Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session H25: Focus Session: Medical Radiation Biology |
Hide Abstracts |
Sponsoring Units: DBP Chair: Paul Gueye, Hampton University Room: Colorado Convention Center 203 |
Tuesday, March 6, 2007 8:00AM - 8:36AM |
H25.00001: Proteomic determination of the biological sequelae of electron irradiation. Invited Speaker: Radiobiological-based treatment planning, where radiation dose is varied according to the regional biological variations in tumor tissue e.g. hypoxia, is becoming increasingly available and represents a radically different approach to improving the radiocurability of tumors. However, many of the current algorithms are based upon radiobiological phenomenon that have been studied for decades, e.g., the oxygen effect, and few utilize recent information on biological parameters that influence radiation response, e.g. EGFR status. With regard to electron treatment planning, there is a paucity of studies that have looked at the biological consequence of exposure to electrons of differing energies. The assumption is that there is a uniform cell killing per unit dose within the treatment volume. We have recently applied proteomic analysis to determine the impact that exposure to low and high-energy electrons have on the proteome of tumor cells; preliminary data suggests that a completely different spectrum of proteins are expressed 24 hours after exposure to 50 cGy of high versus low LET electrons. Changes in the cellular proteome provide an indication of the different cellular responses elicited in response to damage induced by high and low energy electrons. Should these protein changes reflect a different high versus low energy electron mediated cell inactivation, then algorithms may have to be developed that take into account the energy distribution within the dose field. A new technique called MALDI-imaging is capable of resolving proteomic differences at various sites in a tissue slice, thus allowing for a spatial determination of proteins within an irradiated tumor volume. In the future it may thus be feasible to determine the exact dose distribution with an irradiated field and determine the efficacy with which radiation kills tumor or normal cells. [Preview Abstract] |
Tuesday, March 6, 2007 8:36AM - 8:48AM |
H25.00002: Energy Spectra Reconstruction from Beta Emitters: A Study of the 90SR/90Y Case Ariano Munden, Paul Gueye, Cynthia Keppel, Chris Soares Reconstruction of individual electron energies from a 25$\mu $Ci $^{90}$Sr/$^{90}$Y radioactive source was performed using a dipole magnet and a scintillating fiber based detector. The dipole was constructed from two 5.08x5.08x2.54cm permanent magnets separated by a distance of 2 cm and having a maximum field of about 5kG. The electron beam leaving the source has a 2.28MeV maximum energy and was collimated within a 1cm at the entrance face of the magnet. Mapping of the magnetic field was done using a hall probe with an accuracy of about 2G. An electron detector consisted of blue shifted scintillating fibers with thicknesses of 1mm was used to detect the particles exiting the magnet. The data was compared with the ICRU energy distribution data for 90Sr, 90Y, and the composite 90Sr/90Y sources. The comparison was performed using a chi squared test. The setup provides an energy resolution less than 10{\%}. Such system could be used to reconstruct the energy distribution of any beta emitter for various types of calibrations as used in experimental physics (nuclear/high energy, medical, material sciences etc.). . [Preview Abstract] |
Tuesday, March 6, 2007 8:48AM - 9:00AM |
H25.00003: Validity Of the Low Energy Electromagnetic Physics As Implemented Using the Geant4 Toolkit Using A Sr$^{90}$/Y$^{90 }$Beta Emitter Source Rachel Black, Paul Gueye Calibration procedures in experimental physics (nuclear physics, material sciences, medical physics etc.) usually require the use of a low activity radioactive source. A model of the setup is most often performed to understand and optimize system performances. We have investigated the validity of the low energy electromagnetic physics models up to a 2.3 MeV as implemented in the Geant4 simulation toolkit. For this, a set of experiments was done using a beta emitter source consisting of a Sr$^{90}$/Y$^{90}$ in secular equilibrium. The electrons enter a permanent dipole magnet made of two 5.08x5.08x2.54 cm$^{3}$ blocks of Neodymium Iron Boron encased within an iron support frame and separated by a distance of 2cm. The measured Gaussian-like magnetic field separates the energies of the beta particles exiting the magnet. These electrons were then collected on an array made from sixteen 1mm thick scintillating fibers. The experimental data were compared against the ICRU database. The Geant4 simulation was developed to understand the energy loss and spectra obtained during the actual experiment. Forward (backward) simulation were done to generate (reconstruct) the (secondary) primary energy distribution of the source. Preliminary results of this study will be discussed. [Preview Abstract] |
Tuesday, March 6, 2007 9:00AM - 9:12AM |
H25.00004: Comparison of Fluid Attenuated Inversion Recovery Sequence with Spin Echo T$_{2}$ Weighted MRI for Characterization of Brain Pathology Indra Sahu, Sheshkant Aryal, Shanta Shrestha, Ram Ghimire, Keith Earle Twenty cases of different brain pathology have been studied via MRI using an open resistive magnet with magnetic field strength of 0.2 Tesla. The relative signal intensity with respect to the repetition time (TR) at fixed echo time (TE) 0.11 sec. has been studied. It was found that the signal intensity saturates for most lesions beyond a certain TR$\sim $6 sec in the T$_{2}$ - weighted image. The signal intensity differs with respect to the inversion time (TI) for fat and cerebrospinal fluid (CSF). It was found that the intensity is nulled for CSF at TI $\sim $1.5 sec. and for Fat at TI $\sim $ 0.10 sec in the FLAIR imaging sequence. Thus the intensity of the lesions is qualitatively different for the two sequences. From the radiological diagnostic point of view, it was concluded that the FLAIR sequence is more useful for the detection of lesions compared to T$_{2}$ sequences. [Preview Abstract] |
Tuesday, March 6, 2007 9:12AM - 9:24AM |
H25.00005: Experimental test of specific predictions of a model for the oscillatory response of p53 to DNA damage. Gustavo Stolovitzky, John Wagner, J. Jeremy Rice, Lan Ma, Wenwei Hu, Zhaohui Feng, Arnold Levine We have proposed a model for radiation-induced oscillations of the p53-mdm2 system that makes specific predictions about the range of both p53 and mdm2 transcription rates that support oscillation. Our model predicts that in cells with a polymorphism in the mdm2 gene (SNP309) that enhances mdm2 transcription levels, oscillations disappear. The kinetics of the p53 and Mdm2 levels measured in cells with different genotype at the SNP309 locus show that oscillations of p53 and Mdm2 are observed in the cells wild type for mdm2 SNP309 but not in cells homozygous for mdm2 SNP309. By using H1299 cell line expressing wild-type p53 under a tetracycline-regulated promoter we found that only when p53 levels are in a certain range, oscillation can be observed after stress. This study provides evidence that proper range of the p53 and Mdm2 levels are required for the coordinated p53-Mdm2 oscillation upon stress. [Preview Abstract] |
Tuesday, March 6, 2007 9:24AM - 9:36AM |
H25.00006: Impedance Analysis of Ovarian Cancer Cells upon Challenge with C-terminal Clostridium Perfringens Enterotoxin Geoffrey Gordon, Chun-Min Lo Both in vitro and animal studies in breast, prostate, and ovarian cancers have shown that clostridium perfringens enterotoxin (CPE), which binds to CLDN4, may have an important therapeutic benefit, as it is rapidly cytotoxic in tissues overexpressing CLDN4. This study sought to evaluate the ability of C-terminal clostridium perfringens enterotoxin (C-CPE), a CLDN4-targetting molecule, to disrupt tight junction barrier function. Electric cell-substrate impedance sensing (ECIS) was used to measure both junctional resistance and average cell-substrate separation of ovarian cancer cell lines after exposure to C-CPE. A total of 14 ovarian cancer cell lines were used, and included cell lines derived from serous, mucinous, and clear cells. Our results showed that junctional resistance increases as CLDN4 expression increases. In addition, C-CPE is non-cytotoxic in ovarian cancer cells expressing CLDN4. However, exposure to C-CPE results in a significant (p$<$0.05) dose- and CLDN4-dependent decrease in junctional resistance and an increase in cell-substrate separation. Treatment of ovarian cancer cell lines with C-CPE disrupts tight junction barrier function. [Preview Abstract] |
Tuesday, March 6, 2007 9:36AM - 10:12AM |
H25.00007: Understanding Radiotherapy-Induced Second Cancers Invited Speaker: There is increasing concern regarding radiation-related second-cancer risks in long-term radiotherapy survivors, and a corresponding need to be able to predict cancer risks at high radiation doses. While cancer risks at moderately low radiation doses are reasonably understood from A-bomb survivor studies, there is much more uncertainty at the high doses used in radiotherapy. It has generally been assumed that cancer induction decreases rapidly at high doses due to cell killing. However, most recent studies of radiation-induced second cancers in the lung and breast, covering a very wide range of doses, contradict this assumption. A likely resolution of this disagreement comes from considering cellular repopulation during and after radiation exposure. Repopulation / proliferation with a significant number radiation-induced pre-malignant cells, tends to counteract the effect of cell killing, and keeps the induced cancer risks higher at high doses. We describe and apply a biologically based, minimally parameterized model of dose-dependent cancer risks, incorporating carcinogenic effects, cell killing and, additionally, proliferation / repopulation effects. The situation is somewhat different for radiation-induced leukemia, as repopulation via the blood stream tends to be with cells that originated father away from the treatment volume than is the case for solid second cancers, thus containing a smaller proportion of radiation-damaged cells. The model predictions agree well with recent data on second cancer risks, both for radiation-induced solid cancers and for radiation-induced leukemias. Incorporating repopulation effects provides both a mechanistic understanding of cancer risks at high doses, as well as providing a practical methodology for predicting, and therefore potentially minimizing, cancer risks in organs exposed to high radiation doses during radiotherapy. [Preview Abstract] |
Tuesday, March 6, 2007 10:12AM - 10:24AM |
H25.00008: Photoelectric Effect, Bremsstrahlung, and Compton Effect Formulas Should Contain Rotational and Vibrational Energies Stewart Brekke The kinetic energy element in the Photoelectric Effect, Bremsstrahlung and Compton Effect formulas should also include besides the linear kinetic energy element rotational (spin) and vibrational kinetic energy elements. In the photoelectric effect the formula should be $[ h\nu = 1/2mv^2 + 1/2I\omega_r^2 + (n + 1/2)\hbar\omega_v + \phi]$ where $\omega_r$ is the rotational angular velocity and $\omega_v$ is the vibrational angular frequency. Similarly, in Bremsstrahlung the kinetic energy lost to photon creation at total braking shoudl be $[1/2mv^2 + 1/2I\omega_r^2 + (n +1/2)\hbar\omega_v =eV =h\nu_{max}]$. The resulting kinetic energy of a recoil particle in the Compton Effect should be $[1/2mv^2 + 1/2I\omega_r^2 + (n +1/2)\hbar\omega_v = (h\nu)\Delta\lambda/(\lambda +\Delta\lambda)]$. Also, in pair production and annhiliation the kinetic energies of the annhiliated pair and created pair should include the spin and vibrational energies. [Preview Abstract] |
Tuesday, March 6, 2007 10:24AM - 10:36AM |
H25.00009: Exploring the Role of Calcium in Cardiac Cell Dynamics Carolyn Berger, Salim Idriss, Ned Rouze, David Hall, Daniel Gauthier Bifurcations in the electrical response of cardiac tissue can destabilize spatio-temporal waves of electrochemical activity in the heart, leading to tachycardia or even fibrillation. Therefore, it is important to understand the mechanisms that cause instabilities in cardiac tissue.Traditionally, researchers have focused on understanding how the transmembrane voltage is altered in response to an increase in pacing rate, i.e. a shorter time interval between propagating electrochemical waves. However, the dynamics of the transmembrane voltage are coupled to the activity of several ions that traverse the membrane. Therefore, to fully understand the mechanisms that drive these bifurcations, we must include an investigation of the ionic behavior. We will present our recent investigation of the role of intracellular calcium in an experimental testbed of frog ventricle. Calcium and voltage are measured simultaneously, allowing for the previous research regarding voltage to guide our understanding of the calcium dynamics. [Preview Abstract] |
Tuesday, March 6, 2007 10:36AM - 10:48AM |
H25.00010: Biological Response of Cancer and Normal Cells on Irradiation from Electrons with Energies up to 200 keV. Yuriy Prilepskiy This paper presents continuation data of the series of experiments with the electron gun of the CEBAF machine at Jefferson Lab (Newport News, VA), which is capable of delivering electrons with energies up to 200 keV. This 1.5 GHz beam permits to generate cellular damage within minutes. We have performed irradiation of cancer and normal cells with different electron energies and currents to investigate cell biological responses. The biological response is measured through proteomics analysis before and after irradiation. The living cells are encased in special air containers allowing proper positioning in vacuum where the electrons are present. The containers receive the irradiation from the mono energetic electrons with energy up to 120 keV, resulting in an irradiation from both electrons and a small number of photons from the original beam passing through the thin container window. This window allows approximately half of the beam to come through. The study will permit to address the physical processes involved in the RBE and LET at a level that supersedes current data listed in the literature. We will discuss the experimental setup and the second stage of data collected with the new more developed system. This research is part of a global program to provide detailed information for the understanding of radiation based cancer treatments. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700