:mp1889-math-0004 where Dm is the dose at the reference point in medium m (water or Solid Water™) and a is the dose averaged over the air cavity. Results: For the A1SL chamber, equaled 0.997±0.001 (3σ), which is consistent with the values previously reported using existing protocols. was estimated at 0.995±0.002 for the procedure chosen. The work is in progress for the ion chambers listed above and other Tomotherapy “PCSR” settings, like a typical bilateral head and neck treatment delivery planned on a phantom. Conclusions: A powerful MC method is proposed here to compute accurate correction factors for Tomotherapy treatments. The data obtained may be of primary importance during the final definition of a new dosimetry protocol, adapted to nonstandard treatments like Tomotherapy and may also improve global treatment accuracy, especially for helical deliveries.

Research partially sponsored by Tomotherapy Incorporated
SU‐FF‐T‐411: Boundary Study of Bragg Peak Shift and Bragg Peak Degradation in Proton Dose Calculation
Authors: Chen W , Liu Y , Guo B , Jette D , Papanikolaou N
Published: April 2010

Purpose: The purpose of this work is to study the Bragg peak shifts and degradation caused by density and boundary changes in proton beam dose calculation Method and Material: Proton beam delivery provides promising dose characteristics as radiation dose can conform tightly to tumor while sparing surrounding healthy tissues. Proton particles deposit energy in a narrow range around the Bragg peak and as such the dose calculation is more challenging for that the Bragg peak is sensitive to tissue density, tissue composition and organ boundaries along the proton track path. We simulated a few scenarios to study the proton Bragg peak shift due to density and Bragg peak degradation due to change and boundary changes. The calculation of the three dimension dose matrix was performed using a 2 × 2 × 1 mm3 voxels in the depth peak dose range in water phantom after some rough simulation for the dose peak estimation. Results: Bragg peak shift at the iso‐center slice were found to follow a linear relationship with the density of heterogeneity insert based on our simulations with density ranging [0.4 2.0] g/cm∧3 which we studied. Bragg peak degradation and proton dose changed significantly due to low density and small beams size. Proton dose degraded when high energy proton beam irradiated to low density material. Proton dose degraded also when small beam with beam radius at several mm range. Conclusion: Proton dose calculation depends on many factors as Bragg peak is sensitive to tissue density and composition. Besides that, there exist several scenarios causing Bragg peak shift due to density change, causing Bragg peak degradation due to low density and small proton beam. The Monte Carlo simulation is a very accurate solution to provide precise dose distribution in inhomogeneous structures by simulating transport and energy deposition.
SU‐FF‐T‐416: Antiproton Therapy: A Simplified Method to Characterize and Compare Dose From Peripheral Radiation Fields
Authors: Keyes RW , Luan S , Holzscheiter M
Published: April 2010

Purpose: Recent work has shown the potential benefits of antiprotons for radiotherapy. Because of the large amount of energy released by the annihilation of antiprotons, it is of interest to understand the dosimetric properties of the peripheral field. The purpose of this research is to develop a standard method to estimate, characterize, and compare the secondary dose in the peripheral radiation field of particle beams, allowing for the assessment of relative safety and treatment suitability for a given patient. Method and Materials: The FLUKA 2008.3 Monte Carlo package was used. A simplified set of target and secondary tissue phantoms (1 cm diameter spheres) were placed in a volume of water, with secondary phantoms placed every 10 cm out to 100 cm along the beam axis and perpendicular to the beam axis at the depth of the target. The target phantom was irradiated by a pencil beam of particles (antiprotons, protons, etc.). Absorbed dose was evaluated in the target phantom and ambient dose equivalent (H*(10)) was evaluated in the secondary phantoms using factors from ICRP 74 and Pelliccioni to convert from fluence. This data was then used to determine the ratio of H*(10) to target absorbed dose. Additionally, the relative contributions by different particles to the H*(10) were measured as well as various particle fluence spectra. Results: 2–40 million primary beam particles yielded satisfactory statistics to estimate the peripheral field dose values for beams of antiprotons and protons. Conclusion: As awareness of second cancer risk grows, a standard scheme for estimating secondary dose from particle therapy will be all the more important. Our scheme allows for detailed characterization of the peripheral field and dose estimation can be made for non‐target organs by weighting dose with tissue factors.
SU‐FF‐T‐418: Development of An Easy to Commission Electron Beam Model Using Highly Accurate Fluence Benchmarks From Full Monte Carlo Treatment Head Simulations and Measurements
Authors: Hirscht J , Faddegon B
Published: April 2010

Purpose: Development of an easy to commission electron beam model using highly accurate fluence benchmarks from Monte Carlo treatment head simulations and measurements. Method and Materials: A simple electron beam model consists of the key treatment head components: a circular primary source for electrons, a disk representing the secondary scattering foil and a ring representing the monitor chamber sidewall. The primary source accounts for scatter in the exit window and primary foil. The angular distribution of the primary source is chosen to match the lateral dose profiles from measurements with only the primary foil in the treatment head. The energy spectrum is derived from unfolding measured depth dose curves from large fields. The angular distribution of the primary source is broadened analytically using accurate scattering theory to account for the secondary scattering foil. The lateral extent of the beam is restricted to account for the collimation by the sidewall of the monitor chamber. Phase space data generated from the simple electron beam model is used with the EGSnrc user code BEAMnrc to simulate the secondary collimators and scattering of the electrons in air. Results: Primary foil simulations with the beam model, with no secondary scattering foil or monitor chamber in the beam line, match measured dose profiles of large fields within 1%–2%. Fluence profiles were in comparable agreement with the benchmark. Energy spectra were cleanly unfolded from measured depth dose curves from large fields. Peak energy was within 0.05 MeV of the fluence benchmark. Preliminary results for the full clinical beam with the secondary foil and chamber in place are promising. Conclusions: The influence of the different treatment head components on the beam were accurately determined with the detailed fluence benchmarks, which proved instrumental in development of this beam model. Research sponsored by NIH R01_CA104777.
SU‐FF‐T‐433: Reducing the Simulation Time of a Prostate Cancer Clinical Setup by Two Orders of Magnitude
Authors: Yepes P , Randeniya S , Taddei P , Mirkovic D , Newhauser W
Published: April 2010

Purpose: Demonstrate the feasibility of utilizing the Fast Dose Calculator (FDC), a track repeating algorithm, for the simulation of a clinical proton radiotherapy setup including: beam nozzle with range shifter, aperture, range compensator and patient geometry. Methods and Materials: A database of discretized proton trajectories in water was generated with GEANT4. Information about the energy deposited, length and direction is stored for each trajectory step. Proton trajectories in any other material are extrapolated from the database by scaling step lengths and angles. Scaling parameters for various materials are obtained by comparing GEANT4 doses in the various materials to those obtained from FDC by scaling the trajectories in water. FDC allows for arbitrary geometry descriptions based on the geometry package of ROOT. The voxelized geometry from a CT‐scan of a patient being treated for prostate cancer was used to simulate the dose deposited by a passively scattered proton beam. A beam defining aperture and a range compensator were included in the simulation. This setup was used to calculate the dose distribution produced by a proton beam defined by the phase space at the front‐end of the aperture. In a second set of simulations a simplified version of a nozzle was included. In both cases the results were compared with a GEANT4 full simulation. Results: Doses calculated with FDC and GEANT4 were compared using the Gamma function. The comparison showed good agreement with less than 1% of the voxels with values above unity. FDC was found to be more than one hundred times faster than GEANT4. Conclusions: A fast track repeating algorithm has been tested in complex and realistic geometries for proton therapy. The algorithm preserves adequate accuracy and reduces calculation times by more than two orders of magnitude. Research Sponsored by the Gulf Coast Center for Computational Cancer Research.
SU‐FF‐T‐437: Improving the Efficiency of Monte Carlo by Using Systematic Sampling in Phase Space Reconstruction: Feasibility Study
Authors: Fan J , Li J , Xu Q , Fourkal E , Jin L , Wang L , Price R , Ma C
Published: April 2010

Purpose: Generalized source model is effective in characterizing the radiation source for the implementation of Monte Carlo dose calculation. The purpose of this research is to investigate a systematic sampling method in source phase space reconstruction to reduce uncertainty of the MC dose calculation. Method and Materials: As a computer random sampling method, MC introduces statistical uncertainties in each random sampling step during simulation. Uncertainty of final result can be reduced by reducing the sampling uncertainty in any of the step. In our study, a systematic sampling method was used to reduce the uncertainty in source phase space reconstruction. The basic idea of the systematic sampling is to divide the sampling range into small intervals and sample from each interval. For a distribution f(x), a⩽x⩽b. instead of sampling x between a and b, we divide the space between a and b into small intervals: d1⩽d2⩽d3⩽……⩽dn, where d1=a, dn=b, and sample x from each interval with a new distribution fi(x). Results: Particle energy and location sampling in phase space reconstruction have been tested using the systematic sampling. For particle location sampling from a 10×10 cm2 field, the field was divided into 100 small units and N/100 particles were uniformly sampled from each unit. The sampling uncertainty was reduced to 1/10 compare to the direct sampling and a more uniform distribution was found in a 2D distribution map. For particle energy sampling, energy distribution was divided to N bins from the minimum energy to the maximum. Number of particles sampled from each bin depends on the probability density. There is no fluctuation in dose contribution if particle energy were sampled using the systematic method. Conclusion: Phase space reconstruction from the source model using the systematic sampling can significantly reduce the sampling uncertainty and therefore can reduce the uncertainty in MC dose calculation.
MO‐FF‐A3‐06: Preliminary Feasibility Study: Modeling 3D Deformations of the Prostate From Whole‐Mount Histology to in Vivo MRI
Authors: McNiven A , Moseley J , Langer DL , Haider MA , Brock KK
Published: April 2010

Purpose: To investigate the accuracy of a 3D biomechanical model‐based deformation algorithm (MORFEUS) in modeling the prostate deformation that occurs between in vivo magnetic resonance imaging (MRI) and identification of the tumor on whole‐mount histology. Method and Materials: Three image sets were acquired for 10 patients: 1) in vivo T2‐weighted MR images acquired prior to prostatectomy, 2) ex vivo T2‐weighted MR images, and 3) digital images of the histological slices, rigidly registered to construct a 3D volumetric image. All three images sets were imported into the radiation treatment planning system for contouring. The entire prostate gland, the peripheral zone and central gland were contoured. The prostate was converted into a finite element model, where each zone was assigned the appropriate material property. Naturally occurring structural and morphological features (e.g. urethra) were identified as verification points in the in vivo, ex vivo, and histological images, for quantification of the accuracy of the deformable registration. MORFEUS was used to model the deformations that occur due to excision and fixation either directly, deforming histology to in vivo MRI, or using a two‐step process, histology to in vivo MRI via an intermediate step, using ex vivo MRI. Results: Initial analysis has been completed for a subset of the patients. Uncertainties following rigid registration alone exceeded 8.0mm. No significant improvements were observed when including the intermediate deformation step. The average absolute error following deformable registration, based on the verification points, was 1.3, 1.2, and 1.9mm in the left/right, anterior/posterior, and superior/inferior directions, respectively. This error is smaller than the 3 mm image slice thickness. Conclusions: Substantial deformation confounds the ability to compare histology with in vivo imaging. Deformable registration using MORFEUS can be used to resolve the deformation, enabling quantitative evaluation of in vivo imaging based on histology as a gold standard for tumor definition.
TU‐E‐304A‐03: Does New Lightweight Leaded Eyewear Provide Adequate Radiation Protection for Fluoroscopists?
Authors: Schueler B , Sturchio G , Landsworth R , Hindal M , Magnuson D
Published: April 2010

Purpose: Leaded eyewear is commonly recommended for physicians routinely performing interventional fluoroscopy procedures. However, radiation‐attenuating glasses and goggles can be heavy and uncomfortable. Recently, several new lightweight eyewear designs have become available. Two such designs were investigated to determine how well they are able to reduce eye dose under clinical conditions. Materials and Methods: The eye dose was measured using OSL nanodot dosimeters positioned on a Rando head phantom. The phantom was positioned next to an acrylic phantom to duplicate the position of an operator exposed to scattered x‐rays. Eye dose was measured with and without leaded eyewear in three different positions: head directed toward the scatter volume and angled 45 and 90 degrees. The eyewear investigated included standard style glasses with 0.75 mm lead equivalent lenses (Type A), sport‐wrap glasses with 0.75 mm lead equivalent lenses (Type B) and a panorama shield with 0.07 mm lead equivalent acrylic lenses (Type C). Results: With the phantom head directed toward the scatter volume, the eye dose was reduced by 90%, 88% and 61% for Type A, B and C, respectively. Each value is lower than expected from the attenuation of the lenses alone, indicating backscatter is a significant contribution. At 90 degrees, eye protection dropped somewhat for Type A (75%), significantly for Type B (31%), while remaining the same for Type C (61%). The poor protection afforded by Type B at 90 degrees was primarily due to limited side coverage. Conclusion: Even though the lead equivalent thickness of Type C is much lower than other designs tested, increased side coverage resulted in nearly equivalent eye dose reduction when side exposure was predominant. The use of 0.75 mm lead equivalent lenses appears to have diminishing returns given that backscatter and side exposure are a significant source of eye exposure.
WE‐D‐210A‐03: Systems and Probes for Ultrasound Molecular Imaging
Authors: Ferrara K , Hu X , Zhang H , Stephens D , Kruse D
Published: April 2010

Specialized ultrasound systems and targeted microbubbles optimized for vascular molecular imaging continue to advance. The development of methods for sensitive and selective imaging of adherent, targeted contrast agents requires improvements in both the physical systems and probes. We have developed transducers and signal processing techniques to maximize transducer bandwidth and integrated the components with a clinical ultrasound scanner. The transducer integrates low and high‐frequency arrays; the center‐row high‐frequency array is surrounded on each side with confocally‐focused low‐frequency arrays. By transmitting from the low‐frequency (1.6 MHz) arrays and receiving through the high‐frequency (7 MHz) array, harmonic microbubble echoes can be detected and distinguished from the surrounding tissue. Further, by combining echoes over a pulse train, a targeted agent to free agent signal ratio of 15∼22 dB can be obtained without waiting for agent clearance. Further, we report on radiolabeling methods to fully assess microbubble biodistribution with and without molecular targeting or insonation. We find that microbubbles are rapidly accumulated within the liver and spleen, although a small (but significant) mass of the microbubble shell accumulates as a result of local insonation.

We acknowledge the support of NIH CA 103828 and CA 112356.
WE‐E‐BRD‐02: Development of a Software for Integrating the Medical Accelerator Model with Patient Phantoms Into Monte Carlo Based Dosimetry Platform
Authors: Ding A , Han B , Xu X
Published: April 2010

Purpose: To develop a new software package that integrates the detailed medical accelerator model with anatomically‐realistic phantoms in the Monte Carlo engine, MCNPX, for the determination of secondary organ doses from secondary photons and neutrons during the treatment. Method and Materials: The accelerator models were developed include 80 MLC leaves, two pairs of tungsten jaws operating at 6 and 18 MV, respectively. The Pregnant Women, Adult Male and Adult Female phantoms were utilized. The software was designed in the Visual C♯.NET and the preliminary effort was on the graphic user interface (GUI) to automatically generate the MCNPX input deck consisting of accelerator and patient according to user‐defined treatment plans. The MLC configuration files were parsed to collect positions of the jaws and MLCs before they were exported into MCNPX by using the “TRCL” with the “LIKE BUT” card. Results: A number of user‐friendly GUI features have been developed for a user to select treatment parameters: selection of an accelerator type, a type of phantom, specify the phantom origin position and the field numbers, parse in the MLC configuration files and save the MLC leaf positions. According to the positions of the jaws and MLCs, the software can automatically output the MCNPX deck files, classified per field, per segment and per MLC leaf position with the accelerator model and computational phantoms. Conclusion: A new software has been demonstrated. The preliminary results indicate that the GUI design and integration features are feasible and versatile. This software is designed to help a user to carry out organ dose studies using the MCNPX input deck without having to handle complex accelerator and phantom information. Such a tool can facilitate the study for assessing and for comparing various new modalities in terms the likelihood for secondary cancer induction.
WE‐E‐BRD‐03: Re‐Evaluation of the Product of W/e and the Graphite to Air Stopping Power Ratio for Co‐60 Air Kerma Standards
Authors: Thomson RM , Rogers D
Published: April 2010

Purpose: To reanalyze experiments which determine , the product of (W / e)air, the average energy deposited per coulomb of charge released in dry air, and , the Spencer‐Attix mass collision stopping‐power ratio for graphite to air, and to calculate an average value for this product for the BIPM air kerma standard: . This value could be adopted for use with air kerma primary standards, along with corrections to account for variations due to cavity size. Methods and Materials: The experiments measured by various methods, often involving calorimeters and ionization chambers. Correction factors, e.g., to account for gaps about a calorimeter core or perturbations due to a cavity's presence, are calculated as needed for each experiment using the EGSnrc user‐codes CAVRZnrc, DOSRZnrc, and CAVITY. Stopping power ratios are evaluated using SPRRZnrc for different choices of graphite density (bulk 1.70 g/cm3 or grain 2.265 g/cm3) for the density effect correction and average excitation energy for graphite (I=78 or 87 eV). For each experiment, the corrected value of is multiplied by , the quotient of the stopping power ratios for the BIPM chamber and the experiment in question. A least squares technique is used to compute an average value of . Results: The correction factors generally decrease the value of for each experiment, often outside the range of one standard deviation quoted with each experimental result. The ratio varies by less than 0.1% for different choices of density correction and I‐value and hence the product is also relatively insensitive to these choices.

Conclusion: The preliminary analysis suggests that the accepted value of , 33.97 J/C ±0.15%, is 0.6% too high. This would have implications for primary air kerma standards worldwide and for the value of (W / e)air which is used in low energy x‐ray standards.
WE‐E‐210A‐02: Emerging X‐Ray Fluoroscopic Guidance Technologies for Challenging Cardiovascular Interventions
Authors: Speidel M
Published: April 2010

X‐ray fluoroscopy remains the primary guidance modality for cardiac interventions due to its appealing combination of real‐time imaging, high spatial resolution, simplicity of use, and compatibility with conventional catheter devices. However fluoroscopy has well‐recognized limitations. The lack of depth resolution and poor soft tissue contrast in an x‐ray projection make it difficult to precisely position devices with respect to target cardiac structures. Ionizing radiation dose is an ongoing concern, particularly for interventions with long imaging times such as catheter‐based electrical mapping and ablation of atrial fibrillation.

Technologies which reduce dose and add three‐dimensional context to the live fluoroscopic image offer a route towards overcoming these limitations. Scanning‐beam digital x‐ray (SBDX) is an inverse geometry fluoroscopic system that provides both dose reduction and real‐time tomosynthesis, a feature that can be exploited for image‐based 3D tracking of catheter electrodes. The operating principles of SBDX will be reviewed and recent investigations of 3D catheter tracking based on multiplanar tomosynthesis will be presented. Fusion of live fluoroscopy with roadmaps derived from pre‐acquired 3D image data (e.g. CT, MRI) can allow the interventionist to visualize structures lacking x‐ray contrast, or to perform novel therapies targeted to the physiologic status of cardiac tissue. A fluoroscopic fusion system for recanalization of chronically occluded arteries and for targeted stem cell therapy will be discussed.

This lecture will provide an overview of the demands and constraints of fluoroscopically‐guided cardiovascular interventions, dose reduction and 3D catheter tracking capabilities enabled by the SBDX system, and clinical application of fluoroscopy fused with 3D roadmaps.

This research was supported in part by NovaRay Medical, Inc. and NIH/NHLBI.

Learning Objectives:

1. Review the demands and constraints of fluoroscopically‐guided interventions

2. Understand the principles of SBDX dose reduction and 3D catheter tracking

3. Discuss x‐ray fluoroscopy combined with 3D imaging for cardiovascular interventions
TH‐A‐211A‐01: Digital Tomosynthesis for Target Localization
Authors: Yin F , Wu Q , Godfrey D , Ren L , Yoo S , Maurer J , Yan H
Published: April 2010

Any deviation between treated and planned volumes for 3‐D conformal therapy, such as IMRT, may cause an adverse clinical outcome. It is therefore critical to minimize all potential deviations using an on‐board (or real‐time) imaging procedure immediately prior to radiation delivery. At present, conventional 2‐D radiographic imaging and state‐of‐the‐art 3‐D cone‐beam CT (CBCT) are typically employed for treatment verification. However, 2‐D radiographic verification is mainly based on bony structures and/or implanted fiducials, and is sub‐optimal for soft‐tissue targets. While on‐board CBCT can provide 3‐D soft tissue information, it has three potential limitations: 1) The acquisition time is limited to a minimum of 60 seconds (≈15 breathing cycles) for on‐board CBCT, making single breath‐hold imaging impractical for organs which exhibit respiratory motion; 2) 360° mechanical clearance for CBCT acquisition may limit the use of CBCT for large patients, those with tumors at peripheral locations (e.g. breast), or those with substantial immobilization or support devices; 3) A high radiation dose (2–9 cGy) is delivered to the imaged volume with current imaging techniques, which is undesirable for daily imaging and may be a particular problem for those who are at high risk of developing second malignancies. To overcome these limitations, innovative digital tomosynthesis (DTS) imaging technologies are being developed for 3‐D and 4‐D target localization.

Although DTS technology has been used for digital chest and mammography, its use in target localization is new. DTS only requires limited gantry rotation (e.g., a scan angle of 40° or less) to reconstruct 3‐D anatomic information. Thus, imaging time and dose are substantially reduced compared to CBCT, making breath‐hold DTS a simple solution for daily imaging of moving organs. 4‐D DTS can also be generated much faster than 4‐D CBCT, which is desirable for on‐board 4‐D tomographic imaging. Further, the reduced mechanical clearance needed for DTS makes it more widely applicable than CBCT. At present, limited information has been published regarding the fundamentals of DTS for target localization, and/or preliminary clinical DTS localization results. The purpose of this presentation is to provide updated information about these topics, including the following objectives:

1. To understand the technical challenges and clinical potentials of using DTS technologies for target localization in radiation therapy

2. To understand the latest developments in DTS reconstruction and registration methods

3. To understand the clinical feasibility and efficacy of kV DTS compared to kV CBCT

4. To learn about the latest developments in MV DTS and brachytherapy DTS applications

Work is partially supported by grants from NIH, Varian Medical Systems, and GE Health Care.
TH‐B‐303A‐01: Diffusion Imaging: What It Can Tell Us About Cancer
Authors: Yanasak N
Published: April 2010

The use of the self‐diffusion characteristics of water to generate image contrast for magnetic resonance imaging (MRI) can provide a wealth of information about tissue microstructure. Diffusion imaging has demonstrated sensitivity to pathology in structured tissues (e.g., white matter, cardiac muscle fiber, kidney), where the structure may be altered. Additionally, the relative volume of water between intra‐ and extra‐cellular compartments, as well as the permeability of tissue membranes dividing the compartments, may be affected by certain diseases. Cancer, in particular, affects water diffusivity in a number of ways. In tumor regions where a high density of cells exists, the diffusion of extra‐cellular water can be more restricted than healthy tissue. In regions where the tumor has become necrotic or cystic, diffusion is less restricted. Tissue structure may not be affected equally in all directions. Invasiveness of cancer into neural fibers in the brain, or their preservation and displacement around a tumor, will exhibit differences in diffusion magnitude as well as direction of restriction. Finally, therapeutic intervention (radiation therapy or chemotherapy) of cancer can be monitored using diffusion techniques, where increases in diffusion within a tumor may suggest the efficacy of treatment.

This presentation will provide a survey of different diffusion MRI techniques, focusing in particular on when they may be helpful in the diagnosis and treatment of cancer.

Learning Objectives:

1. To describe how biological changes in tissue correlate with diffusive behavior of water.

2. To provide a simple picture of cancer and the different ways in which it can alter cellular diffusion characteristics.

3. To give an overview of the different diffusion imaging techniques in MRI: How do they work? What information do they provide? Under what contexts are they important in the diagnosis of cancer?
TH‐B‐210A‐01: Determination of Dose to Individual Patients in Radionuclide Imaging Procedures Including Planar, SPECT, and PET
Authors: Williams L
Published: April 2010

Individual patient absorbed dose estimates are a relatively novel feature in nuclear medicine physics. Historically, almost all estimates were made using phantoms having predetermined geometries and organ sizes. Yet none of their various geometries may be suitable for a given person and other methods are being implemented to allow patient‐specific dose computations. For either phantom or patient‐based estimates, target organ dose is given by the matrix product: D (target organ) = S * Ã (source organs). In the equality, the rectangular matrix S depends upon the energies of emission, their probabilities and the geometry of either the phantom or patient. Ã is a vector containing elements which are the total decays from each source organ. Total decay means essentially an integral over the activity A(MBq) in that source over the time interval 0 ⩽ t ⩽ 8. For an individual, S can sometimes be determined using manipulations of a phantom value for a given radionuclide. In a pure beta or alpha emitter, S becomes diagonal and its elements are proportional to the inverse of the organ mass. This situation is common in targeted radionuclide therapy (TRT) and is the most important application of patient‐specific dose. If the radionuclide emits significant photon radiation, a Monte Carlo approach is probably required to estimate individual organ doses. If one does not correct for target mass, errors in S can approach factors of two to three. This becomes particularly important in some clinical conditions such as lymphoma where the splenic mass may become very large. Determination of Ã is based on measuring activity (A) at‐depth in the patient. At least six techniques are in the literature for activity quantitation. The simplest is single probe counting with corrections for distance such as using inverse‐square law for surface structures. This method, however, cannot be used at‐depth in the patient. Geometric‐mean gamma camera imaging is the most common method of activity quantitation, but suffers from overlapping source organs. Its accuracy is on the order of +/− 30% in phantom and animal studies. The most advanced camera technique is quantitative SPECT imaging. This measurement (QSPECT) is ideally done with hybrid SPECT/CT scanners. Corrections are made for attenuation, scatter, collimator geometry and partial volume effects. Absolute activity accuracy approaches +/− 5% in QSPECT. PET imaging can be competitive with this result if a positron emitter of sufficient half life and emission probability is available for labeling. The ultimate dose uncertainty for a given patient is a quadratic combination of errors due to S and Ã.

Learning Objectives:

1. Understand use of D = S*Ã for internal emitters.

2. Realize that patient‐specific doses are obtainable.

3. Know the sizes of uncertainty in activity and S measurements.

4. Discover the use of QSPECT and quantitative PET.
TH‐C‐BRD‐09: Experimental Determination of Central‐ and Off‐Axis Scerma Using Scatter Primary Ratio
Authors: Wang K , Zhu T
Published: April 2010

Purpose: The absorbed dose for a clinical megavoltage photon beam can be separated into primary and scatter doses expressed as a convolution of the point spread kernels with Terma (T). This expression requires an additional beam hardening function to account for the difference of photon attenuation vs. energy for the photon energy spectrum. It has been established that the beam hardening function can be eliminated if one rewrite the convolution as modified polyenergetic energy deposition kernels with primary collision Kerma Kc, and Sc, Scerma, equal to T‐ Kc. Both Kc and Sc include beam‐hardening effects but are with different depth dependence. However, no experimental method has been established to determine the depth dependence of Sc. In this study, we focused on developing a method to experimentally determine Sc/Kc at central‐ and off‐axis. Methods: We use an empirical expression for scatter‐to‐primary ratio (SPR) as a function of photon energy to determine Scerma at infinite field size and depth. There are three parameters, a0, w0 and d0, related to SPR, which need to be determined experimentally, and they can be directly correlated with attenuation coefficient μ. Therefore, one can determine central‐ and off‐axis scerma, if μ is known. To confirm the off‐axis Scerma we obtained from the off‐axis μ(x), we propose an independent experiment to extract off‐axis SPR. The SPR will be determined by fitting experimentally‐measured TPR *Sp. Results: We have extracted the parameters from Monte Carlo simulated data at central axis in a wide clinical energy range. We find that a0/w0 is proportional to the beam energy at central axis, and this is the slope of the depth dependence of Sc/Kc. Our results also show that the ratio of primary Scerma‐to‐collision Kerma has linear depth dependence. Conclusion: Experimental method is developed to determine the off‐axis Scerma, which is critical in convolution‐based scatter dose calculation.
TH‐C‐BRD‐10: A Simple Approach for Optimal Field Abutment in Modulated Electron Radiation Therapy
Authors: El Dib A , Jin L , Fan J , Li J , Sherbiny N , ELGohary M , Ma C
Published: April 2010

Purpose: Our aim is to address the problem of unacceptably large dose variations at the junction of two adjoined fields in modulated electron radiation therapy (MERT) by optimizing the gap separation at the junction area. Another aim is to provide basic knowledge helping the optimization to get the best MERT plan and understanding the upper limitations for the future MERT treatment design. Material and method: In this work we used MCBEAM and MCSIM codes for accelerator simulation and phantom/patient dose calculation, respectively. A prototype manually driven eMLC was accurately modeled. Simulation results were compared to measurements. Dose distributions inside a phantom for two adjoined electron fields were investigated for different gaps and different electron energies. Gaps were then evaluated by achieving the best dose distributions and the sharpest target DVH curve fall‐off. The gap sizes, which gave the best dose distributions and DVHs for all the energies available, were determined. Gap sizes as a function of energy and SSD to achieve optimal dose profiles at desired depths in the phantom was also studied. Results: It is shown that as energy increases the gap size need to increase which may be ascribed to the change in penumbra. For a given energy, the gap size shows a linear relationship with the SSD. As is expected, the optimal gap is larger with larger SSD and higher energies. A series of empirical formulas have been developed in obtaining the optimum gap sizes for the adjoined beams with different energies, which can improve the target dose uniformity significantly. Conclusion: For each electron beam energy an optimal gap can be chosen to minimize the dose inhomogeneity arising from adjoining two electron fields, which will facilitate the design of the leaf sequences for MERT dose delivery using an eMLC.
TH‐C‐BRC‐03: An Image‐Guided Micro‐Radiotherapy System Based On Carbon Nanotube Field Emission Technology for Small Animal Irradiation for Cancer Research
Authors: Wang S , Schreiber E , Calderon‐Colon X , Peng R , Sultana S , Zhang J , Zhou O , Chang S
Published: April 2010

Purpose: To demonstrate the feasibility of a nanotechnology‐based micro‐computed tomography (micro‐CT) and micro‐radiotherapy (micro‐RT) integrated system (micro‐CT‐RT) that delivers real‐time image‐guided intensity‐modulated radiation therapy (IMRT) for small animal irradiation. Materials and Methods: Carbon nanotube (CNT) field emission (FE) based x‐ray technology is used for the development of the multi‐pixel x‐ray beam array micro‐RT system. The multi‐pixel x‐ray beam array has individual pixel control to electronically shape the radiation field and form intensity modulation patterns in the irradiated object. Monte Carlo based dosimetric simulations and electro‐optical simulations have been performed to guide the micro‐RT system design. Results: A prototype multi‐pixel beam array micro‐RT system was designed and fabricated. The prototype can successfully generate a 5 × 10 x‐ray beam array which offers a maximum radiation field size of 10 mm x 20 mm . Each beam can produce a dose rate on the order of 1 Gy/min at the center of the irradiated object. Conclusions: The feasibility to fabricate a multi‐pixel beam array micro‐RT system based on CNT FE technology is demonstrated. The prototype micro‐RT can generate a 5 × 10 x‐ray beam array which offers a maximum radiation field size of 10 mm × 20 mm in the irradiated object. The system is still under testing and performance improvement. Once fully developed, the micro‐RT system will be integrated with the nanotechnology‐based prototype micro‐CT already developed for real time image‐guided IMRT and treatment response observation in small animals.
TH‐C‐BRC‐10: Evaluation of a Micro‐CT Based 3D Conformal Animal Radiotherapy System
Authors: Zhou H , Xu J , Rodriguez M , van den Haak F , Zhu X , Xian Y , Nelson G , Jogani R , Keall P , Graves E
Published: April 2010

Purpose: To treat small animal disease models with clinically‐relevant radiotherapy strategies, an image‐guided 3D conformal radiotherapy system based on a microCT imaging device has been constructed. Method and Materials: A variable‐aperture collimator was installed in a GE RS120 microCT, so that the beam width could be adjusted between 0 to 100 mm at the CT isocenter. The collimator was aligned with the X‐ray beam axis through film and detector measurements. A two‐dimensional translation stage was integrated with the existing z‐stage of the scanner to allow 3D positioning of a subject within the CT bore. Radiation treatment planning software is based on the RT_Image application, including tools to specify treatment parameters based on the CT image and an EGSnrc‐based Monte Carlo dose calculation package. To test this system, two mice with spontaneous lung tumors have been irradiated to a dose of 2 Gy. Results: Automation of the system has been realized through high‐precision mechanical design and assembling of the collimator and stage, the calibration, and the control software. Geometric and dosimetric calibration of the system has resulted in beam width and position precisions better than 0.1 mm, and dose precision better than 3%. The treatment planning software development can specify treatment parameters within the coordinate frame of the CT image, which can then be used to control the device hardware. Mice with lung tumors were irradiated with the system. Post‐mortem immunohistochemical assays demonstrated the presence of DNA double strand breaks within the radiation target. Conclusion: We have demonstrated the accuracy and utility of a novel microCT‐based image‐guided 3D conformal radiotherapy system. Clinically‐similar image‐guided radiation therapy has been applied to small animals, facilitating future investigations of this technology in the laboratory.
TH‐C‐303A‐06: Performance Characterization of a MVCT Scanner Using Multi‐Slice Thick, Segmented Cadmium Tungstate‐Photodiode Detectors
Authors: Kirvan P , Rathee S , Monajemi T , Fallone B
Published: April 2010

Purpose: To evaluate the performance of a MVCT system based on multi‐slice, thick, and segmented cadmium tungstate‐photodiode detectors. Method and Materials: Our MVCT's detector is a 2D array of 1mm × 1mm (pitch) × 10mm (thickness) cadmium tungstate crystals separated by a septa paint of reflectivity higher than 0.975. The scintillators are mounted on ten 16 × 16 element photodiode arrays (SCA‐CA256ES, Semicoa, Costa Mesa, CA). The total array size is 320 detectors along the arc by 16 detectors along the slice thickness direction. The radius of curvature of detector arc is 92.5cm. In our system, the source and detectors remain stationary while the object being imaged is placed on a precision rotating stage. Due to the high dose per pulse provided by our clinical linac, it is not possible to image a test object with a dose of < 50cGy in a 6MV beam. In order to obtain low dose images, we used the small amount of Bremsstrahlung radiation produced in the scattering foils in 6 MeV electron beam after removing the electrons from the beam by placing 4cm of solid water in the beam. Results: Our system demonstrates a uniformity index of 0.4% at 1.9cGy. The noise standard deviation is around 2% at 1.9cGy. CT number linearity (R2= 0.9982) and low contrast resolution (15 mm object with 1.5% contrast at 2 cGy) are superior to published evaluations of commercially available tomotherapy MVCT. The spatial resolution is about 4lp/cm which is limited mainly by the diffused Bremsstrahlung source. Conclusion: Thick segmented cadmium tungstate detectors offer significantly better low contrast resolution per unit dose at MV energy than commercially available gas filled or flat panel detectors. This work demonstrates the feasibility of creating a fully functional MVCT system using this technology.
TH‐C‐304A‐06: Assessment of Registration Accuracy in 3D Transrectal Ultrasound Images of Prostates
Authors: Karnik V , Bax J , Cool D , Gardi L , Gyacskov I , Montreuil J , Romagnoli C , Fenster A
Published: April 2010

Purpose: To evaluate the accuracy of our rigid and non‐rigid registration methods to align three‐dimensional (3D) transrectal ultrasound (TRUS) images of the prostate in order to improve repeat biopsy planning and guidance for prostate cancer diagnosis. Methods and Materials: Three 3D prostate ultrasound images were obtained from each of the 16 patients during 3D prostate ultrasound‐guided biopsy procedures. These 3D images had identifiable calcifications and cysts, which were used as fiducials for the registration validation. For each prostate, images at two different time points (to and t1) during the procedure were selected and the 3D coordinates of the identified fiducials were recorded. A total of 62 fiducials were identified. All images were then segmented manually and semi‐automatically. Images at to were registered to the corresponding images at t1 using rigid and non‐rigid registration. Rigid and non‐rigid registration was performed using boundary‐based iterative closest point and thin‐plate spline algorithms, respectively. We evaluated the registration methods by determining the target registration error (TRE), effect of segmentation variability on registration variability, the TRE dependence on fiducial distance from the transducer tip, and the fiducial localization error (FLE). Results: Tests showed that the FLE was 1.3mm. The mean TRE for manual and semi‐automatic segmentation was 2.2mm and 2.3mm respectively in both rigid and non‐rigid cases. There was little correlation between the TRE and the distance of the fiducials from the ultrasound transducer tip, and segmentation variability resulted in a 0.57mm standard deviation of the TRE. Conclusions: Our results suggest that both rigid and non‐rigid registration techniques for 3D TRUS images during a biopsy procedure are accurate to within 2.3mm, which is less than the 5mm radius of the smallest tumors considered clinically significant. Future tests will evaluate registration accuracy for multimodal cases, specifically magnetic resonance to ultrasound images.
TH‐C‐210A‐03: X‐Ray Based Imaging in Neurovascular Intervention — Requirements and Challenges
Authors: Wakhloo A
Published: April 2010

In the US, 795,000 people are expected to have a new or recurrent stroke in 2009. Ischemic stroke, which accounts for more than 80% of all strokes, carries a severe toll being the 3rd cause of death and the leading cause of disability. The cost of stroke, both direct and indirect, will exceed $60 billion this year alone. Hemorrhagic stroke on the other hand originates from rupture of brain aneurysms, which cause the vast majority of subarachnoid hemorrhage, a devastating medical emergency that affects more than 30,000 Americans each year and causes substantial disability and death.

As in the coronary and peripheral vascular system, surgical treatment and medical management is progressively replaced by minimally invasive endovascular treatment. In recent years we have witnessed a rapid advancement in stent and stent‐like technology. Stents do not only serve for a combined intra‐ and extrasaccular treatment of challenging aneurysms, but assist the revascularization in acute and chronic ischemic conditions of the neurovascular system. In the Neuroangiography Suite x‐ray based imaging for guidance of devices and for monitoring brain perfusion during the intervention has experienced a quantum leap. Replacement of Image Intensifiers (II) with Flat Panel Detectors (FD) has enabled to increase the rotational speed of the system and its use as cone beam CT. Today angiography techniques do not only serve to characterize local flow alterations induced by vessel implants, but also study brain perfusion prior and during revascularization maneuvers. Detailed information of vascular structures is provided in conjunction with the surrounding brain tissue and vessel wall. Imaging of temporary or permanent implants is available with high resolution that is vital for a precise placement, treatment efficacy and patient safety.