bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐C‐204B‐07: Development of Image‐Guided Radiosurgery with Novalis TX for Small Animal Study
Authors: Yan H , Koontz B , Kimura M , Vujaskovic Z , Yin F
Published: August 2010

Purpose: Developing a protocol to accomplish small animal radiosurgery study conducted at our clinic in evaluating radiation‐induced erectile dysfunction. Method and Materials: Animals were sedated and scanned using commercial CT scanner. Scans were imported into clinical treatment planning system. All interested anatomic structures were contoured. Two dynamic arc plans (using conformal arc and RapidArc techniques) were created for all animals. On‐line target localization was conducted using 2D on‐board imaging (OBI) and 3D cone‐beam CT (CBCT). The treatment plans were finally delivered to animal on Novalis TX. Quality assurance (QA) for the delivered plans was conducted to evaluate delivery accuracy. Results: The mean conformity index (100% dose cloud/PTV volume) for all plans was 1.6 showing minimal inclusion of non‐target structures within the high‐dose region. Median rectal dose for conformal arc plans was 41.6% of prescription for RapidArc 19% of prescription. The mean shifts are −0.3 cm ±0.5 cm 2.0 cm ±0.3 cm and 0.2 cm ±0.1 cm in three dimensions based on 2D OBI matching and less than 0.1 cm based on 3D CBCT registration. Dose difference of QA plans are 2.6% and 1.6% for confromal and RapidArc plan at measured points (treatment isocenter) while the gamma indexes of pixels within range [0 1] are 98.4% and 97.3% for conformal and RapidArc plan Based on 2D dose measurement. Conclusion: The conformal arc plans were more homogeneous in treatment delivery and were well tolerated by the animals. The 2D on‐line target localization for small animal is feasible and efficient. All QA plans passed the acceptance criteria which is used in our clinic and demonstrated a strong agreement between doses of delivered plans and calculated plans. Tightly dynamic arc plans to treat small animal prostate with minimal injury of non‐target structures is feasible using Novalis TX and OBI.
TH‐C‐204B‐09: Development of a Small Animal Imaging and Therapy System: An Open Source Medical Devices (OSMD) Concept
Authors: Prajapati S , Mackie T , Jeraj R
Published: August 2010

Purpose: The open source medical devices (OSMD) concept aims to facilitate and promote medical research as an open source technology. The goal is to collaborate among research groups and companies to develop medical technologies that are affordable and available to research groups around the world especially in those places with limited research resources. We propose implementing the OSMD concept to develop a small animal combined PET/CT/RT system. Method and Materials: The first phase of the project was to define the technical specifications for a preliminary design of a small animal hybrid PET/CT/RT system. Next we will collaborate with international research communities to explore potential designs and finalize hardware software and management of the design. Lastly we will build the working system and perform necessary checks before open sourcing the technology. Results: This pioneer PET/CT/RT system is designed with modular systems utilizing both anatomical and functional imaging to guide the intensity modulated radiotherapy. We are developing a computer‐aided model of the preliminary design with tentative technical specifications of various components of the system. We are especially vigilant in developing software and management systems up to clinical standards so that they can be directly translated for human use. Conclusion: The OSMD concept has been initiated. We are planning to host the OSMD Conference in fall 2010 to launch the global proposal of OSMD mainly focusing on the development of a small animal hybrid PET/CT/RT system. Interested individuals and groups can contribute to finalize the hardware and software design of this multimodality system. Everybody can be benefited from this technology as a freely accessible technology. OSMD projects can promote medical research by facilitating medical instruments to the places with limited research resources.
TH‐C‐204B‐10: Implementation of a Small Animal Image Guided Microirradiator: The MicroIGRT
Authors: Izaguirre E. W. , Chen H , Su I , Silvius A. A. , Birch J , Price S.G. , Low D. A.
Published: August 2010

Purpose: Implementation of a conformal small animal image guided microirradiation therapy instrument (microIGRT) consisting of a cone beam microCT subsystem for submillimeter low dose structural imaging image guided radiotherapy and orthovoltage conformal microirradiation with high dose rate and high throughput. Method and Materials: The microCT subsystem is based on an 80kVp micro‐focus x‐ray source with 75×75 μm2 focal spot and a flat panel amorphous silicon detector with 1024×1024 pixels. The irradiator consists of a high power commercially available 320 kVp orthovoltage source with a 0.4×0.4 mm2 focal spot that can be operated at a nominal power of 800W. The beam characteristics are controlled with two variable jaws used to pre‐collimate the radiation beam along each orthogonal direction. An aperture exchange mechanism is used to conform the beam cross section by using computer generated apertures. The microCT radiation dose the orthovoltage source spectral output and dose rate are under evaluation using a mouse digital phantom and a pencil beam algorithm. Results: CT imaging with micrometric resolution is achievable using 128 projections and a maximum radiation dose of 2cGy. Automatic animal positioning and handling is performed within sub‐millimeter precision. The treatment beam can be aimed at different latitude and longitude angles and translated with 500 μm steps. The source was tested to deliver a radiation dose rate of 20 Gy/min when is filtered to a half‐value layer of 4.6 mm Cu. Conclusion: We present our progress and initial tests of a highly conformal image guided small animal microirradiator.
TH‐D‐BRA‐01: Epidemiologic Evidence of Late Effects from Diagnostic Imaging and Radiation Therapy
Authors: Howell R
Published: August 2010

Owing to advances in diagnostic imaging chemotherapy and radiation therapy (RT) the survival rate for many types of cancer has greatly improved in recent years. Considering this increased survival rate many of these patients will face late complications in the years following treatment. In particular long‐term survivors are at a substantially increased risk for radiation related late effects such as second cancers and cardiovascular disease. Research in late effects includes population based epidemiological studies that quantify the relationship between excess risk and radiation dose. An additional aspect of late effects research aims to reduce dose to radiosensitive organs and tissues associated with excess risk for late effects while maintaining equivalent or improved local control. The quantification of radiation‐induced late effects and the use of modern delivery techniques to reduce such effects is an important and growing area of research in medical physics as evidenced by a recent surge in publications.

The objective of this symposium is to provide an overview of related late effects following diagnostic imaging and radiation therapy. Within the context of the symposium objectives the first presentation in the session will provide context for the symposium by providing an overview of National Cancer Institute and European Cancer Registries epidemiological studies for radiation related second cancers cardiovascular disease and other late effects. Specifically the presentation will focus on epidemiological data and dose response relationships for second cancers and will discuss the need for additional studies to better establish dose response relationships for cardiovascular disease for various cardiac toxicity endpoints.

Learning Objectives:

1. Understand sources of epidemiological data for radiation related late effects.

2. Understand limitations of epidemiological data for radiation related late effects.

3. Understand dose response relationships for specific late effects.
TH‐D‐BRA‐02: Late Effects from Modern Radiation Therapy
Authors: Newhauser W
Published: August 2010

Long‐term survival rates for patients with cancer are large and increasing. In survivors who received radiotherapy the prevalence of radiogenic late effects is also large and increasing with the potential to become a public health issue of considerable proportion. A multitude of late effects are associated with radiation exposure include the development of second cancers cardiac toxicity cognitive deficits and musculoskeletal growth abnormalities in children. In modern radiotherapy much effort is devoted to developing personalized treatments that control the tumor while minimizing acute toxicities to surrounding healthy tissues; comparatively less attention is paid to minimizing late effects. However in recent years much progress has been made toward quantifying the radiation exposures and the associated risks of late effects from modern external beam radiation radiotherapies. The objectives of this lecture are to provide an introduction to radiotherapy‐induced late effects including the governing biologic and technical factors to discuss techniques to minimize radiation exposures and risks and to speculate on future developments that will enable personalized risk‐optimized radiation treatments.

Learning Objectives:

1. Understand sources of radiation exposure and risk of relevance to radiogenic related late effects following modern external beam radiotherapy.

2. Understand techniques to quantify radiation exposures and to predict the associated risks of late effects.

3. Understand techniques to minimize radiation exposures and risks using existing technologies.
TH‐D‐BRA‐03: Genetic Susceptibility Radiation Exposure and Risk of Second Primary Breast Cancer
Authors: Bernstein J
Published: August 2010

Background: Deficiencies in cellular responses to DNA damage can predispose to cancer. Ionizing radiation induces double strand breaks (DSB). Upon activation by DSB‐inducing agents ATM (for ataxia‐telangiectasia (A‐T) mutated) phosphorylates a large number of downstream targets including the products of several known breast cancer susceptibility genes (e.g. BRCA1 BRCA2 Chek2 p53). In this study we examine whether defects in these breast cancer susceptibility factors are associated with radiation‐induced induced breast cancers. Methods: The WECARE Study is a case‐control study nested within 5 population‐based cancer registries in the US and in Denmark. The 708 cases were women with asynchronous bilateral breast cancer (CBC) and the 1399 controls were women with unilateral breast cancer (UBC) individually matched to cases on year of birth race geographic region and date of diagnosis (interval). All participants were interviewed medical records were comprehensively reviewed and full genetic screening was conducted. For women who received radiation therapy (RT) absorbed radiation doses to quadrants of the (CB) were estimated using dosimetry reconstruction. Rate ratios (RR) and 95% confidence intervals were calculated using multivariable‐adjusted conditional logistic regression models. Results: The mean dose to the specific quadrant of the CB tumor was 1.1 Gy. Women <40 years of age who received >1.0Gy and with >5 year follow‐up had a 3‐fold increased risk of CBC (95% CI‐1.1–1.8). The RR of CBC associated with carrying a BRCA1/2 mutation was 4.2 (95% CI=2.8–6.1); however among carriers radiation was not associated with risk. Among women carrying rare ATM missense mutations the risk of developing CBC was slightly increased but was significantly elevated among women treated with RT and strongest for mutations selected on their likelihood to disrupt structure. Conclusions: Risk of radiation‐associated CBC was inversely related to age at exposure and dose dependent. A subgroup of rare mutations may increase risk of CBC among women with early onset breast cancer treated with RT. However the fraction of CBC attributed to this is quite small suggesting that radiation contributes little to the already high risk of CBC associated with carrying these breast cancer susceptibility factors.

Learning Objectives:

1. Understand the role of DSB in CBC

2. Understand the basic study design of the WECARE Study

3. Understand the issues relating to genetic susceptibility and CBC risk
TH‐D‐BRB‐02: Improving the Accuracy of Monte Carlo Spread‐Out Bragg Peak Treatment Head Models Using Beam Current Modulation Optimization
Authors: Bednarz B , Lu H , Engelsman M , Paganetti H
Published: August 2010

Purpose: For challenging clinical cases Monte Carlo methods can help to verify the accuracy of proton beam planning results based on the pencil beam algorithm. However the use of Monte Carlo methods as a verification tool requires an accurate model of the proton fields generated in the treatment head. This paper presents a novel approach to improve upon the achievable accuracy of Monte Carlo models of proton beam treatment heads. We will also demonstrate the usefulness of this approach by presenting commissioning results of two treatment head models at our facility. Methods and Materials: The achievable accuracy of our treatment head model was examined by quantifying the impact of uncertainties in material and beam parameters on SOPB dose distributions. A novel approach to improve this accuracy was developed by optimizing the beam current modulation function defined in our Monte Carlo model to produce clinically acceptable SOBP dose distributions. Finally this method was utilized for the commissioning two models of SOBP proton beam treatment heads at our facility. Results: Uncertainty in material density led to the largest impact on the SOBP dose distributions (less than 4%). The impact of mean ionization potential uncertainties was smaller (less than 2%). We did not detect a statistically significant influence of clinically relevant beam energy spreads and spot sizes on the SOBP dose distribution. The optimization of our beam current modulation functions allowed us to fully commission two treatment head models at our facility. Conclusion: Several proton beam therapy centers are now operational or being planned and constructed which promises the future need for Monte Carlo modeling of proton beam therapy treatment heads. The methodology and results presented in this paper will help accommodate the commissioning of new Monte Carlo simulated treatment heads.
TH‐D‐BRB‐03: Monte Carlo Simulations of Beam Characteristics for a Compact Plasma Proton Accelerator
Authors: Constantin M , Constantin D , Perl J , Keall P , Poehlmann F , Rieker G , Cappelli M
Published: August 2010

Purpose: To (1) develop Monte Carlo applications for the geometry and particle transport in the treatment head of a compact coaxial plasma proton accelerator and (2) quantify the sensitivity of the output particle flux and dose distributions on the energy and angular spread of the input proton phase space. Method and Materials: Geant4 v4.9.3 was employed to simulate a plasma proton treatment head geometry including the beam collimator the magnetic field region and the energy selector. The energy spectrum assumed a Gaussian distribution centered at Emax=200MeV and the full width at half maximum (FWHM) was 0% 12.5% 25% 37.5% and 50% of Emax. The angular spread of the input proton beam was considered to be 0° 15° and 20° respectively. Flux and dose calculations were performed using a phase space implemented at the energy selector exit plane and a voxelized water phantom respectively. Results: For a fixed angular spread the output particle flux is fairly constant as the energy spectrum becomes broader while for a fixed energy spread the flux decreases significantly with increasing angular spread. The decrease is 10 times for 15° and 40 times for 20° angular spread. Dose measurements show that 200MeV protons even with a broad energy spectrum are preferable to photons when low entrance dose and conformal distal edge falloff are desired. The energy spread translates into a spread out Bragg peak used clinically without the introduction of any scattering devices in the beam path. Conclusions: This study shows that the delivered proton flux is highly sensitive to the angular spectrum of the input plasma accelerated protons and dose is sensitive to the spread of the energy spectrum. Monte Carlo simulations of beam characteristics for compact plasma proton accelerators provide important design parameters for the development of the next generation proton therapy units.
TH‐D‐BRB‐04: Ion Chamber Dosimetry Modification under Strong Magnetic Field Conditions
Authors: Koren S , Price R , Tafo A Guemnie , Veltchev I , Fourkal E , Ma C
Published: August 2010

Purpose: To examine the dose response of an ion chamber in an external magnetic field and to simulate the energy deposition using the Monte Carlo technique. Method and Materials: This work investigates the response of a 0.6cm3 Farmer chamber to an 11.17 mCi 137Cs source under the influence of a 1.5 T magnetic field on a GE MRI scanner. A wooden frame was designed that allowed varying field direction measurements while keeping the source to chamber axis distance constant. Monte Carlo simulations were conducted using FLUKA a particle physics transport package to score the energy deposition and the average electron track length inside the cavity. Results: Higher chamber current readings were obtained when a transverse (to chamber central axis) magnetic field was applied compared to zero B field conditions. Lower readings were obtained when a longitudinal field was present. A 4.8% increase was observed for the transverse field measurements and negative voltage polarity while a 3.5% decrease was measured for the longitudinal case. The positive polarity measurements showed a 3.7% increase and an 11.5% decrease in transverse and longitudinal fields vs. a 4.0% increase and a 6.0% decrease found through Monte Carlo simulations. The average track length increased by 11.0% and decreased by 6.8% in transverse and the longitudinal fields.Varying the electric field applied to the electrodes showed no significant changes in chamber response. Conclusion: The dose response of a Farmer chamber in an external magnetic field varies with the average charged particle trajectory length. The average trajectory depends on the B field magnitude and direction and on the energy spectrum of the primary photon beam. Thus an alignment with the B field direction would be essential. Smaller cavity chambers are expected to be affected less under B field conditions and should be investigated in the future.
TH‐D‐BRB‐07: Improving Computational Efficiency in Monte Carlo Simulations of a Passive Scattering Proton Therapy Treatment Head
Authors: Cortes‐Giraldo MA , Quesada JM , Gallardo MI , Paganetti H
Published: August 2010

Purpose: To increase the computational efficiency of the Monte Carlo simulation of a passive scattering proton therapy treatment head during the generation of a phase‐space file. Method and Materials: Geant4 Monte Carlo toolkit was used to simulate the transport of particles through the treatment head of a passive scattering proton therapy machine. With this application we have studied the impact that different aspects have on the time spent during the creation of a phase‐space file. We have mainly been focused on discarding primary protons that unlikely will reach the phase‐space plane. Further a simplified and equivalent model of the ionization chambers within the nozzle changes in the production cut values for secondary particles and the physics models included were also considered. Results: most of the time is reduced by discarding the tracking of protons that will not reach the phase‐space plane. For a 25‐cm‐diameter snout the average saved time is about 4% whereas a 30% of the time is saved for a typical case using a 12‐cm‐diameter snout. Moreover a simpler and faster model of the ionization chambers reduces the time in 8–10%. However changes in the production cut values do not save a large amount of time provided that secondary particles are not being considered for tracking. In addition the kinetic energy distribution of the beam can be biased with non‐suitable production cut values. Conclusion: we have developed some techniques to increase the efficiency of the Monte Carlo simulation of passive scattering proton therapy nozzle with Geant4. In our typical case around 35% of the time is saved. The work presented here can be used in Monte Carlo simulations of other passive scattering proton therapy treatment heads. Time reduction should be investigated for each particular case.
TH‐D‐BRB‐09: Development of a GPU‐Based Monte Carlo Dose Calculation Code for Coupled Electron‐Photon Transport
Authors: Jia X , Gu X , Sempau J , Choi D , Majumdar A , Jiang S
Published: August 2010

Purpose: Monte Carlo (MC) simulation is broadly considered as the most accurate method for dose calculations in radiotherapy. However its efficiency still requires improvement for many routine clinical applications especially for online adaptive radiotherapy. The goal of this work is to develop a GPU‐based MC dose calculation code. Method and Materials: We have implemented the Dose Planning Method (DPM) MC dose calculation on GPU architecture under CUDA platform. The MC simulation is performed by treating each computational thread on GPU as independent computing units responsible for the complete history of a source particle. To test the accuracy of our GPU‐based MC dose calculation with respect to the original sequential DPM code on CPU we have performed MC simulations on phantoms with an electron or a photon beam. Results: In all testing cases the average relative uncertainties σD/ D are less than 1%. Results obtained from CPU and GPU are in good agreement with each other (The difference at more than 98% voxels is within 1% of the maximum dose in both cases). These results demonstrate the adequate accuracy of our GPU implementation for both the electron and the photon beams in radiotherapy energy range. A speed up factor of 4.5 and 5.5 times have been observed for electron and photon testing cases respectively using an NVIDIA Tesla C1060 GPU card against a 2.27GHz Intel Xeon CPU processor. Conclusion: This work demonstrates the possibility to speed up the intensive computation in MC dose calculation. However due to the inherent conflict between GPU architecture and the randomness in MC simulations algorithms should be carefully tailored to achieve high efficiency on GPU.
TH‐D‐201C‐01: Advancing an Integrated Overhauser‐Enhanced MRI (OMRI) ‐ Prepolarized MM (PMRI) System Toward Quantitative Longitudinal Studies of Tumor Hypoxia and Redox Status
Authors: Ahn K , Scott G , Stang P , Conolly S , Hristov D
Published: August 2010

Purpose: To advance the imaging performance of an integrated Overhauser‐enhanced MRI (OMRI) ‐ prepolarized MRI (PMRI) system to enable quantitative longitudinal imaging studies of multi‐faceted tumor environment by using both electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) Method and Materials: A field‐cycled OMRI‐PMRI system was further developed to achieve the sensitivity that identifies radiobiological hypoxia and redox status. A dedicated 5‐cm saddle coil delivered 154‐MHz EPR radiofrequency (RF) pulses to induce the Overhauser effect with a high EPR B1 efficiency. A 3‐cm 5.5‐MHz NMR Litz‐wire saddle coil concentric to the EPR coil achieved high signal‐to‐noise ratio with an efficient filling factor. B0 was at 5 mT 0.13 T 0.5 T for EPR irradiation NMR readout NMR prepolarization respectively. Gradient echo and multi‐spin echo pulse sequences were implemented using a custom MRI console to acquire images with minimal phase distortion. Trityl phantoms were prepared under normoxic and anoxic environment for pO2 calibration. Various amounts of ascorbic acid (AsA) were injected to the mixtures of trityl and nitroxide (3‐carbamoyl PROXYL) phantoms to characterize the redox sensitivity. Results: Oxygen resolution of 4.1 torr and 3.5 torr were obtained from 4‐min double power (0.3 32 W) spin‐echo OMRI (TR/TE 1600/30 ms) for pure deoxygenated 1‐mM and 2‐mM trityl phantoms. Trityl radicals were not reduced by AsA and did not alter the reduction decay rate of the nitroxides (−0.07/min −0.13/min for 5 10‐mM AsA). Saturation factor measurements at various EPR RF power levels indicated a feasibility of accurate pO2 calibration for the mixtures of trityl and nitroxide radicals. Conclusion: Our OMRI‐PMRI system is capable of multi‐parametric imaging sensitive to pO2 redox status proton T1 and T2. The imager is ready to acquire physiological information in small animals accurately co‐registered with diagnostic quality anatomic NMR images.
TH‐D‐201C‐03: Correlation between MR Diffusion Tensor Imaging Derived Dimensional Ellipsoid Ratio as a Function of Tissue Anisotropy and Multiple Sclerosis Induced Variation
Authors: Lin L , Zhong J
Published: August 2010

Purpose: The diffusion fractional ellipsoids derived in ratios ((XMS −XNC)/XNC) are compared from both the Monte Carlo simulation and the deviated diffusion profile between normal brains and Secondary Progressive Multiple Sclerosis (SPMS) patients. We construct a map to evaluate the water diffusion in (1) standard sorted (2) non‐sorted and (3) normalized space of directional diffusivity and diffusion anisotropy indices. Method and Materials: The sensitivity coefficients are derived analytically between the anisotropy indices and diffusivities in the symmetric prolate λ1>λ2=λ3 and oblate λ1<λ2=λ3 diffusion and non‐symmetric geometry. The contrast‐to‐scatter ratios are calculated from the Monte Carlo simulation conducted in Matlab (MathWorks Natick MA) in addition to the mean contrast comparison of diffusion tensor derived parameter from white and gray matter of a SPMS study acquired in GE Signa 1.5T scanner with 21 gradient weighted direction scheme TR/TE=10800/80ms FOV=24cm voxel size=1×1×3 mm3 matrix size = 128×128 and b = 1000 s mm−2. Statistical comparison was performed in SPSS (SPSS Inc Chicago Illinois) to determine the significant Pearson correlation and difference of both within and across diseased and normal fiber bundles. Results: The sensitivity of the diffusion anisotropy indices as expressing from a ratio of standard deviation to magnitude/average is higher than the diffusivities in low anisotropy region. The diffusion ellipsoid of low anisotropy tissue is observed to be prolonged as SNR<20. The contrast‐to‐scatter ratio of FA decreases slightly with increasing anisotropy for SNR>20. Conclusion: Sensitivity analysis is demonstrated as a standard to derive the dimensional ellipsoid ratio as a function of anisotropy level and tissue type. A multiple sclerosis induced oblate ratio ellipsoid was observed in both of the genu and splenium corpus callosum while prolate ratio was found in the internal capsule and thalamus. In contrast both the radial and axial diffusivity decrease in the caudate nucleus.
TH‐D‐201C‐05: Monitoring Response of Liver Cancer to Targeted Radiation Therapy with a Novel 31P/1H MRS Coil
Authors: Panda A , Jones S , Sandrasegaran K , Dydak U
Published: August 2010

Purpose: To present a novel multi‐channel dual‐tuned 31P/1H MRS coil which allows for non‐invasive acquisition of in‐vivo phosphorus (31P) spectroscopy data from the whole liver. We hypothesize MRS data collected with this coil can improve the assessment of early tumor response to targeted radiation therapy. Method and Materials: A novel dual‐tuned 8‐channel 31P/1H coil for a Siemens 3T Tim Trio whole Body MRI scanner was designed and validated. The coil consists of two plates placed anterior and posterior of the patient's torso with four 31P receive elements (24×20 cm2) each. Furthermore each plate has one 31P transmit element and one 1H transmit‐receive element. Thus the coil allows for 31P MRS conventional MRI and 1H MRS during the same scan session. For our clinical study the 31P MRS data was acquired with a 2D slice selective free‐induction‐decay (FID) sequence using the following parameters: TE 2.3 ms TR 1 s field of view (FOV) 400×400×30 mm3 nominal voxel size 25×25×30 mm3 30 weighted averages. Each free‐induction‐decay (FID) was acquired with 2048 points over a bandwidth of 5000 Hz. The resulting scan time was about 25 min. Results: In vivo 31P liver spectra and 1H MRI images of the entire liver were successfully acquired in healthy volunteers and patients undergoing targeted radiation therapy. The optimized 31P MRS sequence allowed for identification and quantification of ATP phosphomonoesters (PME) phosphodiesters (PDE) and inorganic phosphate (Pi) metabolites throughout the liver on an axial slice. Metabolic differences between healthy and malignant liver tissue were clearly identified. Conclusions: We have shown that our novel 31P/1H MRS coil allows for assessing 31P metabolites in lesions located in deep tissue while being able to run conventional MRI imaging scans during the same scan session.
TH‐D‐201C‐07: A Quantitative Approach to Extracting Magnetic Susceptibilities of Small Cylindrical Objects from Clinical MRI Sequences
Authors: Hsieh C , Cheng Y , Haacke E
Published: August 2010

Purpose: Changes of venous blood oxygénation level lead to direct changes in the magnetic susceptibility of veins. The oxygénation level reflects the physiological state of a given vein. Therefore susceptibility quantification of veins has been a strong interest in MRI [1]. Here we will demonstrate a general approach to extracting magnetic susceptibilities of narrow cylindrical objects and veins at arbitrary orientations from only two or three echoes of a standard 3D gradient echo sequence. Method and Materials: Our previous work [2] has accurately quantified effective magnetic moments of given cylindrical objects. If an object has no MR signal its volume and susceptibility can be further determined [2]. When an object of interest (e.g. vein) has an MR signal the susceptibility of the object and its volume may be uniquely quantified from our CISSCO method applied on images acquired with three different echo times. Simulations and phantoms of Gd‐DTPA doped gel cylinders with diameters less than 5 pixels at arbitrary orientations were imaged at 1.5T. Several small isolated human cerebral veins were also measured from MR images. The uncertainties of magnetic susceptibilities were quantified by the error propagation method. Results: Differences of measured susceptibilities in simulations at echo time (TE) 14ms are within 15% of the input susceptibility (1 ppm). These differences agree very well with the uncertainties estimated from the error propagation method. The measured susceptibilities of diluted Gadolinium cylinders from echo time 14 ms images have uncertainties less than 15% estimated from the error propagation method. The measured susceptibilities of veins agree with the textbook value [3] within 16%. Conclusion: Simulations phantom studies and in‐vivo measurements demonstrate our approach can be used to accurately quantify the magnetic susceptibility of a given narrow and long cylindrical object.
TH‐D‐201C‐08: Multi‐Modal MRI SPECT and CT Imaging of Theranostic Nanoplatforms
Authors: Reynoso F , Gultepe E , Jhaveri A , Kulkarni P , Gershman B , Ferris C , Campbell R , Harisinghani M , Sridhar S
Published: August 2010

Purpose: The development of non‐invasive imaging techniques for the assessment of cancer treatment is rapidly becoming highly important. Magnetic Cationic Liposomes (MCL) that carry a cargo of anti‐cancer drugs and magnetic nanoparticles that will selectively target primary and metastatic cancer tumors deliver drugs to them and visualize their effects through magnetic resonance imaging (MRI) single photon emission computed tomography (SPECT) and fluorescence spectroscopy. The aim of the present study is to evaluate MCL as a versatile theranostic nanoplatform for enhanced drug delivery imaging and monitoring of cancer treatment. Materials and Method: Poly‐ethyleneglycol (PEG) coated cationic liposomes are loaded with superparamagnetic iron oxide nanoparticles (SPIONS) and tagged with the radioisotope Indium‐111. MCL was administered to SCID mouse with metastatic (B16‐F10) melanoma grown in the right flank. Pre‐injection and post‐injection MR and SPECT/CT images were used to assess response to magnetic targeting effects and tumor and organ distribution. Results: Tumor signal intensities in T2 weighted images decreased an average of 20±5% and T2* values decreased and average of 14±7ms in the absence of magnetic targeting. This compares to an average signal decrease of 57±12% and a decrease in T2* relaxation times of 27±8ms with the aid of external magnet showing up to 2‐fold greater accumulation by magnetic targeting. SPECT/CT images showed the localization and distribution of MCL in the tumor. Conclusion: MR SPECT/CT and biodistribution analyses clearly show the efficacy of MCL as MRI contrast agents prove the use of magnetic guidance and demonstrate the potential of MCL as agents for imaging guidance and therapeutic delivery.
Sci—Thur PM: YIS — 02: Intraoperative Guidance for Minimally Invasive Abdominal Surgery Using Fused Video and Ultrasound Images: A Phantom Study
Authors: Cheung CL , Wedlake C , Moore J , Pautler SE , Peters TM
Published: August 2010

Many abdominal surgery procedures are now performed minimally invasively. We consider tumour resection, where surgeons use a laparoscopic camera to view the organ surface and a laparoscopic ultrasound (US) probe to visualize the tumour to plan and perform the excision. Conventionally, images are displayed separately and are typically presented in 2D. Therefore, the surgeon has to look back and forth between the images and mentally map the US onto the video to determine the tumour location relative to the surface. Furthermore, the 2D nature of the images decreases depth perception. To address these limitations, we developed an augmented reality visualization that fuses images in a common 3D environment. Instruments were tracked using sensors spatially identified with a magnetic field generator. Through calibration, their image locations were determined in real time. The accuracy of the camera and US calibrations was determined both relative to the tracking system and to each other using target localization. We evaluated the efficacy of the fusion with a phantom experiment. A surgeon performed tumour resections on polyvinyl alcohol‐cryogel phantoms under the guidance of the conventional visualization and the fusion system presented in 2D and in 3D. The target localization error was 1.20±0.08mm for the camera, 1.85±0.14mm for the US, and 2.38±0.11mm between the camera and the US. Early results demonstrate a faster resection planning time using fusion compared to the conventional setup while maintaining similar margin accuracy. This study supports the implementation of fusion for guidance of time‐sensitive resection tasks performed under conditions of warm ischemia.
Sci—Thur PM: YIS — 03: Design and Performance Evaluation of Detector Modules for Positron Emission Mammography Imagers
Authors: Cuddy SG , Green D , Reznik A , Rowlands JA , Taghibakhsh F
Published: August 2010

Positron Emission Mammography (PEM) is a valuable molecular imaging technique used to visualize to both invasive and pre‐invasive lesions in the breast. While maintaining spatial resolution of 1–2 mm, a reduction of patient dose is required in order to use PEM in clinical metastatic cancer prevention studies. We are working to enable depth of interaction (DOI) measurements using a detector module design with photodetectors on either end of a scintillation crystal array to allow for increased detection efficiency. While typical dual‐ended readout designs couple one photodetector to either end of one crystal, we propose reducing readout requirements by enlarging the photodetectors such that one detector may readout one end of multiple scintillators. We simulated a dual‐ended detector module with photodetectors appropriately sized for 4 detectors to readout each end of a 3×3, 5×5, and 6×6 scintillation crystal array. Our work found that detector modules can accommodate up to 5×5 scintillators while achieving accurate crystal index identification and depth of interaction resolution of 1.33 mm. Based on this optimization, a detector module was assembled for both the single‐ and dual‐ended readout configurations using a 6×6 LYSO scintillation crystal array coupled to a 4×4 SiPM array. We successfully resolved all 36 scintillators in the single‐ended configuration verifying that large sized SiPM pixels may be used to accurately identify smaller pixelated scintillators. We are continuing this work for the dual‐ended configuration.
Sci—Thur PM: YIS — 05: Hyperpolarized Noble Gas Magnetic Resonance Imaging and Dynamic Spectroscopy of Rat Lungs
Authors: Fox MS , Ouriadov AV , Santyr GE
Published: August 2010

Magnetic Resonance (MR) imaging using hyperpolarized noble gases (HNG's), 3He and 129Xe, provide non‐invasive approaches for probing lung function and structure. In particular, measurement of HNG ventilated lung volumes (e.g., ventilation defects) and apparent diffusion coefficients (ADC) are useful for characterizing chronic obstructive pulmonary disease (COPD) and emphysema. Of particular interest, hyperpolarized 129Xe also dissolves in the lung parenchyma and blood compartments, offering an interesting palette of potential biomarkers of pulmonary disease, including quantifying xenon diffusing capacity in inflammatory disease and may be useful for assessing pulmonary perfusion. 129Xe dissolved in tissue and blood experience large chemical shifts and can be selectively saturated and allowed to recover as a function of delay time as in the chemically selective saturation recovery (CSSR) technique. CSSR has previously been used to study surface‐to‐volume ratio (S/V) and diffusing capacity of xenon (DXe) in the lung which is analogous to diffusing capacity of carbon monoxide. In this work, the 129Xe CSSR technique is used to measure S/V ratios and Dxelp in whole healthy rat lungs as a function of ventilated lung volume assessed with 3He MR imaging. The data follow theoretically predicted trends for Ttr, S/V and DXeLP. In parallel to this study, 3D 129Xe imaging was also investigated and compared to 3He for lung volume assessment in an effort to remove the reliance on 3He which is costly and scarce. Absolute ventilated volumes (|VLV|) derived from preliminary results for 3He and 129Xe were 9.74 mL and 9.14 mL respectively for a pressure of 9.1cmH2O.
Poster — Thur Eve — 02: Evaluation of Cross‐Talk for Dual‐Isotope Myocardial Perfusion Imaging Using a New Dedicated Cardiac CZT SPECT Camera
Authors: Wells RG , Vanderwerf K , Ali I , Ruddy TD
Published: August 2010

Myocardial perfusion imaging (MPI) with single‐photon emission computed tomography (SPECT) is an important tool in the clinical management of heart disease. Simultaneous dual‐istope imaging offers a means to greatly reduce the time required for this test, but is limited by interference between the signals of the two isotopes. Newly developed dedicated cardiac SPECT cameras based on CZT detectors may reduce the interference between isotopes due to improved energy resolution. Our objective is to measure in clinical patients the magnitude of cross‐talk expected for simultaneous perfusion imaging with Tl‐201 and Tc‐99m‐tetrofosmin on a new CZT‐based multi‐pinhole dedicated cardiac SPECT camera. We retrospectively examined 25 matched pairs of Tl‐201 and Tc‐99m‐tetrofosmin patients. Reprocessing the listmode data, we determined the cross‐talk fraction for typical energy windows as well as for a Tc‐99m energy window that was reduced from 20% to 12%. Two protocols were considered: Tl‐rest/Tc‐stress and Tc‐rest / Tl‐stress. Cross‐talk into the Tl window was 74% and 36% respectively for the two protocols. Cross‐talk into the 10% Tc‐99m window was 2.4% and 11% respectively. The cross‐talk into the Tc‐99m window was reduced by 25% using a +/−6% window. Cross‐talk between Tc‐99m‐tetrofosmin and Tl‐201 has been assessed for the new dedicated CZT‐based cardiac SPECT cameras and the improved energy resolution of the CZT detectors decreases cross‐talk interference.
Poster — Thur Eve — 03: A Monte Carlo Investigation of the Effects of a Novel In Vivo Transmission Detector on a 6 MV Photon Beam
Authors: Asuni G , McCurdy B
Published: August 2010

The effect of a transmission detector (TRD), a novel IMRT quality assurance tool to be used for in vivo dose measurements, was investigated. As a scattering material, the device will be a source of contaminant electrons and could potentially affect prescribed dose to patients during treatment. The goals of this investigation are to characterize the effect of the TRD on the clinical photon beam including IMRT fields, using Monte Carlo simulation. The linear accelerator head and the TRD were modeled using BEAMnrc. Particles scored at 70 cm and 100cm SSD for different field sizes (i.e. 5×5 cm2, 10×10 cm2, and 20 × 20 cm2) with and without the TRD were separated according to where they were created in the linac head. In addition, two IMRT fields with and without the TRD were simulated and their respective absolute dose distributions were compared. Without the TRD, air is the major source of contaminant electrons. When TRD is used, it absorbs nearly all the incident contaminant electrons, while becoming the major source of contaminant electrons. For both IMRT fields, the percentage dose differences of the calculated absolute doses with and without TRD at the isocenter were found to be within uncertainty of the measured transmission factor for the TRD. Although a major source of contaminant electrons, the TRD does not introduce excessive electron contamination into a clinical 6 MV photon beam and is therefore suitable for in vivo dose measurements if fully commissioned as an IMRT quality assurance tool. Research partly sponsored by IBA Dosimetry.
Poster — Thur Eve — 06: Radiochromic Film Densitometry with Vista15 Optical Cone Beam CT Scanner
Authors: Babic S , Jordan K
Published: August 2010

Purpose: To examine the performance of a scatter corrected commercial optical cone beam CT scanner, Vista15™, adapted for radiochromic film dosimetry. Methods: A slotted film mask adjacent to the EBT2 film was used to generate alternating open and dark areas. Three images were acquired with the mask centered along the optical axis and offset +/−0.7cm. The masked transmission images were processed by first forming composite images from the open and shadow areas of the three image sets. The composite shadow image was subtracted from the corresponding open image to create a “glare‐free image”. Net optical density (OD) images were generated by calculating −log10 (corrected post/corrected pre image). The calibration dose response in EBT2 film using multiple 4MV photon fields and a single 12MeV electron field was measured. Results: In the corrected data, net OD increased and the buildup region mirrored actual 12MeV dose deposition in water. This trend was also observed in the multiple 4MV photon field calibration data. From comparing the two calibration techniques, a discrepancy in net OD of up to 4% was observed. This suggests that EBT2 film users should have a consistent method for calibrating the dose response. Conclusions: The emission spectrum of Vista15™ designed for readout of radiochromic gels and plastics overlaps the absorption peak in EBT2 films, thus, making this scanner convenient and economical for both planar and 3D dosimetry. A method for veiling glare correction is promising but a more complex multiple grid approach will be needed in order to achieve quantitative densitometry.
Poster — Thur Eve — 08: Dosimetric Comparison Study of Rotational and Static IMRT Treatment Plans for the Prostate
Authors: Blais A , Leszczynski K , Lederer E
Published: August 2010

It has been reported that for certain clinical applications, Rotational Intensity Modulated Radiation Therapy (R‐IMRT) techniques such as Volumetric Modulated Arc Therapy are capable of improved target dose coverage and shorter delivery time when compared to static, step‐and‐shoot IMRT. Five similar early stage prostate cases were used to generate R‐IMRT and static IMRT plans. The R‐IMRT plans consisted of 72 single‐segmented 6MV beams, equally spaced with beam angle separations of 5 degrees. The static IMRT plans employed 7 multi‐segmented 6 MV beams. Both types of plans were optimized with the direct machine parameter optimization algorithm using the same set of optimization objectives. Dose volume histograms were obtained for both types of plans and were comparatively evaluated based on target coverage and dose to organs at risk. For 3 out of 5 cases, target coverage was found to be better with R‐IMRT: standard deviations were consistently lower, and V95 values were equal or better. Critical structure sparing was better for static IMRT with mean dose, V50 and V75 values for the rectum and bladder consistently lower for the majority of the 5 cases. In cases where target coverage was better for static IMRT, the critical structure sparing was better for R‐IMRT. Treatment time was approximately 3 times as long for R‐IMRT due to the lack of dynamic MLC's on the Primus linac. It was found that R‐IMRT can provide improved target coverage in certain applications when compared to static IMRT, however critical structures may receive a slightly higher dose with this technique.
Poster — Thur Eve — 09: Effects of Small Sample Size on Diffuse Reflectance Spectroscopy for the Identification of Brain Tumours
Authors: Cappon D , Hayward J , Farrell T , Fang Q
Published: August 2010

An optical system using diffuse reflectance spectroscopy (DRS) and time‐resolved laser induced fluorescence spectroscopy (TR‐LIFS) is being developed to identify surgical margins during brain tumour resection. Since initial trials will be performed ex vivo on small samples, we investigated our ability to perform DRS for these small sample volumes. We examined both the effects of decreasing sample volume on the DRS signal and decreasing probe size on our ability to recover optical properties. Sample volume effects were studied by performing DRS measurements on bovine brain tissue samples of various sizes and comparing the signals to those for very large samples. A decrease in DRS signal strength was observed at sample volumes of less than 500 mm3. Probe size effects were studied using Monte Carlo simulations to obtain the spatially‐resolved reflectance using the optical properties of human brain tissue. Varying amounts of noise were added to the reflectance, and optical properties were recovered by fitting to Monte Carlo generated reflectance curves. The recovered properties were compared to their actual values as the maximum radius used for fitting was reduced. Our ability to recover the absorption coefficient was improved when fitting to absolute reflectance data.