bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐557: Optimal Energy for Partial Breast Irradiation Using a 360° Coronal Plane Rotation Technique
Authors: Becker S , Jozsef G , De Wyngaert J
Published: July 2008

Purpose: To determine the optimal energy for treating partial breast irradiation in the prone position with a novel treatment technique. This method would rotate 360 degrees around the patient's breast on a coronal plane compared to the standard transverse plane. Method and Materials: Partial prone breast patients were planned using a simulated helical tomotherapy with a rotated delivery plane. 17 evenly spaced IMRT fields were place around the breast in the coronal plane. Fields were setup to cover the entire PTV. Plans using energies of 6MV, 4MV and Cs‐137 (simulating ∼2MV) were created. The dose was prescribed according to RTOG protocol 0413 such that 95% of the PTV received 38.5 Gy. Optimization was performed to achieve target coverage and minimize normal breast tissue such that <60% of the normal breast tissue received <50% Rx dose and <35% received the full Rx dose. Optimization was not required on the lungs, heart or contralateral breast since no beams intersected them. Results: Coverage of the target was not affected by the choice of energy. All energies easily covered the PTV. The dose to the skin and normal tissue depended on both the size of the breast and energy of the fields. For the average case 4 MV proved to be the optimal energy for minimizing the dose to the normal breast tissue and skin. Conclusion: Due to the smaller size of the breast, exit dose plays an important role in the dose the normal breast tissue and skin. For a standard breast size optimal ratio of the surface dose to the exit dose was a 4 MV beam. The dose differences however were small enough that optimal energy maybe be determined by cost or shielding requirements.
SU‐GG‐T‐558: OPTIS2 ‐ PSI's New Ocular Proton Therapy Facility
Authors: Heufelder J , Verwey J , van Goethem M‐J , Zografos L , Jermann M , Goitein G , Hug E
Published: July 2008

Since 1984 nearly 5000 patients with eye tumors, primarily ocular melanomas, were treated by a 72 MeV Phillips cyclotron within the OPTIS program (local tumor control 98%@10y). In the frame work of the PROSCAN project a dedicated superconducting cyclotron (COMET) is in clinical operation since February 2007. The aim of OPTIS2 project, an entirely new facility for the treatment ocular tumors with COMET, is to match the clinical success of OPTIS. Using the COMET/PROSCAN facility the beam intensity at the start of the OPTIS2 nozzle is 30 times lower than that currently used at the OPTIS facility. If we would keep using the OPTIS nozzle the treatment time would increase dramatically. Therefore, the new nozzle utilizes a double scattering technique with multiple‐ring second‐scattering foils which increases the nozzle efficiency by factor of 10, keeping the maximum treatment time under one minute. Due to the difference in scattering techniques the OPTIS2 and OPTIS beams are not identical. But the major characteristics, distal‐ and lateral‐ dose fall‐off are comparable. The flatness and symmetry have actually been improved. In OPTIS2 reliance on a single analog X‐ray film provider and extensive operator experience will be diminished by introducing digital imaging and computer aided semi‐automatic patient positioning. A new imaging and patient positioning concept has been developed, bringing together techniques and software already clinically tested at the Center de Protontherapie Orsay (France) and the Hahn Meitner Institut (Germany). OPTIS2 is designed and built from scratch, providing a continuation of the existing proton therapy program OPTIS, with comparable beam characteristics, whilst obtaining its protons from COMET. Beam commissioning and system testing is currently underway. A first patient treatment is scheduled for summer 2008.
SU‐HH‐AUD C‐04: Improved Lesion Conspicuity in Dual‐Energy Imaging of the Chest: From NEQ to Observer Performance
Authors: Richard S , Siewerdsen J
Published: July 2008

Purpose: To derive Fourier metrics of imaging performance (e.g., NEQ) in dual‐energy (DE) imaging of the chest that agree with human observer performance and to employ the resulting theoretical framework to system optimization with respect to lung nodule conspicuity. Method and Materials: The NEQ was computed using cascaded systems analysis extended to DE imaging and combined with a Fourier description of imaging task to yield an estimate of observer SNR (i.e., detectability index and AZ). Theoretical results were compared to human observer performance assessed in multiple alternative‐forced choice (MAFC) tests across a broad range of imaging conditions. The modeled observer SNR was used as an objective function for optimizing DE acquisition techniques and decomposition algorithms. A method for optimizing system performance for multiple imaging tasks was also investigated. Results: Theoretical calculations of the DE NEQ agreed well with measurements, and the task‐based detectability index was found to provide a strong predictor of human observer performance. Results identified [60/150] kVp as the optimal energy pair, with a weak dependence on high kVp. Optimization of the DE decomposition algorithms yielded significant improvements in lesion conspicuity — e.g., improving detection from barely visible (AZ <0.7) to highly conspicuous (AZ ∼1) at fixed dose to the patient. Optimal dose allocation (the fraction of total dose delivered in the low‐energy image) was found to range significantly — from 0.22 to 0.76 — depending on the choice of decomposition algorithm and imaging task. Conclusion: A theoretical model of DE imaging performance was derived and validated in comparison to human observers. The resulting framework provides a valuable guide to system optimization over a wide range of acquisition and decomposition conditions, yielding significant improvement in lung nodule conspicuity.
MO‐A‐AUD C‐01: Practical Considerations for Respiratory Colarated CT Imaging and Target Volume Delineation
Authors: Mutic S
Published: July 2008

Accurate and conformal treatment of tumors in abdomen and thorax is challenging due to respiratory related motion. Respiratory corralled CT imaging combined with gated treatment delivery can improve both accuracy and conformality of delivered dose distributions. Implementation of respiratory correlated imaging and treatment delivery can be performed in multiple ways and understanding of different techniques and technical challenges is critical for efficient and safe clinical implementation. Formal recommendations for commissioning and clinical use of this technology is scarce. Inadequate evaluation and understanding of these systems can lead to significant treatment errors. This presentation deals with practical issues of respiratory correlated CT imaging and commissioning. Examples of some commonly seen image artifacts are also discussed. Furthermore, contouring based on respiratory correlated images is discussed, again with examples of some of potential pitfalls and artifacts.

Education Objectives:

1. Commissioning process for respiratory correlated CT imaging and delivery techniques.

2. Use of respiratory correlated images for target delineation.

3. Common image artifacts and contouring errors seen with respiratory correlated imaging.
MO‐SAMS‐332‐01: The Principles of Quantitative MRI
Authors: Clarke G
Published: July 2008

The applications of magnetic resonance imaging (MRI) in biomedicine are undergoing rapid evolution. Typically used to produce images that are viewed and subjectively rated by a radiologist, MRI is now being utilized as a scientific apparatus capable of making noninvasive measurements in living tissues. With care, a significant number of physical and biological measurements can be performed and related to individual pixels and groups of pixels in the MR image. This presentation will address the challenges in obtaining quantitative data from MRI.

The presentation will review the principles of good practice in quantification, including quality assurance, MR data collection, and analysis. Limits on precision and accuracy are discussed and solutions proposed. Three major topics are considered. First, the signal collection process in MRI will be reviewed concentrating on geometrical relationships derived from MR images and signal‐to‐noise considerations. Then, physical sources of quantitation errors in MRI will be considered; especially resonant frequency offsets, radio frequency (RF) attenuation, dielectric phenomena and eddy current effects. Third, common quantitative measurements using MRI will be explored. The principles underlying the measurement of each quantity are given along with their biological and medical significance and practical approaches for achieving their accurate measurement. Shortcomings of the measurement processes and a summary of potential clinical applications are also discussed. Pathological and developmental observations will be also compared with MRI‐derived quantities where appropriate.

This presentation is intended as an introduction to the field of measurement in MRI for anyone who desires to use the scope of modern measurement techniques to quantitatively determine the consequences of disease, its development or its reaction to therapy from MR images. It will be of interest to medical physicists who are considering undertaking quantitative work with MRI, as well as those already in the field.

Educational Objectives:

1. Appreciate the clinically important quantities that can be measured with MRI.

2. Be familiar with the methods and techniques used for quantitative MRI.

3. Have a basic understanding of the limits on precision and sources of error in quantitative MRI.
MO‐B‐352‐01: The Clinical Perspective — Multimodality and Multidimensional Imaging
Authors: Vannier M
Published: July 2008

Modalities like optical, CT, MR, PET/SPECT and US are used separately, but can be combined. Multimodality imaging is necessary when the results of two (or more) modalities differ, and each does something useful but not everything that's required. We will consider several practical examples: residual or recurrent tumor after treatment, eloquent cortex in the brain when a lesion is nearby, drug effect in situ — especially for cytostatic agents, control of thermal ablation, vulnerable plaque, evaluation of gene therapy, and assessment of revascularization benefits depending on tissue viability. All of these scenarios can be detected in one modality, where another provides a morphologic reference useful for guiding therapy.

Not only are imaging modalities synergistic, but their performance can be altered and utility extended using exogenous agents, such as contrast media, radiopharmaceuticals, and other targeted compounds with desirable in vivo biological and physical characteristics. Optimizing the combination of modalities, agents, data acquisition, image reconstruction, visualization and analysis can be challenging, but may provide unique capabilities that no single technique could offer.

We will evaluate the state‐of‐the‐art for combining modalities in animals and show how this could translate to clinical practice, recognizing the impediments of cost, complexity, reliability, crosstalk, and safety/regulatory restrictions. The need and potential for multimodality techniques and systems already far exceeds what's currently available, so we can identify some unsolved problems where the benefits are not yet available.

Educational Objectives

1. To understand the synergy between modalities (optical, CT, MR, PET/SPECT, US), contrast agents or tracer compounds, and post‐processing image analysis that provides multimodality and multidimensional capability.

2. To provide examples of how multimodality/multidimensional imaging can solve clinical problems in diseases of the brain, cardiovascular system, cancer, and for regenerative medicine.

3. To identify several unsolved problems where multimodality/multidimensional imaging may provide clinically useful solutions.
MO‐E‐332‐05: The Effect of Copper Beam Filtration On the Transmission of Scattered X‐Rays Through a Typical Lead Barrier
Authors: Larson S , Goodsitt M , Christodoulou E , Young R
Published: July 2008

Purpose: Standard use of copper beam filtration in modern cardiac catheterization and angiography systems can substantially change the x‐ray beam quality and ultimately have an impact on scattered x‐ray transmission through shielded barriers. A study was performed to investigate these effects. Method and Materials: Scatter was measured using broad‐beam geometry at 50 and 100 cm from the center of an 8″‐thick Lucite phantom with an 1800 cc ionization chamber. A Siemens Axiom Artis system was employed using 60, 81, 102 and 125 kVp with filtrations of 0, 0.1, 0.2, 0.3, 0.6 and 0.9mm of copper. The ionization chamber was wrapped in 1/16″‐thick lead to determine the transmission of scattered x‐rays through a typical shielded barrier. Results: Transmission at 125 kVp varied from 1.7×10−3 to 3.0×10−3 for beams with 0 to 0.9 mm of Cu, respectively. Similarly, transmission varied at 102 kVp from 1.2×10−3 to 2.2×10−3 and at 81 kVp from 7.1×10−4 to 9×10−4. Transmission at 60 kVp was about 7×10−4 for beams with 0 to 0.3 mm of Cu. Transmissions without Cu filtration at 125 and 102 kVp were measured to be about half the theoretical value reported by Simpkin and Dixon, which could result from variations in lead thickness. At 60 and 81 kVp transmissions without Cu filtration are more than an order of magnitude higher than that reported at 70 kVp by Simpkin and Dixon. Conclusion: Additional copper filtration can increase the barrier transmission up to a factor of two over unfiltered beams. However, it is unlikely that this amount of increase in transmission will significantly modify a shielding calculation. Further investigation is needed to determine the changes in typical workloads and scattered air kerma at different angles for these systems to understand the combined effect of these changes on barrier shielding calculations.
MO‐E‐342‐01: Nuclear Medicine Instrumentation
Authors: Turkington T
Published: July 2008

Nuclear Medicine instrumentation continues to progress, both hardware and software. Advances in PET/CT include increased PET sensitivity, respiratory gating, time of flight measurement, and improved image reconstruction algorithms that encorporate more physical effects into the acquisition model. Gamma cameras are incorporating new detector materials, and SPECT is being done with new acquisition geometries and reconstructed with new algorithms.

We will discuss new developments in nuclear medicine instrumentation, including ones that are currently available commercially and ones that are on the horizon.

Educational Objectives:

1. Understand three new developments in PET that have the potential to improve image quality.

2. Understand how new detector materials allow new acquisition geometries for SPECT.

3. Understand how physic effects in the acquisition process can be modeled in the image reconstruction process.

Research sponsored by GE Healthcare.
TU‐SAMS‐AUD B‐01: KV and MV Cone Beam CT Imaging for Daily Localization: Commissioning, QA, Clinical Use, and Limitations
Authors: Hammoud R , Miften M , Moseley D , Pouliot J
Published: July 2008

Three‐dimensional conformal radiotherapy (3D‐CRT), intensity‐modulated radiotherapy (IMRT), and body stereotactic radiotherapy (BSRT) allow for the generation of highly conformal dose distributions for patients with tumor volumes wrapped around or adjacent to critical structures. As a consequence of steep dose gradients between the target and organs‐at‐risk, precise localization of the target volume and surrounding normal tissue is essential. However, variations in patient setup and organ motion are limiting factors in the accurate delivery of radiation treatment with a high degree of precision. Recent online image‐guided RT techniques using kilo‐Voltage cone‐beam CT (kV‐CBCT) and Mega‐Voltage CBCT (MV‐CBCT) are now offering the opportunity to overcome these limitations and greatly improve treatment localization accuracy. These IGRT techniques using the latest imaging technologies represent an improvement over traditional techniques such as 2D portal imaging. It allows for the use of volumetric online imaging to account for organ motion and setup variation by providing multiple anatomical views of the patient during the full course of RT treatment. The selection of imaging modality and system to use in support of a treatment protocol is often a compromise between image quality, efficiency, availability, and dose.

Educational Objectives:

1. To review kV‐CBCT and MV‐CBCT imaging systems for daily localization including:

a. Commissioning, image quality, dose, registration process, and acquisition modes.

b. Clinical integration.

c. QA, stability over time, and downtime.

d. Standard clinical applications.

e. Novel clinical applications.

f. Technology evolution and future directions.
TU‐SAMS‐332‐01: Film‐Screen Mammography QA: What You Need to Know
Authors: Schueler B
Published: July 2008

The medical physicist provides a valuable service to mammography facilities by helping to ensure the production of high quality images at a low radiation dose. This presentation will describe the role of the medical physicist in mammography QA and equipment performance evaluation of film‐screen systems. Individual tests for both initial and annual equipment evaluations will be described. Special attention will be paid to potential pitfalls, common problems and ways to increase efficiency of the testing process.

Educational Objectives

1. Review medical physicist responsibilities in film‐screen mammography QA.

2. Learn about the specific requirements involved in testing for new equipment installations.

3. Review quality control procedures for annual equipment performance evaluations.

4. Learn about ways to streamline equipment performance evaluations.
TU‐B‐342‐01: SPECT/CT and PET/CT Dosimetry
Authors: Fahey F
Published: July 2008

This presentation will discuss the dosimetric factors associated with PET/CT and SPECT/CT including those associated with the administration of radiopharmaceuticals for both PET and SPECT and the specific factors associated application of CT in these hybrid modalities. The dosimetry of the application of these modalities to pediatrics will also be discussed. For SPECT, the dosimetry of the administration of radiopharmaceuticals typically used in SPECT as well as potential methods for maintaining these doses at reasonably low levels. In particular, myocardial perfusion imaging will be discussed. Also the use of new reconstruction techniques and how they may be used to lower the administered activity for some SPECT applications will be discussed. For PET, the dosimetry associated with the use of fluoro‐deoxy‐glucose (FDG) will be discussed including different technical approaches that may lead to lower administered activity. Lastly, the application of CT to both SPECT and PET will be discussed including the requirements for CT‐based attenuation correlation, anatomical correlation and diagnostic CT. Potential methods to reduce CT dose in these protocols will be discussed.

Educational Objectives:

1. Discuss 2 potential ways to reduce the administered activity in SPECT.

2. Describe 2 ways that the acquisition of PET can be modified to make it more efficient.

3. List 3 approaches that can be used to reduce the dose of the CT used in conjunction with PET and SPECT.
TU‐C‐AUD B‐03: A Comparison of Heterogeneity Correction Algorithms
Authors: Alvarez P , Molineu A , Hernandez N , Hall F , Followill D , Ibbott G
Published: July 2008

Purpose: To compare the measured dose distribution to the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center has constructed an anthropomorphic thorax phantom that includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was irradiated by 33 institutions with results that meet criteria established for the RTOG 0236 protocol. TLDs and radiochromic films were used as dosimeters within the target region. Institutions were asked to design plans using 3D‐CRT and IMRT techniques. The TLD dose was compared to the dose calculated by the TPS at the center of the target. Film response was normalized to TLD doses and a 2D‐gamma analysis comparison to the planned distribution was performed. Institutions whose irradiation of the phantom did not meet the RTOG 0236 criteria were not included. Results: A 2D‐Gamma analysis was done in the axial, sagittal and coronal planes through the PTV. 5% / 5mm criteria were applied. Due to limitations of the analysis software only the comparison over the axial plane is reported. 21 of the cases were planned with a superposition/convolution or AAA algorithm. For these cases, 92% ± 12% of the pixels in the analyzed region met the criteria. 12 of the cases were planned with a pencil beam or Clarkson algorithm. 74% ± 25% of the pixels meet the criteria for these cases. Conclusion: The superposition convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms.

Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.
TU‐C‐AUD C‐03: Teletherapy MicroRT Using a Commercial 192Ir Source
Authors: Low D , Izaguirre E , Deasy J , Mutic S , Hope A , Stojadinovic S , Diao X , Grigsby P
Published: July 2008

The prototype small‐animal irradiator (microRT) developed at Washington University utilizes the commercial 192Ir high‐dose rate (HDR) remote afterloader source in a teletherapy geometry. The system consists of a set of four Tungsten collimators (5.5 mm diameter hole) mounted to an Aluminum support tube. An HDR catheter is used to transport the source to the collimator and pre‐determined dwell positions center the source at the collimator hole. The mouse is placed on a couch that contains a series of drilled holes that act as fiducial localization marks visible on computed tomography (CT) imaging. For most experiments, the mouse is first anesthetized and placed on a couch. The couch is imaged using a commercial CT scanner (spatial resolution approximately 0.6 mm). The couch geometry is automatically registered in the treatment planning software, which was written in the Computational Environment for Radiotherapy Research (CERR) platform. The treatment planner determines the dose and adjusts the source‐to‐target distance to achieve the required field size and the target dose, coupled with the source strength, determines the irradiation time. The couch is mounted to a computer‐controlled three‐dimensional stage that positions the mouse to submillimeter accuracy. Advantages of the system include its relatively high precision, low fabrication cost, and straightforward and robust operation. Disadvantages include the need for having a commercial HDR source and the associated complexities of scheduling experiments, the relatively poor penumbra, and the steep depth‐dose behavior. The system works very well for parallel‐opposed fields to either the whole brain or hemi‐brain, and tumors grown on the mouse flank.
TU‐C‐AUD C‐05: Glimpse of 2058 Status of Small Animal IGRT
Authors: Jaffray D
Published: July 2008

The significant role of radiation therapy in the management of cancer requires that we advance our understanding of this powerful therapeutic modality. The advancements in imaging and radiation delivery technology promise to make this intervention more patient specific with design of therapy based upon biological image signals and, furthermore, routine redesign as the therapy progresses. This complex interplay between the radiotherapeutic insult and the evolving biological processes will stress current models of RT effect and, ultimately, the current weak models will limit the potential for full exploitation of RT. The development small animal irradiators represent an important initiative to improve our understanding of RT. These developments are occurring as the basic cancer research field is challenging in‐vitro and non‐orthotopic assessments of radio‐effect. Furthermore, image‐based methods of evaluating the microenvironment are being recognized as necessary inputs to normalize the results of RT intervention. These trends suggest that animal irradiation systems are likely to play a central role in the development of robust models of radiotherapy effect.
TU‐C‐351‐01: Design of Magnetic Resonance Imaging Protocol for Accelerated Partial Breast Irradiation in Prone Position
Authors: Ahn K , Hargreaves B , Alley M , Horst K , Daniel B , Hristov D
Published: July 2008

Purpose: Accurate delineation of tumor bed is prerequisite for an effective treatment of breast cancer with accelerated partial breast irradiation (APBI) technique. Magnetic resonance imaging (MRI) has high contrast mechanisms that could enable precise contouring of the lumpectomy cavity. We investigated practical issues pertinent to MR‐guided breast radiation therapy using customized pulse sequences. Method and Materials: Unilateral breast MR images were obtained from two healthy volunteers in prone position on a dedicated coil. Radiation therapists positioned the volunteers in reproducible setup using a waterproof marker. We acquired 6‐min 3D MR images to analyze setup uncertainty and fast 2D MR images of 0.5‐s temporal resolution to detect respiratory motion. An accurate 3D warping‐correction algorithm was evaluated and used to restore spatial fidelity from geometric distortions due to MR gradient non‐linearities. MR images of surgical clips as fiducial were obtained using pulse sequences designed to provide high signal from lumpectomy cavity. Results: Average breathing motion in the breast was found to be less than 0.5 mm in prone position. Setup deviations of 1 cm were observed between series of intended prone positioning. Rigid image registration based on local anatomy structure resulted in a residual error which was up to 5 mm at the peripheral region of the breast. Gradient‐induced non‐linearity led to 1 cm distortion in the uncorrected phantom image at the region 15 cm away from the main magnet axis. The 3D correction algorithm reduced the deviation to < 1 mm. We observed 4 mm signal void artifacts of surgical clips. Conclusion: We obtained MR images of suitable quality from volunteers using pulse sequences customized for lumpectomy site identification. MR‐guided APBI in prone position would require 5 mm uniform expansion of clinical target volume with the employment of an appropriate on‐board imaging technique.
TU‐C‐332‐05: Simulation of Ultrasound Two‐Dimensional Array Transducers Using a Frequency Domain Model
Authors: Rao M , Varghese T , Zagzebski J
Published: July 2008

Purpose: Ultrasound imaging with two‐dimensional (2D) arrays has garnered broad interest from scanner manufacturers and researchers for real time three‐dimensional (3D) imaging. Previously we described a frequency domain B‐mode imaging model applicable for linear and phased array transducers. In this study, we extend this model to incorporate 2D array transducers. Method and Materials: The pressure field for a 64×64 square array with element dimension of 0.15 mm and center‐to‐center spacing of 0.2 mm was calculated by applying the paraxial approximation to solve the 2D Rayleigh integral. We assume a rigid baffle, no apodization, a 2.5 MHz center frequency, and a speed of sound of 1540 m/s. A single transmit focus at 30 mm and dynamic receive focus with an F‐number of 2 was utilized. The 2D array model is compared with the widely used ultrasound simulation program FIELD II, which utilizes an approximate form of the time domain impulse response function. Results: Discrepancies between waveforms computed using our model and FIELD II are less than 4%, regardless of the steering angle for distances greater than 2 cm, yet computation times are on the order of 1/35 of those using FIELD II. Modern beam‐forming techniques such as apodization, dynamic aperture, dynamic receive focusing and 3D beam steering can also be simulated. The simulated beam patterns and point spread function images allow evaluation of beam properties for specific transducer parameters. Simulations of B‐mode images provide vivid demonstrations of the ability of 2D arrays with specific imaging parameters to detect lesions of a given backscatter contrast and size. Conclusion: The frequency domain approach provides an effective and feasible tool to model transmitted and pulse‐echo fields as well as B‐mode images for 2D array transducers.
TU‐C‐332‐10: Evaluation of Combined Effects of Target Size, Background Activity, and Respiratory Motion On 3D and 4D PET/CT Images
Authors: Park S , Ionascu T , Killoran J , Mamede M , Gerbaudo V , Chin L , Berbeco R
Published: July 2008

Purpose: In recent years, quantitative analysis of gated (4D) PET/CT images has been introduced for diagnosis, staging, and prediction of tumor response where internal organ motion is significant. However, the best methodology for applying 4D information to radiotherapy target definition is not currently well established. In order to accurately determine moving target volume, we have investigated the combined effects of target size, respiratory motion, target‐to‐background activity concentration ratio (TBR) on ungated (3D) and 4D PET images as well as gating methods. Method and Materials: Using a GE Discovery PET/CT scanner, a 3D‐PET scan corrected with a 3D attenuation map from 3D‐CT scan and a 4D‐PET scan corrected with matching attenuation maps from 4D‐CT were performed using spherical targets (0.5–26.5 mL) filled with in a NEMA IEC body phantom at different TBRs (infinite, 8, and 4). To simulate respiratory motion, the phantoms were driven sinusoidally in the superior‐inferior direction with amplitudes of 0, 1, and 2 cm and a period of 4.5 s. Recovery coefficients were determined on PET images. In addition, gating methods using different numbers of gating bins (1–20 bins) were evaluated by determining image noise and temporal resolution. Results: Signal loss in 3D‐PET images was measured from both the partial volume effect, due to the limited PET resolution, as well as respiratory motion. The results show that signal loss depends on both the amplitude and shape of respiratory motion. However, 4D‐PET successfully recovers most of the loss induced by respiratory motion. The 5‐bin gating method gives the best temporal resolution with acceptable image noise. Conclusion: The results based on the 4D scan protocols can be used to improve the accuracy of gross tumor volume definition in the lung and abdomen.
TU‐C‐342‐04: Advances in Endovascular Image‐Guided Interventions
Authors: Rudin S , Hoffmann KR , Bednarek DR
Published: July 2008

In a recent Medical Physics “Vision 2020” paper (Medical Physics 35(1): 301–309, Jan 2008), the authors reviewed the state of endovascular image‐guided interventions (EIGI) and offered some predictions for the future. Here we review the current status of the field and of some of these advances. First, endovascular devices (such as clot busting tools, stents and their catheter delivery systems, and blood flow modifiers) are becoming finer, more complex, and are enabling the replacement of invasive surgical procedures with minimally invasive EIGI procedures. Innovative methods of actuating motion at the catheter tip, such as the use of external magnetic fields, are being introduced. Second, along with improvements in devices, imaging systems that provide real‐time high‐resolution image guidance are being developed including a Solid State X‐ray Image Intensifier based on electron multiplying charge coupled devices (EMCCDs) that provide large on‐chip gain to overcome instrumentation noise such as that characteristic of current flat panel detectors. SSXIIs also have very high resolution capable of exceeding 10 lp/mm yet with no lag or ghosting. Third, the new high‐resolution region‐of‐interest (ROI) detectors can be used in combination with large conventional detectors for dual‐detector cone‐beam computer tomography (CB‐CT) to visualize ROIs within larger objects yet with minimal truncation artifact and with reduced integral dose. Fourth, during an interventional procedure, limited projection views can be taken to generate full 3D representations of the vasculature with accurate determination of vessel lumen morphology to enable computer fluid dynamic (CFD) calculations which in turn can be used to plan further EIGI treatment within the patient treatment time. Finally, as EIGI procedures become more complex, the consequent patient dose especially where improved image quality is implemented must be more carefully monitored. For example, we found that patient dose actually increased for certain electro‐physiology (EP) procedures performed in our EP Lab following replacement of a mobile c‐arm with a fixed unit capable of generating improved image quality. In conclusion, while progress is being made toward fulfilling the predictions made by the authors in the Vision 2020 paper published early in 2008, EIGI remains open to continuing exciting advancements.

Educational Objectives:

1. Appreciate the progress being made in improved EIGI devices and imaging systems.

2. Understand the operation of new high‐resolution micro‐angiographic systems including the SSXII and the operation of dual‐detector ROI CB‐CT systems.

3. Understand the role of limited view acquisition for providing 3D images.

4. Appreciate the patient exposure burden during EIGI procedures.

[Supported in part by NIH Grants R01 EB002873, R01 NS43924, R01 EB00842501, R01 HL52567, UB Foundation IRDF, and an equipment grant from Toshiba Medical Systems Corp.].
TU‐D‐AUD B‐06: Quality Assurance (QA) and IGRT of Elekta XVI Cone Beam System for Clinical IMRT
Authors: Tsai J , Li S , Kuritzky N , Micaily B , Chan P , Miyamoto C
Published: July 2008

Purpose: To explore QA and IGRT of XVI cone beam CT (XVICBCT) system for multifarious IMRT with obscure and mobile target(s) to minimize toxicity to the patients. Method and Materials: Image quality (IQ) between XVICBCT and planning fan beams CT (TPFBCT), and XVICBCT IQ associated with gantry angular rotation were explored. IGRT functionality of XVICBCT was examined by humanoid pelvis (Rando) Phantom: an artificial target within the Phantom was tested and analyzed for coordinates shift consistency. Radiation exposure by XVICBCT was assessed with a Radcal ion chamber. To evaluate the advantage of XVICBCT for isodose distribution toward the target, a Jar Phantom containing a soap target and rice as tissue was provided. A film was inserted to the soap target center during IMRT +/− XVICBCT. Daily shifts from XVICBCT were recorded. Setup shift analyses of 30 prostate patients with average of 25 daily IGRT were attached. Results: IQ between XVICBCT/TPFBCT “normalizing” to soft‐tissue for head and neck and to bony‐tissue for prostate indicates TPFBCT has upper edge for tissue differentiation. XVICBCT is brighter than TPFBCT due to more scattering. Nevertheless, XVICBCT's complementary role as IGRT for IMRT is a contributive asset. XVICBCT radiation exposure measurement shows higher dose for smaller anatomy. Shifting verification of a movable target setup shows XVICBCT detected the coordinate's shifts in agreement with the expected (see Table‐1). The radiation distribution relative to the soap target for IMRT +/− IGRT of XVICBCT is convinced. Their Gaussian curve fittings of 30 prostate daily shiftings in X‐, Y‐, and Z‐ coordinates indicate the IMRT with XVICBCT are within sub‐millimeter. Conclusion: XVICBCT system is sufficient and accurate for image guided IMRT. Daily IGRT shift analysis demonstrates setup uncertainty is within mm providing conformity to the target(s).
TU‐D‐AUD B‐07: Feasibility Study for Linac‐Based Intensity Modulated Total Marrow Irradiation
Authors: Wilkie J , Tiryaki H , Smith B , Roeske J , Aydogan B
Published: July 2008

Purpose: Total body irradiation (TBI) is used in the pre‐conditioning regimen prior to bone marrow transplant for treatment of hematological malignancies. Intensity modulated total marrow irradiation (IMTMI) is proposed to reduce the large volumes of normal tissue irradiated during TBI, and thus the associated toxicities. The goal of this study was to assess the feasibility of a linac‐based IMTMI method. Method and Materials: The planning and delivery of linac‐based IMTMI was assessed using an anthropomorphic Rando phantom. A three‐isocenter technique was used to provide a full body plan with dynamic feathering at the edges of each isocenter plan. During treatment delivery, thermoluminescent dosimeters (TLDs) were placed at twenty two positions throughout the phantom to compare the delivered doses to the planned doses. Individual IMRT verification plans were also delivered to a solid water phantom for each isocenter, and doses measured from an ion chamber and film were compared to the planned doses. Results: The treatment plan indicated that target bone coverage was achieved with 98% of the volume receiving 99% of the prescription dose. Doses to critical structures were reduced by as much as 64% compared to conventional TBI. TLD readings demonstrated accurate dose delivery, with a mean point dose difference of 3% from the calculated value. Ion chamber readings for the verification plans were also within 3% of the expected doses and film measurements showed accurate dose distributions. Conclusion: The results of this study suggest that linac‐based IMTMI is feasible with delivered doses that compare favorably to planned doses. Moreover, our planning study indicates that IMTMI reduces the volume of normal tissue irradiated, and may lead to a decrease in treatment related sequelae. Conflict of Interest: Funding support provided by Varian Inc. (Palo Alto, CA) research fund.
TU‐D‐AUD C‐03: Liquid Scintillators for 2D Photon Dosimetry
Authors: Poenisch F , Archambault L , Briere T , Sahoo N , Beddar S , Mohan R , Gillin M
Published: July 2008

Purpose: Liquid scintillators have the potential of providing real‐time dosimetric information in 2D and even possibly in 3D. The purpose of this work is to study the performance of a liquid scintillator (LS) detector system for photon beam dosimetry. Method and Materials: The detector system consisted of a lucite tank (7×7×16 cm3), a camera objective and a cooled CCD type camera (Luca, Andor Technology, South Windsor, CT), which was shifted by 59 cm with respect to the center of the tank. The LS material BC‐531 (Saint‐Gobain, Newbury, OH) was used. The detector system was irradiated with 6‐MV photons on a Varian Clinac 21EX under standard conditions. Different field sizes, dose rates and camera light enhancement modes were measured and compared to the dose profiles of the treatment machine. Results: The light signal produced by the LS was slightly distorted by light scattering isotropically within the liquid and refraction at the tank interface. Taking into account this blurring we could reproduce the dose distribution. The LS material is nearly water equivalent. The detector system was also found to be dose rate independent. Using the electron magnification mode of the CCD camera we were also capable of measuring very low dose rates from an I‐125 seed. Conclusion: The present detector system is suitable for measuring 2D dose distributions under the conditions used in therapeutic photon treatments. Further investigations are underway to fully characterize this system to make it practical for routine clinical use.

Supported by the NCI (1R01CA120198‐01A2).
TU‐D‐332‐03: Quantifying Magnetic Moments of Small Spherical Objects in MRI Images
Authors: Hsieh C , Cheng Y , Haacke E , Neelavalli J
Published: July 2008

Purpose: The goal of this research is to develop a novel method for quantifying relative magnetic moment of any small object appearing in MRI images. This method may be useful in evaluating the magnetic characteristics of localized microbleeds in the brain or nanoparticles of contrast agents. We have successfully developed a 2D version applied only to long narrow cylindrical objects [1–2]. A key feature of this method is in the extraction of the desired information from MRI data without any a priori information. Method and Materials: The complex signal from a spherical object in a concentric spherical region is given in [3]. The signal contains three unknowns: effective proton density, volume of the object, and magnetic moment. The center of the object can be determined by minimizing the aggregate signal from the spherical region. The magnetic moment can be derived from the composite complex signals of three concentric spheres. Whether the object is paramagnetic or diamagnetic (relative to water) can be determined from the imaginary part of the complex signal. Both the thermal noise and the discrete voxels were included in simulations and were studied by the error propagation method. Results: The center of the spherical object was determined within 0.3 voxel from its true center. With a proper choice of the echo time, the magnetic moment of the object can be determined within 5% of the actual magnetic moment. This result has been confirmed by both simulations and error propagation analysis. Conclusion: Our preliminary study demonstrates the feasibility of the new method that can be used to accurately quantify the magnetic moment of a voxel wide object such as microbleeds or implanted nanoparticles without any a priori information.
TU‐D‐332‐08: Gd‐DTPA DCE‐MRI Assisted Image‐Guided PO2 Measurements in Rodent Tumor Xenografts
Authors: Huang M , Zhang M , Chang J , Le C , Zanzonico P , Humm J , Koutcher J , Ling C
Published: July 2008

Purpose: To optimize the correlation between interstitial pO2 readings and PET‐derived concentrations in tumors using co‐registered Gd‐DTPA DCE‐MRI to distinguish viable and necrotic tumor cells. Method and Materials: Nude rats with Dunning R3327‐AT xenografts were positioned in a custom‐fabricated mold and imaged by (1) T2‐weighted MRI imaging; (2) DCE‐MRI following IV injection of gadopentetate dimeglumine; (3) microPET for 1/2 hr post‐IV injection of or . The MRI and PET images were used to direct intra‐tumoral pO2 measurements using an image‐guided robot system. PET‐ and MRI‐visible fiducial markers were used to register the respective image and robot coordinate systems. pO2 was measured at 0.5‐mm increments along different tracks within the tumor using an OxyLite™ 4000 Oxygen probe advanced by the robot, providing point‐to‐point correspondence between the pO2 measurement and image‐voxel intensity. Measurement points in the necrotic region and those outside tumor region, identified by DCE‐MRI and T2‐weighted MRI, were excluded from the correlation analysis. Necrotic tissue was identified as having at t=2 min after contrast injection, where I0 and I(t) are MR image intensities before injection and at time t. Results: The registration error between images and the robot is <0.3mm. For three FMISO studies with 539 measurements and 21 tracks, the correlation between interstitial pO2 readings and intensities was not improved — vs . Four animals were studied using with 423 measurements and 20 tracks. The negative correlation improved significantly (p =0.00118) — vs — if only viable‐tumor points were considered. Conclusion: The negative correlation between voxel intensities and intra‐tumoral pO2 was improved when DCE‐MRI was used to exclude necrotic tissue pO2s. Exclusion of necrotic points did not improve the correlation for , however.
TU‐EE‐A2‐06: Are Dosimetric Guidelines of Adult Lung Cancer for Preventing Radiation Pneumonitis Applicable to Pediatric Radiotherapy Involving Lungs?
Authors: Hua C , Hoth K , Kun L , Krasin M
Published: July 2008

Purpose: Pediatric patients with Hodgkin's lymphoma and thoracic or paraspinal sarcomas who received radiotherapy may develop clinically significant radiation pneumonitis (RP) requiring the use of steroids. There are no dosimetric planning guidelines for pediatric lung to assess the likelihood of complication. We reviewed dose‐volume histograms (DVHs) and clinical complication data of 63 children treated on 2 prospective studies and evaluated the applicability of adult planning guidelines and risk models. Method and Materials: Forty children with Hodgkin's lymphoma and 23 with sarcoma receiving radiation to the thorax were studied. Patients with Hodgkin's lymphoma received 25.5 Gy involved‐field radiotherapy. Eight of which received 8 Gy to the entirety of one or both lungs through partial transmission blocks. Patients with sarcomas received 41.4–70.2 Gy conformal radiotherapy to the primary tumor. Clinical data on RP were collected from protocol databases and chart review with IRB approval. DVH parameters V13, V20, mean lung dose and normal tissue complication probability (NTCP) from adult lung models were calculated. Results: Four patients developed RP following radiotherapy. Two required the use of steroids (NCI CTC grade II). Of the 3 patients with Hodgkin's lymphoma who developed RP, 2 had received 8 Gy delivered to their entire right lung. Children with grade II RP have higher total lung DVHs, a V20 ⩾35% and mean lung dose above 16 Gy, consistent with the planning constraints set for adult lung cancer and Hodgkin's lymphoma. However, adult lung NTCP and risk models predicted low probability (0.2–0.3) for children who actually developed RP. Conclusion: The V20 and mean lung dose guidelines developed for adult lung cancer identify children at higher risk for RP. Better understanding of other clinical factors such as chemotherapeutic agents and individual sensitivity may be required to improve the predicability of NTCP models for children.
TU‐EE‐A3‐03: On‐Board Four‐Dimensional Digital Tomosynthesis (4D‐DTS): Optimization of Respiratory Motion Dependent Acquisition and Reconstruction Parameters
Authors: Maurer J , Godfrey D , Wang Z , Yin F
Published: July 2008

Purpose: Amplitude and period of respiratory motion vary among patients. For four‐dimensional digital tomosynthesis (4D‐DTS), the frequency of projection acquisition and the phase window must be optimized based on respiratory motion. The purpose of this study was to demonstrate optimization of these parameters. Method and Materials: Experiments were performed to demonstrate optimization of projection acquisition frequency and phase window based on respiratory motion characteristics. Projection images of a CIRS Dynamic Thorax Phantom were acquired using an on‐board imager (OBI) mounted on a clinical accelerator. The trajectory of a radiopaque marker attached to the phantom was monitored in projection space and used to assign phases to and sort projections for 4D‐DTS reconstructions. 4D‐DTS images were reconstructed for motion profiles ranging in superior‐inferior amplitude from 10–40‐mm and ranging in period from 3.5–7‐sec. DTS images for each profile were reconstructed from various sets of projections, simulating different projection acquisition frequencies and phase windows. Results: For a desired phase window, the frequency of projection acquisition must be optimized based on the respiratory period. If projections are acquired at too high of a frequency, many of the projections will not be used in the reconstructions, resulting in unnecessary imaging dose. If projections are acquired at too low of a frequency, 4D‐DTS images can be reconstructed with missing projections or with larger phase windows. The effect of reconstructing with missing projections is minor if the fraction of missing projections is small. As the number of missing projections increases, vertical streaking artifacts appear in the images. Conclusion: This work is part of a feasibility analysis for 4D‐DTS imaging. It establishes relationships between optimal projection acquisition frequency, phase window and respiratory motion characteristics. Projection acquisition frequency based on respiratory period was derived and demonstrated. Conflict of Interest: Research sponsored by Varian.