bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐A‐201C‐02: Registration Methods in Multi‐modality Imaging
Authors: Kapoor A
Published: August 2010

The value of image processing and fusion of different imaging modalities has been analyzed for both diagnostic and prognostic purposes ‐ less so for interventions. There are numerous technical approaches for registration and image fusion of radiological images to consolidate imaging data from different modalities. Registration is defined as aligning the two data sets spatially to each other where as fusion refers to overlaying and visualizing these merged sets.

In the case of imaging data sets of fixed or rigid organs such as the spine or brain these algorithms are well studied and the results generally more robust and computationally fast. But the problem is more difficult in organs with physiologic motion and non‐rigid organs. Furthermore image‐to‐image registration from different modalities increases the complexity of the problem. Issues related to strengths and disadvantages of different techniques and how different imaging modalities impact these algorithms will be discussed. The details and implementation of translating these techniques from the research bench to clinical application will be presented.

This lecture will provide an overview of the different algorithms that have been studied for registration of imaging datasets challenges and limitations of practical implementation and use cases in clinical scenarios.

Learning Objectives:

1. Understand the concept of registration and image fusion.

2. Understand the issues and trade‐offs between different registration algorithms in relation to various imaging modalities.

3. Understand the issues in translating these to clinical application.
TH‐B‐201C‐01: Nuclear Medicine Accreditation Acceptance Testing and Annual Surveys
Authors: Botti J
Published: August 2010

With the passing of the Medicare Improvements for Patients and Providers Act (MIPPA) MIPPA requires facilities that are billing for these services under Medicare B to be accredited by January 1 2012. CMS has recognized the American College of Radiology the Intersocietal Accreditation Commission and the Joint Commission as the three organizations approved for accrediting facilities. This talk will focus primarily on understanding the ACR requirements and procedures for accreditation of (PET and Nuclear Medicine imaging services) with a focus on the Physicist's role in the process Accreditation by the ACR requires both Acceptance testing and Annual performance testing be performed by a qualified individual. The procedures for performing these tests will be reviewed with a focus on avoiding many of the common pitfalls that may cause facilities to fail the process. The recently modified ACR procedures for acquiring and submitting Quality Control images for review will be discussed.

Other areas that will be covered include the following:

1. Physicist Personnel Qualifications

2. Quality Control Requirements

3. ACR review of clinical and phantom images

Learning Objectives:

1. Understand common pitfalls associated with annual and acceptance testing.

2. Understand the personnel qualifications for physicists.

3. Understand the ACR protocol for acquiring and submission of QC images.

Conflict of Interest: The company that I work for conducts annual performance testing of Nuclear Medicine equipment for facilities in support of ACR accreditation. I am a physics reviewer for the American College of Radiology. I do not speak on behalf American College of Radiology.
TH‐C‐BRA‐02: Image Registration on GPU
Authors: Kim J
Published: August 2010

Medical image registration is a process of aligning two or more sets of images for combining complementary anatomical and functional information. It plays important roles for many radiation therapy applications including tumor delineation target localization for daily treatment adaptive radiation therapy 4D treatment planning etc. However one of the limiting factors for their ways to routine clinical use is their lengthy execution time. It is especially true for intensity‐base deformable image registration (DIR) algorithms. To overcome such problem many researchers have resorted to commodity PC graphics processing units (GPU) which are powerful parallel computation platforms and yet cheap and readily available off the shelves. In the past GPUs had fixed pipeline architectures optimized for rendering graphics primitives such as lines and polygons but modern GPUs are flexible enough for programmers to run general purpose algorithms through special shader or C/C++ like programming languages. Many commonly accepted rigid and non‐rigid registration algorithms have successfully been adapted to GPU architectures. In this session we will review GPU‐based algorithms of 3D/2D registrations that exploit GPU for generating digitally reconstructed radiographs diffusion‐based ones such as Demons and optical flow algorithms mono‐/multi‐modal elastic registration algorithms as well as implementations of mutual information based image registration techniques.

Learning Objectives:

1. To understand basic components of image registration algorithms.

2. To learn the methods of mapping the algorithms to GPU; similarity metrics and transformations.
TH‐C‐BRB‐02: Determination of Average LET of Therapeutic Proton Beams Using A12O3:C Optically Stimulated Luminescence (OSL) Detectors
Authors: Sawakuchi G , Sahoo N , Gasparian P , Rodriguez M , Archambault L , Titt U , Yukihara E
Published: August 2010

Purpose: To measure the linear energy transfer (LET) of therapeutic proton beams using the optically stimulated luminescence (OSL) properties of commercial Al2O3:C dosimeters (OSLDs). Method and Materials: We irradiated Al2O3:C dosimeters at the M. D. Anderson Cancer Center passive scattering nozzles with unmodulated and spread‐out Bragg peak (SOBP) beams. The irradiations with unmodulated beams provided data to determine an LET calibration curve; and the irradiations with SOBP beams tested our LET calibration curve. The OSLDs were readout at Oklahoma State University using a Riso/ TL/OSL‐DA‐15 reader. We normalized our OSL decay curves to their initial intensities and defined the Γ factor as the area under the normalized OSL decay curve which characterized the shape of the OSL decay curve. A validated MCNPX model of the passive scattering beam nozzle was used to determine the average LET of the proton beams. To determine the LET calibration curve OSLDs were irradiated with various beam qualities and the Γ factor was obtained for each irradiation condition. To test the proposed technique we irradiated OSLDs in various depths of clinical SOBP fields. We analyzed the OSLDs and obtained the Γ factor for each irradiation condition and then we used the LET calibration curve to determine the average LET of the fields to which the detectors were irradiated. We calculated the average LET using MCNPX under the same irradiation conditions. Results: Average LET measurements and simulations agreed within 24% and 14% for 140 MeV and 250 MeV SOBP fields respectively. This was the first time that such agreement was obtained using any luminescence detectors (OSLDs and TLDs). Conclusion: The LET dependence of the OSL decay curve's shape from Al2O3:C dosimeters can be used to define an LET calibration curve which in turn can be used to measure average LET of therapeutic proton beams.
TH‐C‐BRB‐04: In Vivo Measurements for Proton Therapy Using a Glass Dosimeter
Authors: Rah J , Shin D , Hwang U , Jeong H , Lee S , Ahn S , Yoon M , Lee S , Park S
Published: August 2010

Purpose: The purpose of this study was to measure the dose distributions near the superficial using a glass dosimeter for proton therapy plans with a varying separation between the target volume and the surface of 3 patients. Method and Materials: All measurements were performed in clinical proton beam at National Cancer Center in Korea. The proton therapy test cases were planned using the Varian Eclipse proton treatment planning system. In vivo surface dosimetry for proton therapy was performed for 3 patients. For all patients the surface doses were measured for delivers using dosimeters (glass dosimeter TLD) placed on the patient's surface. A model GD‐301 glass dosimeter and FGD‐1000 automatic reader were used. In the one case of our patient that GTV was defined from the superficial the surface dose was 189 cGy and the case that GTV was defined by the expansion from the surface by 5 mm it was 138 cGy. Results: The results of glass dosimeter were substantially higher than the TLD result. The doses measured by the glass dosimeter indicated that the proton therapy Eclipse treatment planning system overestimates superficial doses by 7.4±1.9%. The TLD dose test case was 168±2.44 cGy as compared to the calculated dose of 190±4.54 cGy. The calculated and measured doses for the clinical cases where the target volume extends to the surface of the patient indicate that the target will be underdosed without the use of bolus. Conclusion: Given the results of the glass dosimeter and TLD‐100 measurements the calculated doses on the surface of the patient are typically overestimated between 4% and 15%. As such it is recommended that bolus be added for these clinical cases. We also believe that the glass dosimeter has considerable potential to be used for in vivo patient proton dosimetry.
TH‐C‐BRB‐07: Development of a Wall‐Less Fricke Dosimetry System for Megavoltage Photon and Electron Beams
Authors: Cojocaru C , Stucki G , McEwen M , Ross C
Published: August 2010

Purpose: To develop a dosimetry system based on the Fricke (ferrous sulphate) dosimeter that can be used to determine absolute dose in regions of large dose gradients in megavoltage photon and electron beams. Method and Materials: Building on the techniques first used at the Swiss national standards laboratory METAS we have developed a system where Fricke solution can be irradiated in polyethylene bags rather than the usual glass vials. This approach means that there is no wall correction and the dosimeter size and shape can be tailored to each application. As a first test the Fricke system was used to determine the absorbed dose absolutely in low energy electron beams. The Fricke response was compared with the NRC primary standard water calorimeter and calibrated ionization chambers using the TG‐51 protocol. Measurements were made in 4 8 12 18 and 22 MeV beams and the delivered dose was in the range of 7 Gy to 50 Gy. Results: The accuracy and precision of the Fricke dosimetry is very dependent on solution preparation and contaminants which affect the readout. It was found that the contaminating effect of the polyethylene bag on the readout signal was small and could be accurately corrected by using unirradiated controls. The standard uncertainty in the sensitivity coefficient of the Fricke system was found to be 0.2% and the standard uncertainty in the determination of absorbed dose to water was estimated to be 0.6 %. Conclusion: The Fricke dosimeter system remains relevant to megavoltage dosimetry offering accuracy comparable with or better than other integrating systems. The dosimeter is insensitive to dose homogeneities and can be used to determine mean dose to arbitrary volumes. It therefore has applications in reference dosimetry for (TG‐51) non‐compliant beams as well as dose verification in IMRT.
TH‐C‐BRB‐08: Improving Reference Dosimetry of Nonstandard Beams
Authors: Bouchard H , Kawrakow I , Carrier J , Lacroix F , Chung E , Seuntjens J
Published: August 2010

Purpose: First to characterize the factors responsible for non‐unity corrections in nonstandard beam dosimetry and provide conceptual solutions to minimize corrections. Second to provide methods to estimate uncertainties accurately in nonstandard beam dosimetry and achievable levels in clinical situations. Materials: Ionization chamber response to static and dynamic IMRT deliveries is simulated using Monte Carlo and chamber perturbation factors are calculated. An exhaustive characterization and uncertainty analysis method applied to radiochromic film dosimetry is performed. Experimental criteria for achieving required levels of uncertainties are predicted using the method. An implementation of a Monte Carlo based setup positioning‐induced dose uncertainty (PIDU) is performed in egs_chamber to evaluate uncertainties during ionization chamber measurements. An Exradin A12 chamber and a PTW 60012 diode models are used to numerically evaluate PIDU in nonstandard beams. Results: Results show that the factor responsible for large corrections factors in nonstandard beams is the gradient effect. Reporting dose to the sensitive volume of the chamber filled with water reduces the correction factor by half under high gradients. A theoretical expression of correction factors is obtained for ideal nonstandard reference fields. Levels of uncertainty of the order of 0.3% are achieved with strict procedures of radiochromic film dosimetry and show great potential for non‐standard beam measurements. Realistic uncertainties up to 4% on IMRT kQ factor measurements are reported using the Exradin A12 in modulated fields. Realistic uncertainties up to 3% using a PTW 60012 diode are reported for small beam output factor measurements. Conclusions: Reporting dose to the volume of the chamber instead of a point of measurement could reduce the correction factors. Depending on outcomes of future developments corrections could be eliminated. Uncertainties in non‐standard beams are an important issue during QA routine and reference dosimetry and could be a limiting factor in the new protocol generation.
TH‐C‐204B‐01: Dosimetrical Characterization of an X‐Ray Microbeam‐Grid Based Therapy (MRT) for Treatments of Deep‐Seated Lesions
Authors: Siegbahn EA , Anderson D , Warkentin B
Published: August 2010

Purpose: Spatially‐fractionated X‐ray microbeam‐grid therapy (MRT) is being developed at a few synchrotron laboratories around the world. To evaluate this new technique small experimental animals e.g. rodents some bearing a transplanted tumour have been treated. Preclinical trials ultimately aimed at treating humans are now moving forward with the intermediate goal of treating larger animals e.g. rabbits cats dogs and monkeys. Here we compare the dose distributions obtained from Monte Carlo simulations of irradiations of phantoms representing small and large animal heads. Method and Materials: The microbeams used for MRT are linearly‐polarized extremely intense and of relatively low‐energy (100's of keV). We used the PENELOPE Monte Carlo code which is particularly suitable for this application because it implements accurate low‐energy X‐ray and electron cross sections and allows incorporation of the beam polarization. Results: The dose enhancement in the skull bone on the entrance and exit sides was determined. The variation of the peak and valley doses (doses inside and in between the microbeams) with depth was found to depend on the size of the microbeam array used an increase in array size leads to a shift in the dose profiles towards larger depths. The salient finding of this study is that for larger microbeam arrays necessary for treating larger animals valley doses are increased by more than 100% while the peak doses were considerably less affected. Conclusion: This work shows the relationships between the absolute microbeam array dimensions and the doses to targeted lesions and normal tissues at various depths in large and small animals — both in the paths of the microbeams and in between them. The results predict that the doses between the microbeams within the irradiated targets are significantly increased in larger animals compared to smaller ones suggesting a potentially increased therapeutic effect for the larger animals.
TH‐C‐204B‐02: Monte Carlo Feasibility Study of a Compact Microbeam Small Animal Irradiator
Authors: Schreiber E , Chang S
Published: August 2010

Purpose: Microbeam radiation therapy (MRT) is a promising but poorly understood experimental treatment modality. As an alternative to synchrotron‐based facilities we propose a compact carbon nanotube‐based MRT device for small animal research. We report on a Monte Carlo‐based feasibility study of the proposed design. Method and Materials: Monte Carlo calculations were performed using EGSnrc‐based codes. The proposed device design includes a carbon nanotube cathode shaped to match the collimator aperture a reflection anode with filter and a microbeam collimator. The collimator is sized to deliver a beam width ranging from 30–200 microns at 15 cm SAD. Design parameters studied with Monte Carlo include electron energy anode angle filtration and collimator design. Results: Increasing the energy from 100 kVp to 150 kVp increased the photon fluence through the collimator by a factor of 1.7. Both energies produced a largely uniform fluence along the microbeam with 5% decreases in intensity near the edges of the long dimension. The isocentric dose rate for 150 kVp was calculated to be 1200 Gy/min/A in the center of a 3 cm diameter target. Expected cathode currents of 1 A project an isocentric dose rate of 80 Gy/sec for a four‐beam system. Scatter contributions resulting from collimator size were found to produce only small (<7%) changes in the dose rate for field widths greater than 50 microns. Dose vs. depth was weakly dependant on filtration material. The peak‐to‐valley ratio outside the beam was less than 0.5% indicating the valley dose between adjacent microbeams will be no more than 1% of the peak dose. Conclusion: Monte Carlo simulations demonstrate that the proposed microbeam device will be capable of delivering a sufficient dose rate and peak‐to‐valley‐ratio to be useful for small‐animal MRT studies.

Conflict of interest: The work is supported by NIH grant 1RC2CA148487‐01
TH‐C‐204C‐03: Radiation Necrosis and Its Characterization Using Advanced MRI
Authors: Jost S , Garbow J
Published: August 2010

Patients with malignant brain tumors are typically treated with a combination of surgery chemotherapy and radiotherapy. As no combination of treatments has yet proven curative the majority of patients eventually experience a recurrence of their tumor. Significant subsets of patients develop MR imaging findings following these therapies that can be difficult to interpret. Radiation necrosis is the most common and most significant of these treatment‐associated changes as its anatomic imaging characteristics are remarkably similar to those of recurrent tumor. The development of non‐invasive imaging markers of diagnostic specificity is an important goal for clinicians caring for patients with brain tumors. Recent advances in imaging specifically exploiting PET imaging tracers that measure cell proliferation and advanced MR imaging techniques including perfusion and diffusion‐weighted imaging as well as Magnetic Resonance Spectroscopy afford unique opportunities to monitor tumor biology in vivo. Despite these advances no single imaging modality with sufficient diagnostic sensitivity and specificity to identify radiation necrosis versus tumor recurrence has been identified. Until recently few small‐animal models of radiation necrosis in brain tissue have been reported. Previous models were developed primarily in rats and employed only a small number of radiation fractions. Recent models have evolved to describe the development of a radiation necrosis model in mice that employ focal multi‐fraction radiation to more accurately reflect the clinical situation encountered by patients treated for malignant brain tumors. The recent development of a conformal pre‐clinical irradiation system has demonstrated that high dose focal fractionated brain irradiation in small animals is feasible and can generate relevant pre‐clinical models of radiation necrosis. In addition modification of the clinical gamma‐knife irradiation system used in humans for stereotactic radiosurgery has also been used to develop a murine model for radiation necrosis.

The lecture will discuss the clinical importance of diagnosing radiation necrosis and distinguishing it from growing tumor and will also address ongoing basic science research considering these questions of diagnostic specificity in two small animal models of radiation necrosis. In addition the lecture will address translational clinical work considering advanced imaging applications for this clinical problem in human patients with malignant brain tumors.

Learning Objectives:

1. Understand the clinical problem of radiation necrosis in patients with neuro‐oncology.

2. Understand the relevance of advanced MR imaging methods in diagnosing radiation necrosis in patients with malignant brain tumors.

3. Understand the murine models for radiation necrosis and their suitability for basic and translational research focusing on this clinical problems.
TH‐D‐BRA‐04: Late Effects from Diagnostic Imaging
Authors: Kaste S
Published: August 2010

Over the past several decades the use of medical imaging has progressively increased to the point where it accounts for the greatest exposure of ionizing radiation to the general population. The use of CT alone has grown to over 60 million studies per year in the United States and represents the largest contribution to medical radiation exposure. Of these about 11% (>7 million) are performed on pediatric patients.

Pediatric patients are particularly susceptible to the effects of radiation exposure as their tissues are two to ten‐times more susceptible to adverse effects associated with such exposure compared to adults. Further children have a lifetime in which to manifest radiation‐induced effects such a cataracts and the development of cancer. As radiation exposure is cumulative each exposure must be considered in deciding whether or not the benefit of performing the study outweighs its risk.

Limiting patient exposure from medical imaging is multifactorial and requires judicious use of indicated studies performed with appropriate techniques on equipment that optimizes information while minimizing radiation exposure. Education is key to optimizing medical imaging while minimizing patient risk. Included in such initiatives is public education regarding appropriate use and potential risk of excessive use education of technologists radiologists and healthcare providers in general and technical improvements of imaging modalities.

This presentation will provide an overview to issues specific to pediatric imaging where minimizing exposure to ionizing radiation is critically important and address potential long‐term effects of such exposure.

Learning Objectives:

1. Understand that pediatric patients are not just small adults.

2. Learn methods for controlling exposure to ionizing radiation in medical imaging.

3. Learn potential sequelae of exposure to ionizing radiation in pediatrics.
TH‐D‐201C‐04: Quantification of Cellular Response in Myocardial Infarction Using Iron Oxide Particles‐Enhanced MRI
Authors: Yang Y , Liu J , Yang Y , Shi X , Hill W , Hu T
Published: August 2010

Purpose: To quantify the cellular response in myocardial infarction by using iron oxide particles cell labeling and MR imaging techniques. Method and Materials: Iron oxide particles can produce signal attenuation in MRI and were used to label either macrophages or mesenchymal stem cells. Macrophages were labeled via an intravenous administration of iron oxide particles whereas mesenchymal stem cells were labeled in vitro and then transplanted into the animal bone marrow. In the macrophage study varied doses (1.1–14.5 μg Fe/g body weight) were applied. After surgically inducing a myocardial infarction in the C57 mouse the labeled cells would mobilize to the infarction site attempting to repair the damaged tissue. To monitor the cellular response T2*‐weighted MRI was used to acquire short‐axis cardiac images at 3 7 14 and 21 days post‐infarction. Signal intensity normalized to the maximum signal from the ventricular blood was used to quantify labeled cells at infarction sites. Results: Cellular response during myocardial infarction was temporally and noninvasively monitored. In the macrophage study linear regression of normalized signal intensity at each time point revealed a linear relationship between the normalized signal intensity and iron oxide dose at 7 days (r2=0.92) and 14 days (r2=0.98) post‐infarction. An optimum dose as well as imaging time window for monitoring inflammatory cell response was also obtained. Either labeled macrophages or mesenchymal stem cells were evidenced at the infarction site in histology. Conclusions: A linear signal‐dose relationship at 7 and 14 days post‐infarction suggests that the number of labeled cells at the infarction site can be interpreted from the MR signal within this time window. This linear relationship may further apply to quantify labeled mesenchymal stem cells. Therefore the cell labeling and MR imaging technique have a potential to quantify cellular response in pathological processes as well as during cell therapy.
TH‐D‐201C‐06: Preliminary Performance of a DTI Capillary Phantom in a Quality Assurance Experiment
Authors: Woodbury G , Yanasak N
Published: August 2010

Purpose: The purpose of this study was to determine the measurement stability of fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) using a phantom in conjunction with a diffusion tensor imaging (DTI) sequence. Given an appropriate phantom with anisotropic structures procedures could be developed for DTI for monitoring daily quality assurance. Methods and Materials: A doped water‐filled phantom was constructed containing four separate arrays of glass capillaries of varying diameter. A cork phantom holder was constructed for proper and reproducible placement of the phantom within the GE Excite HDx 3.0T MRI scanner. MRI images of the phantom were acquired in fourteen separate scan sessions. To evaluate intra‐session reproducibility of mechanical phantom alignment and slice prescription reproducibility software was used to coregister images from each session and determine displacement. Temperature and signal‐to‐noise measurements of the phantom were made for each scan session. Data acquired from the scan sessions were used to calculate FA and ADC which were evaluated for dependency with respect to phantom temperature and SNR. Results: Mean absolute displacements in alignment were 3.45mm along the S‐I axis 0.74mm along the A‐P axis and 1.70mm along the R‐L axis. Slice prescription was determined to vary by approximately 14.3% of DTI slice volume from session to session. FA and ADC were not significantly dependent on SNR (p>0.45) but were significantly dependent on temperature (p<0.003). After temperature corrections FA and ADC were stable temporally to within <6% and <2% respectively. Conclusion: Using our anisotropic diffusion phantom we determined that daily FA and ADC variations correlate significantly with temperature but not on SNR. After correcting these biases residual FA and ADC are stable to within a few percent.
TH‐D‐201C‐09: Evaluation of Metabolomics Data Using Univariate and Multivariate Statistical Analysis Techniques
Authors: Moroz J , Fallone G , Syme A , Allalunis‐Turner J
Published: August 2010

Purpose: To quantify urinary metabolic changes in experimental animals as they transitioned from healthy to tumor bearing. Univariate and multivariate statistical tests were used to identify patterns of metabolic behaviour that changed in a significant manner. Receiver operator characteristic (ROC) curve analysis was used to evaluate the utility of the tests. Method and Materials: Human GBM cells were grown as xenografts in NIH iii nude mice at 6 weeks of age. Urine samples were collected daily beginning one week prior to cell injections and lasting four weeks after injection. Selected samples were run on an Oxford 800MHz cold probe NMR Spectrometer (Oxford England) utilizing a 1‐D NOESY pulse sequence. The acquired spectra were analyzed by targeted profiling using Chenomx Suite 5.1 (Chenomx Inc Edmonton Canada). The paired t‐test was used to evaluate changes in metabolite concentrations in the pre‐injection population compared to the post‐injection population. The same test was also applied to metabolite ratios. Principal component analysis (PCA) and partial least squares discriminant analysis (PDS‐DA) were used to search for more complicated relationships in the data. Results: Application of the t‐test to the ratios of metabolites revealed 20 ratios that were significant beyond the Bonferroni correction threshold and 152 more ratios were significant under the FDR condition. Of the significant ratios 7 had an AUC greater than 0.9 and 68 had an AUC between 0.8 and 0.9. After correcting for changes found in the control animals 12 and 36 ratios that satisfied the Bonferroni and FDR thresholds respectively. 6 ratios had an AUC exceeding 0.9 and a further 16 having an AUC greater than 0.8. Conclusion: Metabolic profiling of urine samples in animal models demonstrates that this technique has the potential to serve as a screening tool for certain types of cancers.
TH‐D‐201C‐10: Improved Quantification of the CH2/CH3 Ratio of Lipids: Illustration in Vivo on Tibial Bone Marrow at 3 T
Authors: Yahya A. , Fallone B.G.
Published: August 2010

Purpose: To improve the accuracy of lipid CH2/CH3 ratios determined by proton magnetic resonance spectroscopy (MRS) by minimizing J‐coupling modulations of the CH3 lipid peak. Method and Materials: Experiments were conducted in vivo on the tibial bone marrow lipids of four volunteers at 3 T. A regular PRESS (Point RESolved Spectroscopy) sequence was used to estimate the T2 (transverse relaxation) of the CH2 protons by acquiring spectra at five echo times (TEs) and plotting the areas as a function of TE. The curve was fitted to the function Moexp(−TE/T2) where M0 is proportional to the CH2 proton concentration. The CH3 response to a regular PRESS sequence is modulated due to J‐coupling interactions and does not decay monotonically. To determine Mo of the CH3 protons a narrow‐bandwidth PRESS sequence was designed that rewinds the J‐coupling evolution of the CH3 protons in the voxel of interest and spectra were acquired with the same five TEs. The CH2/CH3 ratio was calculated by dividing the CH2 Mo by that determined for CH3 and the result was multiplied by 1.5 to compensate for the different proton multiplicities. Results: The mean T2 of the CH2 protons was estimated to be ≈ 88 ms. Applying the narrow‐bandwidth PRESS sequence minimized CH3 signal variations due to J‐coupling and resulted in a decay curve that could be described by a monoexponential T2 decay function. The mean T2 for the CH3 protons was ≈ 133 ms. A mean ratio of 12:1 was calculated for the CH2:CH3 ratio of the tibial bone marrow lipids of all volunteers. Conclusion: The presented PRESS sequence enables the T2 of the CH3 lipid protons to be measured with more accuracy than would be determined by using short‐TEs thereby allowing a more accurate measure of the CH2/CH3 lipid composition ratio to be determined.
Sci—Thur PM: YIS — 07: A Two Dimensional Plastic Scintillation Detector Array for Quality Assurance of Intensity Modulated Radiation Therapy
Authors: Guillot M , Gingras L , Archambault L , Beddar S , Beaulieu L
Published: August 2010

Purpose: The goals of this study are: 1) to present a novel two Dimensional Plastic Scintillation Detector array (2D‐PSD) for measurements of complex dose distributions, 2) to demonstrate that the 2D‐PSD can be used for high accuracy dose measurements for variable beam incidences. Methods and Materials: The 2D‐PSD consists of 781 PSDs inserted vertically in a plastic water slab covering a 26×26 cm2 region. The prototype is built entirely from nearly water equivalent plastic materials. To characterize the angular dependence of the 2D‐PSD, the detector array was irradiated with a square field size 10×10 cm2 using variable beam incidences from 0° to 120°. Furthermore, a clinical head and neck IMRT plan composed of nine beams was delivered on the 2D‐PSD by keeping the gantry of the linear accelerator fixed at 0°. The dose distributions measured with the 2D‐PSD were compared to calculations from a treatment planning system (Pinnacle3, Philips Medical Systems) on a CT scan of the 2D‐PSD and with measurements taken with an ionization chambers array (MatriXX Evolution, IBA Dosimetry). Results: The results from the angular dependence study indicate an excellent agreement between the measured and calculated dose distributions. The gamma evaluation of the IMRT plan delivered was successful for 98.5% of the detectors for a dose tolerance of 3% and a distance to agreement of 3 mm. Conclusion: The results presented in this work suggest that the developed 2D‐PSD could be used as a quality assurance tool for IMRT and arc therapy patient plan verification.
Sci—Thur PM: YIS — 08: Comparison of New In‐Vivo Measurements for Dosimetry of Rb‐82 with Prior Blood Flow Model Predictions
Authors: Hunter C , Ziadi C , Etele J , Hill J , Beanlands R , deKemp R
Published: August 2010

Published radiation dose estimates for Rubidium‐82 include two In‐Vivo studies and two theoretical blood flow models, the results of which vary widely. Rb‐82 internal organ and effective doses with PET/CT in humans were determined and compared to the published estimates with emphasis given to the differences between in‐vivo measurements and blood flow model predictions. 26 cardiac patients and 4 normal subjects with no cardiac history were recruited. Dynamic 3D PET scans were acquired (GE Discovery RX/VCT) over 10 minutes following IV injection of 10 MBq/kg Rb‐82. Images were reconstructed using FORE‐OSEM and 8 mm Hann filter. Cardiac scans of the chest were acquired at rest for all 30 subjects, plus one additional scan of the Head, Neck, Abdomen, Pelvis, or Thighs. Mean Rb‐82 residence times were determined in 22 source organs using volumes‐of‐interest drawn on the fused PET/CT images. At least 4 samples were obtained in each source organ. Using ICRP 103, the male and female effective doses were 0.00074 and 0.00092 mSv/MBq respectively. The lungs were found to be the major contributors to the effective dose for all in‐vivo studies, whereas it was the thyroid for both blood flow models. These dose estimates for Rubidium‐82 are the first to be measured directly with PET/CT in humans, and are in agreement with the two in‐vivo measurements but 2 to 3 times lower than blood flow models. The new values derived from human studies suggest a typical effective dose of 0.6 mSv per scan with 3D PET.
Sci—Thur PM: YIS — 10: Magnetically Shielding the Linac in a Bi‐Planar Linac‐MR System
Authors: Aubin J St. , Steciw S , Fallone BG
Published: August 2010

Purpose: A low field bi‐planar linac‐MR system has been proposed to achieve real‐time image guided radiotherapy. The close proximity of the linac to the MR imager necessitates magnetic shielding to reduce the transverse magnetic fringe field magnitude. Method: Optimized magnetic shielding was designed based on simulations of linac performance in transverse magnetic fields. The linac simulation consisted of an electron gun (EGN2w, COMSOL, PARMELA), and a linac waveguide (COMSOL). The radio‐frequency field within the waveguide was calculated using COMSOL. The linac simulation generated an electron phase space at the linac target which was inputted into BEAMnrc and DOSXYZnrc to simulate dose distributions. Validation of the linac simulation was performed against measurements from a Varian 600C. Passive magnetic shielding was designed in COMSOL and active shielding was designed in the form of four current carrying coil pairs surrounding the linac. Results: The linac simulation at 0 G provided excellent agreement to all electrical and dosimetric measurements. The dosimetric effects of profile asymmetry or lateral shift caused by transverse magnetic fields on the linac were corrected through a shifting of the electron focal spot (as done in linac commissioning) and through asymmetric jaw positions. With no net dosimetric effects caused by transverse magnetic fields, linac performance was only limited by beam losses which increased with magnetic field strength. Passive and active shielding was optimized meeting all design constraints. Conclusion: Magnetic decoupling of the linac in a low field bi‐planar linac‐MR system has been accomplished using either passive or active shielding.
Poster — Thur Eve — 07: Measurement of Radiation‐Light Congruence Using a Photodiode Array
Authors: Balderson M , Spencer DP , Nygren I , Brown D
Published: August 2010

Many factors affect treatment delivery, including setup errors during the simulation process, dose calculation uncertainty, patient setup errors during treatment, and errors that result from incorrect calibration and geometric setup of the linear accelerator. Among these, the radiation‐light congruence is especially important because the light field is used to simulate the radiation beam. The light field is an integral part of patient setup and jaw calibration, thus radiation‐light congruence is essential for accurate treatment delivery. We have developed a novel device that enables precise and automated measurement of radiation‐light congruence. Using the device, we show that the radiation‐light field congruence for both 6 and 15 MV beams is within standard tolerance limits. However, our results indicate that radiation‐light congruence is dependent on collimator angle and energy. The maximum measured disagreement between radiation field edge and light field edge was 1.290 ± 0.004 mm at collimator angle 270 (X1, 15 MV) and 0.932 ± 0.003 mm at collimator angle 90 (Y2, 15MV). The minimum disagreement was 0.016 ± 0.003 mm for 270 (X2, 6 MV) and 0.102 ± 0.004 mm for 90 (X2, 6MV). This detector and measurement method will give us a better understanding of the radiation‐light congruence dependence on collimator angle and energy. It could also be used to determine location of the x‐ray source within the linear accelerator.
Poster — Thur Eve — 10: User Dependence of Three Radiation Oncology Incident Reporting Ranking Systems
Authors: Carlone M , Daniels B , Goharian M , Lau H , MacPherson M , Dunscombe P
Published: August 2010

The recent public scrutiny of errors in radiation therapy has underscored the need for incident reporting and classification mechanisms in the field. Several such systems have been proposed by various national and international organizations. The utility of any incident classification scheme ultimately will depend on how uniformly the system can be used and interpreted. Here we present a systematic assessment of these incident classification systems. Three different incident classification schemes were used in this evaluation. The Autorite de Surete Nucleaire together with the Socitete Fracaise de Radiotherapie Oncologique (ASN‐SFRO)); the British Institute of Radiology (BIR); the American Association of Physicists in Medicine Task Group 100 (TG100). We have applied these severity rankings to incidents taken from a compendium of errors published by the World Health Organization (WHO). This compendium provided the details for twenty radiotherapy incidents and twenty‐eight “near‐misses”. Six individuals were asked to rank each of these incidents using each of the three classification schemes. Study participants included four physicists and two radiation oncologist. The Friedman test was applied to test the null hypothesis that the rankings are consistently applied by all observers. The results suggest that the six rankers did not apply the ranking method consistently. This suggests that more quantitative methods are needed to score radiotherapy incidents such that better consistency can be achieved in incident reporting.
Poster — Thur Eve — 18: Differential Dose‐Volume Histogram Modeling Using the Gaussian Error Function
Authors: Chow J , Markel D , Jiang R
Published: August 2010

The Gaussian error function (GEF) was first used to model rectal differential dose‐volume histograms (dDVH) for prostate intensity modulated radiation therapy (IMRT) plans incorporated with the interfraction prostate motion. Seven‐beam IMRT treatment plans were created in three patients with small (40 cm3), medium (53 cm3) and large (87 cm3) prostate volume, selected from a group of 20 patients. The interfraction prostate motions were measured by comparing the digitally‐reconstructed radiographs (anterior and lateral views) from the original treatment plans to the corresponding daily electronic portal images in the treatment unit based on the implanted fiducial gold markers. The ranges of prostate motion were found to be 8 – 2 mm, 4 – 8 mm and 4 – 3 mm along the anterior‐posterior directions for the small, medium and large prostate patient, respectively. Rectal dDVH varying with the interfraction prostate motion were determined by the treatment planning system (TPS), and modeled by the GEF for the three patients. It was found that the rectal dDVH from the prostate plans modeled by the GEF agreed well with those calculated by the TPS. The successful modeling of dDVH results in a significant reduction of the dDVH database, because typically about 12 parameters of the GEF model can be used to substitute about 800 – 1000 dose‐volume bin set for each dDVH. This can greatly reduce the computer memory in the normal tissue complication probability calculation associated with a huge dDVH database.
Poster — Thur Eve — 19: Polyvinyl Alcohol Cryogels: A Promising Material for Tissue‐Mimicking Optical Phantoms
Authors: Counter G , Campbell G , Diamond K
Published: August 2010

Tissue‐mimicking phantoms with specific radiological, elastic, or optical properties are desirable for calibration and quality assurance purposes. Polyvinyl alcohol (PVA) is a non‐toxic, water‐soluble polymer with many existing uses in medicine, ranging from artificial tissues for use in humans to anatomical phantoms for magnetic resonance imaging and ultrasound. It has not been well characterized optically. The process by which the polymer is crosslinked, repeated freeze‐thaw cycles, imparts optical properties that lie in the range of tissue and can be selectively tuned using different production conditions. A double integrating sphere system has been constructed to measure diffuse reflectance and transmittance from an illuminated sample. Monte Carlo modeling of the measurement geometry allows for optical property estimation using the Marquardt‐Levenberg algorithm. The scattering by PVA cryogels increases with additional freeze‐thaw cycles. PVA scattering is also affected by the ambient conditions at the time of production. Most tissue scattering properties can be mimicked using 6 freeze‐thaw cycles at most.
Poster — Thur Eve — 26: Cinical Implimentation of kV CBCT for Gynecological IMRT
Authors: Qiu Y , Bachand F , Moiseenko V , Lim P , Aquino‐Parsons C , Duzenli C
Published: August 2010

The aim of this work was to implement CBCT imaging for assessment of CTV coverage for IMRT treatment of gynecological malignancies. A cone beam CT imaging protocol was developed to assist with assessment of organ motion and dose volume analysis. Accurate assessment of CBCT dosimetry using Monte Carlo simulations was performed to allow selection of a CBCT imaging protocol that was deemed to not elevate the risk of second malignancy as well as providing the opportunity to incorporate CBCT doses into the treatment plan. Assessment of CTV coverage was performed by contouring structures on multiple CBCT images for each patient. Dose volume calculations were performed on the CBCT data sets for the CTV segmented into vessel and vaginal regions, bladder and rectum. Measurements of bladder and rectal volumes, intra‐organ distance and marker seed positions are reported. Data was collected for patients treated between fall 2009 and spring 2010 using a seven field sliding window IMRT technique. It is concluded that routine CBCT imaging provides a safe and effective method of assessing the impact of organ motion for patients under going gynae IMRT. The posterior‐superior margin of the vaginal CTV may be impacted by bladder and rectal filling which should be accounted either through appropriate patient preparation protocols or by PTV margin adjustment. The feasibility of using fiducial markers for daily assessment of CTV coverage is the subject of ongoing investigation.
Poster — Thur Eve — 32: Radiation Dose from a Proposed Measurement of Arsenic and Selenium in Human Skin
Authors: Gherase MR , Mader JE , Fleming DEB
Published: August 2010

Dose measurements following 10 minute irradiations with a portable x‐ray fluorescence (XRF) spectrometer composed of a miniature x‐ray tube and a silicon PiN diode detector were performed using thermoluminescent dosimeters consisting of LiF:Mg,Ti chips of 3 mm diameter and 0.4 mm thickness. The table‐top setup of the XRF spectrometer was used for all measurements. The setup included a stainless steel lid which served as a radiation shield. Two rectangular polyethylene skin/soft tissue phantoms with two cylindrical plaster of Paris bone phantoms (diameters of 5 and 10 mm) were used to study the effect of x‐ray beam attenuation and backscatter on the measured dose. Eight different irradiation experiments were performed. The average dose rate values measured with TLD chips within a 1×1 cm2 area were between 4.8 and 12.8 mGy min−1. The average dose rate values of the irradiations with 10 mm diameter bone phantom were higher than the corresponding values with the 5 mm diameter bone phantom. This demonstrated that the dose contribution of the bone backscattered radiation cannot be neglected. The dose measurements demonstrated that no significant health risks can be expected from a two minute irradiation of a commercial XRF spectrometer. The corresponding skin equivalent dose for a two minute irradiation was calculated to be 13.2 mSv. This value is lower than the ICRP Report 60 (1991) annual dose limit for the general population of 50 mSv for a 1×1 cm2 skin area.
Poster — Thur Eve — 34: Accelerated Analytical Scatter Estimation with Graphics Processing Units
Authors: Ingleby H , Lippuner J , Elbakri I , Rickey D
Published: August 2010

Image degradation due to scatter can be a serious problem in x‐ray imaging, particularly in cone‐beam computed tomography because of the high scatter to primary ratio. Computational methods to estimate scatter are useful both for system modeling and optimization as well as algorithmic scatter correction. Computational scatter estimators are generally based on either Monte Carlo simulation or analytical calculations. Monte Carlo methods can incorporate very accurate models of interaction physics, but are typically very time consuming. Analytical methods, while usually less accurate than Monte Carlo due to simplifications required to render them computationally tractable, are more amenable to acceleration by parallelization. We previously developed an analytical method for estimating Compton and Rayleigh single scatter for a voxelized phantom in a cone beam geometry. Scatter estimates produced with our initial Matlab code showed good agreement with those obtained from Monte Carlo simulation of an identical imaging geometry in EGSnrc. Computation time with the analytical code was still significant, however, especially when using a high‐resolution phantom with small voxels. Our goal for this project was to accelerate our analytical scatter estimator, without loss of accuracy, by porting the code for use with Nvidia graphics processing units (GPUs) with the CUDA programming environment. Using four GPUs, we obtained speed‐up factors of approximately 700X relative to the original Matlab code running on a single CPU while maintaining good agreement with our reference Monte Carlo results. We plan to apply our GPU‐based analytical scatter estimator to a scatter correction algorithm for cone beam computed tomography.