Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session U16: Focus Session: Medical Physics and Radiation Biology |
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Sponsoring Units: DBP Chair: Richard Britten, Eastern Virginia Medical School Room: Morial Convention Center 208 |
Thursday, March 13, 2008 8:00AM - 8:36AM |
U16.00001: Image-Guided Radiation Therapy: the potential for imaging science research to improve cancer treatment outcomes Invited Speaker: The role of medical imaging in the planning and delivery of radiation therapy (RT) is rapidly expanding. This is being driven by two developments: Image-guided radiation therapy (IGRT) and biological image-based planning (BIBP). IGRT is the systematic use of serial treatment-position imaging to improve geometric targeting accuracy and/or to refine target definition. The enabling technology is the integration of high-performance three-dimensional (3D) imaging systems, e.g., onboard kilovoltage x-ray cone-beam CT, into RT delivery systems. IGRT seeks to adapt the patient's treatment to weekly, daily, or even real-time changes in organ position and shape. BIBP uses non-anatomic imaging (PET, MR spectroscopy, functional MR, etc.) to visualize abnormal tissue biology (angiogenesis, proliferation, metabolism, etc.) leading to more accurate clinical target volume (CTV) delineation and more accurate targeting of high doses to tissue with the highest tumor cell burden. In both cases, the goal is to reduce both systematic and random tissue localization errors (2-5 mm for conventional RT) conformality so that planning target volume (PTV) margins (varying from 8 to 20 mm in conventional RT) used to ensure target volume coverage in the presence of geometric error, can be substantially reduced. Reduced PTV expansion allows more conformal treatment of the target volume, increased avoidance of normal tissue and potential for safe delivery of more aggressive dose regimens. This presentation will focus on the imaging science challenges posed by the IGRT and BIBP. These issues include: \textit{Development of robust and accurate nonrigid image-registration (NIR) tools:} Extracting locally nonlinear mappings that relate, voxel-by-voxel, one 3D anatomic representation of the patient to differently deformed anatomies acquired at different time points, is essential if IGRT is to move beyond simple translational treatment plan adaptations. NIR is needed to map segmented and labeled anatomy from the pretreatment planning images to each daily treatment position image and to deformably map delivered dose distributions computed on each time instance of deformed anatomy, back to the reference 3D anatomy. Because biological imaging must be performed offline, NIR is needed to deformably map these images onto CT images acquired during treatment. \textit{Reducing target and organ contouring errors}: As IGRT significantly reduces impact of differences between planning and treatment anatomy, RT targeting accuracy becomes increasingly dominated by the remaining systematic treatment-preparation errors, chiefly error in delineating the clinical target volume (CTV) and organs-at-risk. These delineation errors range from 1 mm to 5 mm. No single solution to this problem exists. For BIBP, a better understanding of tumor cell density vs. signal intensity is required. For anatomic CT imaging, improved image reconstruction techniques that improve contrast-to-noise ratio, reduce artifacts due to limited projection data, and incorporate prior information are promising. More sophisticated alternatives to the current concept fixed boundary anatomic structures are needed, e.g., probabilistic CTV representations that incorporate delineation uncertainties. \textit{Quantifying four-dimensional (4D) anatomy}: For adaptive treatment planning to produce an optimal time sequence of delivery parameters, a 4D anatomic representation, the spatial trajectory through time of each tissue voxel, is needed. One approach is to use sequences of deformation vector fields derived by non-rigidly registering each treatment image to the reference planning CT. One problem to be solved is prediction of future deformed anatomies from past behavior so that time delays inherent in any adaptive replanning feedback loop can be overcome. Another unsolved problem is quantification 4D anatomy uncertainties and how to incorporate such uncertainties into the treatment planning process to avoid geometric ``miss'' of the target tissue. [Preview Abstract] |
Thursday, March 13, 2008 8:36AM - 8:48AM |
U16.00002: Bridging the Gaps between IGRT Systems and R{\&}V Systems Yulong Yan, Xuejun Weng, Jose Penagaricano, Vaneerat Ratanatharathorn Image Guided Radiation Therapy (IGRT) is the next-generation of technology for high precision radiotherapy. BrainLAB ExacTrac and Tomotherapy are two of them. Unfortunately, neither of the two communicates with any Record and Verify (R{\&}V) system for seamless radiation therapy workflow. So two dedicated software systems, iPump and ScreenBee, have been developed respectively to bridge the gaps between IGRT systems and the R{\&}V systems to allow remote image reviewing as well as consolidation of patient's medical records. As an image pumping utility, iPump periodically searches for new registered images, fuses them and sends them to the R{\&}V system via DICOM connection. The built-in instant messaging mechanism automatically notifies the attending radiation oncologists right after images were sent. ScreenBee is a DICOM screen dumper. Instead of sending unsupported treatment parameters, it captures their graphical presentations on the computer screen and sends them to the R{\&}V system. Both iPump and ScreenBee have been extensively tested and evaluated in our clinic. They reduce the cost and improve the efficiency and the safety of clinical procedures. They also act as key integral components of our facility on its way toward the digital and paperless future. [Preview Abstract] |
Thursday, March 13, 2008 8:48AM - 9:00AM |
U16.00003: Hyperthermal heavy ion damage to DNA bases Sarvenaz Sarabipour, Zongwu Deng, Michael Huels Ionization and fragmentation of DNA is a key step in biological radiation damage. When heavy ions cross the cell, secondary ballistic ions, electrons and radicals are generated along the ion tracks. Here we report measurements of ionic fragments induced by 1-100eV Ar$^{+}$ irradiation of Adenine, Guanine and Cytosine films on Pt. Experiments are conducted with a UHV ion-beam apparatus consisting of a low energy ion source, a beam line with high resolution magnetic mass spectrometer (MS), a biomolecular film preparation system, and a reaction chamber with high-resolution quadrupole MS to monitor desorbing ion yields. Among the major fragments, NH$_{4}^{+}$ was identified in the desorption mass spectra of all bases examined, indicating efficient de-amination; in cells this results in pre-mutagenic lesions. Several important factors, e.g. intra/inter-molecular proton/hydrogen tunneling, tautomeric equilibrium and the molecular geometry of the bases in the films likely contribute to ion induced de-amination, and will be discussed here. [Preview Abstract] |
Thursday, March 13, 2008 9:00AM - 9:12AM |
U16.00004: Physical and Clinical Evaluation of Standardized Uptake Values Cristina Lois, Bjoern W. Jakoby, Karl Hubner, Mario Ca\~nadas, David W. Townsend The Standardized Uptake Value (SUV) is often used in positron emission tomography (PET) to differenciate malignant from benign tumors, and to monitor the progress of the patient response to therapy. Despite its name, SUV may depend on both PET scanner hardware and software details, and will depend on the imaging protocol. In this paper, we present a study of the SUV variability according to these external factors. To study the influence of the PET device, phantom studies were performed on two different combined PET/CT scanners. SUVs were obtained using several reconstruction algorithms and different reconstruction matrix sizes. To study the influence of the imaging protocol, patients were injected with 370 MBq of 18F-FDG and scanned at 60 and 90 min post-injection. SUVs were obtained applying several clinical image reconstruction algorithms. Significant differences in SUVs were obtained depending on the PET scanner, reconstruction method, and imaging protocol. It is essential, therefore, to follow a strict protocol in order to reliably compare FDG uptake with SUVs. Our results may have a significant clinical impact in order to provide an unbiased SUV thereshold to determine malignancy. [Preview Abstract] |
Thursday, March 13, 2008 9:12AM - 9:48AM |
U16.00005: The Dose Response Relationship for Radiation Carcinogenesis Invited Speaker: Recent surveys show that the collective population radiation dose from medical procedures in the U.S. has increased by 750{\%} in the past two decades. It would be impossible to imagine the practice of medicine today without diagnostic and therapeutic radiology, but nevertheless the widespread and rapidly increasing use of a modality which is a known human carcinogen is a cause for concern. To assess the magnitude of the problem it is necessary to establish the shape of the dose response relationship for radiation carcinogenesis. Information on radiation carcinogenesis comes from the A-bomb survivors, from occupationally exposed individuals and from radiotherapy patients. The A-bomb survivor data indicates a linear relationship between dose and the risk of solid cancers up to a dose of about 2.5 Sv. The lowest dose at which there is a significant excess cancer risk is debatable, but it would appear to be between 40 and 100 mSv. Data from the occupation exposure of nuclear workers shows an excess cancer risk at an average dose of 19.4 mSv. At the other end of the dose scale, data on second cancers in radiotherapy patients indicates that cancer risk does not continue to rise as a linear function of dose, but tends towards a plateau of 40 to 60 Gy, delivered in a fractionated regime. These data can be used to estimate the impact of diagnostic radiology at the low dose end of the dose response relationship, and the impact of new radiotherapy modalities at the high end of the dose response relationship. In the case of diagnostic radiology about 90{\%} of the collective population dose comes from procedures (principally CT scans) which involve doses at which there is credible evidence of an excess cancer incidence. While the risk to the individual is small and justified in a symptomatic patient, the same is not true of some screening procedures is asymptomatic individuals, and in any case the huge number of procedures must add up to a potential public health problem. In the case of radiation oncology, modern innovations such as Intensity Modulated Radiation Oncology or Proton Therapy both result in a substantial total-body dose to the patient, which must result in an increased incidence of second cancers. The technology exists to reduce these total body doses and the problem needs to be addressed. [Preview Abstract] |
Thursday, March 13, 2008 9:48AM - 10:24AM |
U16.00006: Panel Discussion on Medical Physics and Radiation Biology and pathways to these fields Invited Speaker: Medical Physics is one of the less know physics field but one that has the most impact on our daily life. It is intrinsically linked to radiation biology as the latter provides crucial inputs to the former including treatment planning software packages, understanding of cancer treatment optimization, etc. This panel discussion, composed of renown experts in these fields and who are part of the four medical physics sessions to be presented during this 2008 APS March meeting, will provide an environment for the audience to fully understand what medical physics and radiation biology are about and the various pathways to become a successful practitioner or researcher for contributing in these fields. [Preview Abstract] |
Thursday, March 13, 2008 10:24AM - 10:36AM |
U16.00007: Anomalous Effect of Surface Diffusion on NMR Signal in Restricted Geometry Neranjan Edirisinghe, Vadym Apalkov, Gennady Cymbalyuk The diffusion of magnetic molecules along the surface of restricted media and the coupling of the surface and the bulk translational motions can strongly modify the echo attenuation NMR signal in the pulse field gradient measurements. The origin of this strong effect is the change of the symmetry of the lowest diffusion eigenmode of the system. We illustrate the effect of surface diffusion for cylindrically symmetric system. We find the parameters of the system under which the anomalous behavior of echo signal can be observed. [Preview Abstract] |
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