bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐T‐617‐03: Dosimetry of Beta Emitting Intravascular Brachytherapy Sources
Authors: Treis S , DeWerd L , Micka J
Published: June 2005

Purpose: To verify the accuracy of current intravascular brachytherapy (IVBT) Sr‐90 calibration standards and to generate accurate and detailed IVBT beta dosimetry by analyzing dose distributions in a liquid water medium Method and Materials: High Sensitivity radiochromic film as well as lithium fluoride thermoluminescent dosimeter (TLD) 1×1×1mm microcubes were exposed in liquid water to a Novoste Beta‐Cath Sr‐90 IVBT source pellet. Calibration exposures were performed with a Tracerlab RA‐1 Sr‐90/Y‐90 ophthalmic applicator directly traceable to the National Institute of Standards and Technology (NIST) absorbed dose to water standard. Film and TLDs were read 24 hours post‐exposure using a Molecular Dynamics Personal Densitometer SI scanner (633nm HeNe laser light source) and a Harshaw 5500 unit, respectively. All exposures were made in a custom built water tank with computer controlled high precision Velmex tracks providing three axes for movement of measurement devices. Results: Preliminary radial depth dose measurement results with film and TLDs correspond within uncertainty estimates to data published by Soares et al, which is the current NIST standard for IVBT beta sources. The TLDs showed significant volume averaging over their 1mm thickness, requiring Monte Carlo correction to determine the effective point of measurement for each dosimeter. Conclusion: Liquid water measurements of IVBT beta dosimetry validate the results from previously published studies conducted solely in plastics and in air. These measurements also reduce experimental uncertainty by eliminating the conversion to water from data taken in water mimicking media.
WE‐C‐T‐617‐04: Absolute Calorimetric Calibration of I‐125 and Pd‐103 Brachytherapy Sources
Authors: Stump KE , DeWerd LA
Published: June 2005

Purpose: To develop an absolute method of low energy, photon‐emitting brachytherapy source strength specification that provides high precision and high accuracy measurements in terms of both the total contained and emitted power of the source. Method and Materials: A cryogenic calorimeter has been developed utilizing high temperature superconducting transition edge sensors as thermometers. The instrument is capable of providing direct measurements of the total source power as well as only the fraction that is emitted by the source. The calorimeter makes use of the well‐established electrical substitution principle to provide a direct measurement of power. With this method, a temperature control feedback loop is used to maintain a thermometer resistance set point in the center of the thermometers' superconducting transition. The heater power required to maintain this set point is compared both with and without the source present. The difference between the two heater powers is the measurement of source power. Results: Preliminary contained power measurements made with the calorimeter demonstrate a precision of approximately 0.5%. The power measurements are compared to air kerma strength measurements by means of Monte Carlo calculations. Using this method, agreement between the measurements is within 1.5%. The calorimeter has a demonstrated noise floor of 2 nW. Current work is focused upon evaluating an improved detector design and performing contained power and emitted power measurements of several different source types and strengths. Conclusion: The initial measurements with the calorimeter indicate that it is possible to provide high precision, high resolution power calibrations of brachytherapy sources. Features of this method are that no conversion factors are used to arrive at the desired quantity and few correction factors are required. Current work is focused upon evaluating an improved detector design and performing contained power and emitted power measurements of several different source types and strengths.
WE‐C‐T‐617‐06: Spectral Reconstruction by Scatter Analysis
Authors: Jalbout Wassim
Published: June 2005

Purpose: To reconstruct accelerator photon beam energy spectra by scatter analysis. Method and Materials: The method consists in irradiating a plastic phantom at standard 100cm SSD and inferring primary beam spectral information based on the measurement with a standard Farmer chamber of scatter around the phantom at several specific scatter angles: a scatter curve is measured which is characteristic of the primary spectrum at hand. A Monte Carlo code is used to simulate the scatter measurement setup and predict the relative magnitude of scatter measurements for mono‐energetic primary beams. Based on mono‐energetic primary scatter data, measured scatter curves are analyzed and the spectrum unfolded as the sum of mono‐energetic individual energy bins using the Schiff bremsstrahlung model. In comparison with spectral reconstruction by attenuation analysis, scatter is shown to be a measurable quantity that varies steeper with primary photon energy than attenuation does, providing the potential for a better resolving of adjacent energy bins within the spectrum. Results: The method is applied to an Elekta/SL18 6MV photon beam. The reconstructed spectrum matches the Monte Carlo calculated spectrum for the same beam within 6.2% (average error when spectra are compared bin by bin). Depth dose values calculated for the reconstructed spectrum agree with physically measured depth dose data to within 1%. Conclusion: The method has potential as a practical spectral reconstruction tool requiring few measurements under standard 100cm SSD and feasible in any radiotherapy department equipped with a conventional plastic scattering phantom and Farmer chamber.
WE‐C‐T‐6E‐03: Superparamagnetic Nanoparticles for Brain Tumor Diagnosis and Therapeutics
Authors: Zhang M
Published: June 2005

Gliomas are currently the most common and lethal type of primary brain tumor. Treating malignant gliomas remains a formidable challenge due to the difficulty in differentiating between tumor and healthy brain tissue, the rapid growth rate of invasive gliomas, intrinsic cellular resistance of gliomas to drugs, and the blood brain barrier (BBB) preventing the passage of drugs and contrast agents. My talk will describe our recent work in the development of a multifunctional nanoprobe for targeting glioma tumors by conjugating iron oxide nanoparticles with a glioma tumor targeting molecule and a near infrared fluorescing (NIRF) molecule. The nanoprobe is detectable by both magnetic resonance imaging and fluorescence microscopy, and exhibits significant targeting capability to glioma cells and effective inhibition to glioma cell migration. Our results demonstrate a cellular‐level resolution that may promise accurate delineation of otherwise poorly defined glioma interfaces resulting from their highly invasive morphology. The application of the nanoprobe for preoperative and postoperative diagnostic imaging with MRI and the real‐time intraoperative visualization of tumor margins with optical devices is a novel approach to improve the effectiveness of diagnostic and therapeutic modalities available for brain tumor patients.
WE‐D‐I‐6B‐03: The Role of Secondary Photons in the Quantum Absorption Efficiency of Megavoltage X‐Ray Detectors: Is Dmax the Ideal X‐Ray Converter Thickness?
Authors: Hajdok G , Battista J , Cunningham I
Published: June 2005

Purpose: To quantify the impact of x‐ray converter thickness and determine the role of secondary photons on the quantum absorption efficiency of megavoltage x‐ray detectors (metal plate/phosphor screen) used in portal imaging and megavoltage CT. Method and Materials: The Electron Gamma Shower (EGSnrc) Monte Carlo code was used to simulate the coupled photon‐electron transport within a copper (Cu) metal plate / gadolinium oxysulphide phosphor screen detector. The DOSRZnrc user code was used to score the spectrum of x‐ray energy deposition within the phosphor layer of the detector. In the simulations, a wide range of metal plate thicknesses (0–60 mm), phosphor screen thicknesses (0.1–5 mm), and incident photon energies (1–10 MeV) were investigated. The quantum absorption efficiency (QAE) was calculated from each absorbed energy distribution (AED) simulation. Results: Plots of QAE versus copper metal plate thickness indicate: the maximum QAE does not occur at the depth of maximum dose (dmax), but rather for a thicker metal plate; the metal plate thickness corresponding to maximum QAE increases with phosphor thickness; the magnitude of the QAE increases with phosphor thickness; and the maximum QAE is independent of the incident photon energy. For example, for a 1 MeV incident photon energy and 1 mm phosphor thickness, a factor of two improvement in the QAE can be achieved using a 12 mm thick metal plate. Conclusion: Our results suggest that using thicker metal plate converters can increase the QAE of megavoltage x‐ray detectors. This improvement in QAE can potentially lead to reductions in patient dose for megavoltage imaging. Furthermore, in terms of maximizing the QAE, higher order Compton scattered and pair annihilation photons that originate in the metal plate play a more important role than primary electrons.
WE‐D‐I‐6B‐04: Extracting CT Data in An Image‐Guided Radiotherapy Benchtop Where Continuous Radiation Contaminates Image Data
Authors: Shaw R , Kissick M , Mackie T , Jeraj R
Published: June 2005

Purpose: A subtraction technique is used to extract kilovoltage computed tomograpy (kVCT) image information from a data set that has the combined response from imaging and treatment radiations. This data acquisition problem addresses an imaging/radiotherapy system that has a source that cannot be pulsed, i.e. a radioactive source. Method and Materials: A benchtop image‐guided radiotherapy system uses a single CT detector and data acquisition system for imaging and treatment verification. The treatment radiation exposes every data collection cycle (DCC) and image radiation exposes every other DCC. Hence, sequential DCC alternates between the detector response from only the treatment radiation and the combined response from both the imaging and treatment radiations. To isolate the detector response from the imaging radiation, the image data set is produced from the subtraction of adjacent DCC. To demonstrate the effectiveness of this subtraction technique, CT images produced from this extracted data (extract‐CT) are compared to conventional kVCT images. Results: Images of simulated tissue equivalent cylinders from the extract‐CT and kVCT are similar. However, when comparing regions of uniformity, the standard deviation in pixel values are noticeably lower in kVCT. In extract‐CT, the standard deviation of pixel values in tissue equivalent trabecular bone, liver, breast, and adipose are respectively 7.1%, 5.3%, 31%, and 36% higher than kVCT. Conclusion: A dual‐source synchronization and data extraction method demonstrates that only a single detector and data acquisition system is required for a combined imaging/ radiotherapy system. The subtraction method presented in this work compensates for continuous radiation contamination of imaging data. However, the image quality is still compromised when compared to images without contamination. Conflict of Interest: This work was partially supported by grant from the NIH (PO1 CA088960) and a contract from TomoTherapy Inc.
WE‐D‐I‐6B‐06: Development and Analysis of a High Quantum Efficiency Thick Scintillator Based Video EPID for Sub‐MU Verification Imaging
Authors: Samant S , Gopal A
Published: June 2005

Purpose: The major limitation of current electronic portal imaging devices (EPIDs) is poor quantum efficiency (QE) with less than 5% of incident radiation being typically detected. We present a high QE prototype EPID based on a CsI(Tl) thick scintillation crystal (TSC) for high quality sub‐MU verification imaging. Method and Materials: The prototype TSC utilizes a 12 mm thick clear 17×17cm2 CsI(Tl) screen (QE=24%) coupled to a 12‐bit, 1024×1240 Plumbicon‐tube camera (250 μm pixel‐size at isocenter) installed on a clinical Siemens BEAMVIEWPLUS gantry. The initial performance of the TSC was studied with experimental measurements of spatial resolution and noise, along with a quantum accounting diagram (QAD) based on linear cascaded systems theory to predict system detective quantum efficiency (DQE). The theoretical model was used to study the effect of various components of the detector geometry on image quality, and to optimize the TSC for improved image quality. Results: The current TSC prototype with DQE(0)∼0.01 provides an order‐of‐magnitude improvement in image quality over traditional VEPIDs, while matching the performance of flat‐panel imagers at low frequencies. Since the optical geometry of the BEAMVIEW gantry was not optimized for the TSC, there was some loss in spatial resolution resulting in diminished performance at high frequency. Overall good image quality was observed even at low exposures. Conclusion: The enhanced luminescent output of the TSC results in high quality portal images even at sub‐MU dose, and significant potential for daily verification imaging without risk of additional patient dose and intra‐treatment imaging to monitor patient motion. Proposed improvements in the TSC include the optimization of the detector geometry for greater light collection efficiency and spatial resolution. Based on the QAD model, the performance of the TSC with proposed improvements is expected to improve significantly (DQE(0)∼0.1) and exceed that of current flat‐panels.
WE‐D‐I‐6B‐09: Tracking Prostate Motion and Isocenter Offset During Treatment Using the Calypos(tm) 4D Localization System
Authors: Willoughby T , Kupelian P , Litzenberg D , Sandler H , Levine L , Dimmer S
Published: June 2005

Purpose: To evaluate use of a real‐time tracking system to determine intrafraction prostate motion and isocenter offset. Method and Materials: Calypso® 4D Localization System (“Calypso System”, Calypso Medical, Seattle, WA) is a patient positioning device to be used as an adjunct for radiation therapy. Calypso System includes implanted markers (Beacon® transponders) and external electronics consisting of a movable console and electromagnetic array, user interface, infrared cameras, and tracking station. The external electronics continuously localize the implanted transponders using electromagnetic signals. Treatment target position offsets are computed based on transponder and isocenter coordinates from CT scans. In a pilot study at two centers, 11 patients were tracked during an 8‐minute session. In a follow‐on study at five centers, tracking data will be acquired during radiation delivery in 30 patients. Patients enrolled on study are seeking radiation therapy for prostate cancer and have three transponders implanted into the prostate gland. Patients are set to skin marks and then adjusted using the Calypso System for final alignment for radiation delivery. Organ motion and isocenter offset will be tracked during treatment. If the isocenter offset exceeds a user‐established limit during the fraction, the therapist will realign the patient using the Calypso System user interface. Results: Tracking sessions were performed on 11 patients to date. Two of the 11 patients showed significant organ motion (>1 cm) over an 8‐minute period. The longitudinal and vertical motion followed the same pattern of change, while no significant motion was detected in the lateral direction. The excursions persisted for over one minute. Conclusion: Tracking of the prostate showed significant motion over time periods of interest in radiation therapy in some patients. Tracking of organ motion has the potential to play an important role in IMRT and other conformal radiation treatments. Financial interest in Calypso Medical Technologies, Inc.
WE‐D‐I‐609‐03: Improving the Quantitative Accuracy of a Dedicated Small Animal SPECT/CT Scanner
Authors: Hwang A , Taylor C , Seo Y , Iwata K , Li J , Patt B , Hasegawa B
Published: June 2005

Purpose: High‐resolution radionuclide imaging is an important method for noninvasive assessments of small animal models of human disease. To improve the quantitative accuracy of small animal SPECT/CT, we have developed methods to calibrate the imaging geometry and energy response, and to perform attenuation correction. Method and Materials: All studies were performed using the X‐SPECT (Gamma Medica, Inc.), which consists of a compact scintillation camera and microCT system on a common gantry. Attenuation correction was performed developing a method to convert CT image values into attenuation coefficients by imaging a calibration phantom containing materials having known linear attenuation coefficients, and was assessed by acquiring SPECT images of phantom containing an aqueous solution of iodine‐125. The pinhole imaging geometry parameters were determined by scanning three point sources, and using a fitting algorithm to determine the values of the parameters. A pixel by pixel energy calibration was performed by acquiring data in list mode from flood phantoms. Results: CT calibration curves were obtained showing the correlation between CT image intensity and the linear attenuation coefficient for photons emitted by iodine‐125 and technetium‐99m. SPECT data reconstructed with attenuation correction improved uniformity, by eliminating the cupping artifact that otherwise decreases image intensity at the image center by 30%. The calibration for the imaging geometry resulted in a 10% change in image dimensions compared to images reconstructed using the nominal values for the geometric parameters. The energy calibration corrected for photopeak changes that varied as a function of spatial position and radionuclide photon energy, and produced images with improved uniformity. Conclusion: We are able to improve the quality and quantitative accuracy of SPECT images by applying improved image reconstruction and list mode processing techniques. Conflict of Interest: Bruce Hasegawa receives research support from Gamma Medica. Brad Patt, Joshua Li, and Koji Iwata are Gamma Medica employees.
WE‐D‐I‐609‐06: Comparison Between Two Small Animal Imaging CT Devices Used for Quantifying Lung Damage in Mice in Vivo
Authors: Cavanaugh D , Gladish G , Travis E , White R , Cody D
Published: June 2005

Purpose: Compare two x‐ray computed tomographic approaches to non‐invasively assess lung damage in mice: a commercially available micro‐CT and a prototype flat panel CT (fpCT) system. Method and Materials: The micro‐CT system requires respiratory gating, has a fixed tungsten anode x‐ray tube, and a CCD camera. A technique of 81 mA•sec at 80 kVp (0.16Gy) was utilized. The fpCT system accommodates a breath hold method, has a conventional CT x‐ray tube, and two CsI flat‐panel detectors. A technique of 800 mA•sec at 70 kVp (0.032Gy) with 200 μL of IV contrast was used. In this pilot investigation a subset of ten C57Bl/6 mice were analyzed; these mice received either 3 U/kg of Bleomycin to induce lung damage or saline for the control group by intratracheal administration. Both groups were serially scanned with both devices at baseline, 10, 14, and 21 days. Lung volumes at each time point were calculated using Analyze 5.0 for both the micro‐CT and fpCT image data sets. Results: Analysis of micro‐CT images resulted in smaller lung volumes than fpCT, most likely due to the gating procedure. Although the micro‐CT images exhibited more detail, the fpCT images had less noise and more tissue contrast within the lung regions, enabling easier detection of lung damage. The net decrease in measured lung volume due to damage accumulation over 21 days was 40 % from micro‐CT and 37 % from fpCT with respect to the average baseline lung volumes. Control mice lung volumes were stable to within 20% for both CT systems. Conclusion: The use of IV contrast with the fpCT system more than compensated for the reduced spatial resolution in this study. These mice survived multiple CT sessions even though lung damage was quickly accumulating in some cases. Additional data will be presented representing the complete study (n=19 mice).
WE‐D‐I‐609‐07: Analysis of Growth Dynamics of Treated Murine Liver Metastases Using Volumetric Ultrasound Micro‐Imaging
Authors: Wirtzfeld LA , Graham KC , MacKenzie LT , Postenka CO , Groom AC , MacDonald IC , Fenster A , Chambers AF , Lacefield JC
Published: June 2005

Purpose: Two methods were compared for analyzing therapeutic responses in an experimental murine liver metastasis model using longitudinal high‐frequency three‐dimensional (3D) ultrasound imaging. Method and Materials: B16F1 mouse melanoma cells were injected into the mesenteric vein of C57BL/6 mice to produce liver metastases. Treated mice received doxorubicin every second day starting seven days post injection and continuing until day 17. Untreated mice received saline injections on the same schedule. Imaging began eight days post injection and was performed every one to two days until day 19. Three‐dimensional images were acquired using a VisualSonics Vevo 660 ultrasound system with a 40 MHz transducer. Metastasis volumes were measured in 3D images by manual segmentation. Two growth curves were constructed for each metastasis by computing least‐squares fits of an exponential function and a Gompertz function, which is an exponential with a time‐varying rate parameter, to the volume data. Results: Eight untreated and 24 treated metastases were monitored. A significant (p < 0.05 in Wilcoxon rank‐sum tests) difference in untreated and treated tumor volumes was observed as early as day 12. The growth of untreated metastases was described equally well by exponential (mean ± standard deviation of ) or Gompertz functions. However, Gompertz functions modeled the growth of treated metastases more precisely than exponential functions . The difference between exponential and Gompertz r2 values for treated growth curves was significant (p = 0.040). Conclusion: High‐frequency 3D ultrasound imaging is sensitive to changes in murine liver metastasis growth rate produced by a chemotherapeutic agent, and may be capable of characterizing temporal variations in the growth rates of treated tumors. Conflict of Interest: VisualSonics has licensed 3D reconstruction, visualization, and segmentation software from our laboratory.
WE‐D‐I‐611‐01: The Science of Image Quality: Early Concepts, Maturing Ideas, and New Research Problems
Authors: Cunningham I
Published: June 2005

Our understanding of what determines image quality in medical imaging has evolved from the early radical ideas of Albert Rose in 1948 to modern task‐dependent signal‐detection theory. In between, many concepts such as the noise‐equivalent quanta and detective quantum efficiency have moved from being novel approaches to mainstream metrics with international standards in both academic and industrial laboratories. This presentation will provide a brief historical description of how these concepts evolved and how they are used at present. While they have proved very useful, all Fourier‐based metrics must be interpreted carefully when used to describe new digital technologies. Both the strengths and limitations of these methods will be summarized with an emphasis on some problems currently being investigated.
WE‐D‐I‐611‐03: Non‐Fourier Concepts in Image Quality
Authors: Myers K , Gagne R , Badano A , Gallas B , Kyprianou I
Published: June 2005

Medical images are acquired for the purpose of gathering information regarding the disease state of a patient. The quality of the image should be a measure of how a specified task may be performed given the resulting image. Image quality is task dependent; one imaging system may provide images that allow better task performance than another system's for one task, but worse for another task. Determining the quality of an imaging system involves specifying the task of interest, the range of objects that will be imaged, and the observer (human or machine reader) who will perform the task. In radiography it has become common to use Fourier measures to describe image quality through a combination of Fourier‐based measures of system resolution and noise. The Line Spread Function, when Fourier transformed, yields the Modulation Transfer Function (MTF) as a measure of system resolution. Use of the MTF to describe a system's resolution is appropriate when the imaging system is shift‐invariant, that is, the line spread function is independent of position. Image noise is described in the Fourier domain by the Noise Power Spectrum (NPS). We can use the NPS to describe the noise in an imaging system whenever the noise properties are stationary, meaning that the variance and correlations between fluctuations in different locations are not dependent on their absolute location. These Fourier measures of system resolution and noise are commonly combined to give an overall figure of merit known as the Detective Quantum Efficiency (DQE). The DQE describes the signal‐to‐noise transfer characteristics of an imaging system as long as those assumptions of shift‐invariance and noise stationarity are valid. In digital systems the image of an object is affected by the location of the object with respect to the pixel grid. In other words, the detector pixels cause the system to be shift‐variant. In this case the MTF does not describe the resolution properties completely. This is particularly the case for tomographic systems, where the point‐response function is quite position‐dependent. Moreover, in real imaging systems the noise properties will depend on position, most notably because real patients always have structure. So, the Fourier‐domain noise concept of Noise Power Spectrum does not capture all the properties of noise for real imaging systems and tasks. In this talk we will consider a general treatment of the imaging system as a mapping of information from the patient to the data, without the assumptions inherent in Fourier analysis. We will discuss approaches to the characterization of system resolution and noise in terms of position‐dependent parameters. Once such position‐dependent imaging properties of a system are determined, we can use them to calculate measures of image quality that summarize the usefulness of the images for the performance of various visual tasks.
WE‐D‐T‐617‐01: Characterization of a New 3D Dosimetric Material “PRESAGE” TM
Authors: Guo P , Adamovics J , Oldham M
Published: June 2005

Purpose: A pressing goal of modern radiation dosimetry is the development of effective and convenient three‐dimensional (3D) dosimetry systems that can measure and verify complex dose distributions. 3D dosimetry materials do exist but improvements would be valuable especially with regards to stability, uniformity, ease of handling and re‐usability. In this work we investigate and characterize the dosimetric properties of a promising novel material PRESAGE™. Method and Materials: A series of experiments were conducted to investigate the dose response, linearity, stability, reproducibility and dose rate dependency of PRESAGE™. To facilitate efficient evaluation of a wide range of parameters the experiments were performed on small samples of PRESAGE™ contained in optical cuvettes (1cm×1cm×5cm). A laser scanning system was developed that enabled pre‐and post irradiation scanning of the profile of optical‐density with depth along the central path of individual cuvettes at 633 nm. Cuvettes were also scanned in a spectrophotometer to detect spectral absorption. Results: The PRESAGE™ was found to be robust in regards to handling and exposure to laboratory environment. Linear relationship of optical response with dose was observed (within 3%) in cuvettes that had been handled and exposed to lab environment for significant periods. Good stability of optical contrast was observed up to 13 days post irradiation and the optical response had little dependency (within 3%) on dose rate. The dose response is significantly less than that observed with polymer gel dosimeters but PRESAGE™ formulations with enhanced sensitivity (0.16Gy/cm) have not yet been fully characterized. Conclusion: These evaluations of small samples of PRESAGE™ indicate a dosimeter that is highly practical and with good dosimetric properties. Of particular importance is PRESAGE's robustness in terms of exposure to air and materials, high stability of response with time post irradiation, and its high optical clarity.
WE‐D‐T‐617‐03: Characterization of a Novel Diamond Detector
Authors: Rodriguez M , DeWerd L , Griffin S , Schmidt D , Patel N , Jeraj R
Published: June 2005

Purpose: Test a novel diamond detector performance and applicability for radiation dosimetry. Detector sensitivity, stability and dependence on bias voltage, dose rate, energy and hardening have been studied. Method and Material: Detector was irradiated in a mini‐phantom. A modified electrometer and an external high power supply were used to collect the charge generated at the sensitive volume of the detector. Readings in the electrometer were collected by a computer via a hyperterminal connection at a rate of 10 values per second. Beam parameters SDD=100 cm, 10×10 cm2 field size were used. Dose rate was varied by altering the SDD. Results: Optimal charge collection stability was observed after a short pre‐irradiation and at +100 V bias. External bias voltages up to 225 V applied to the detector resulted in proportional charge collection rates. Signal is proportional to dose rate. No substantial variation in charge collection was observed when the detector was hardened to 10 kGy. Conclusion: The tested diamond detector has most of the characteristics needed for radiation dosimetry. Its performance is stable and the uncertainties in the charge collection will not affect the calculation of parameters in dosimetry. Therefore, this novel diamond detector is suitable for clinical use. Conflict of Interest: Research was supported in part by Standard Imaging Inc.
WE‐D‐T‐617‐06: Development of a Sealed Water Calorimeter for Clinical Electron Beams
Authors: Stewart K , Klassen N , Ross C , Seuntjens J
Published: June 2005

Purpose: The purpose of this project is to develop a water calorimeter for use in clinical electron beams to directly determine absorbed dose to water. This work presents the design of the Electron Sealed Water (ESW) calorimeter, preliminary measurements and evaluation of correction factors. Method and Materials: The calorimeter contains a 30 × 30 × 20 cm3 water phantom surrounded by a cooling system to allow for operation at 4°C. Two thermistor probes measure the temperature change inside a glass vessel filled with high‐purity nitrogen‐saturated water. Correction factors for the glass perturbation were calculated using Monte‐Carlo simulations. Corrections for thermal conduction were simulated using Femlab finite element modeling software. Resistance of the thermistor probes was measured using a lock‐in amplifier and an AC bridge circuit. Measurements were done for 6, 9, 12, 16 and 20 MeV electron beams from a Varian Clinac 21EX with a 10 × 10 cm2 applicator at 105.5 cm SSD with the thermistor probes positioned at dref. Irradiations of 667 MU were done at 1000 MU/min for an irradiation time of 40 s. Measurements were also taken with a PTW Roos ion chamber inside the calorimeter phantom. Results: The standard error on the mean temperature change for each energy was less than 0.2%. Reproducibility for measurements on separate occasions was 0.2%. When normalized to the 12 MeV measurements, values of k'R‐50 for the Roos chamber calculated from calorimeter measurements for the 9, 16 and 20 MeV beams and agreed with TG‐51 values within 0.7 %. Conclusion: Water calorimetry in electron beams has previously been regarded as unfeasible as high gradients were thought to provoke unmanageable temperature gradients. Using the ESW calorimeter, we have shown for the first time that reproducible measurements can be performed in electron beams with energies as low as 6 MeV.
WE‐D‐T‐6E‐01: A New Lung IMRT Planning Algorithm with Dose Shaping Strategy to Compensate for Respiratory Motion
Authors: Li X , Zhang P , Helminen H , Mah D , Kutcher G
Published: June 2005

Purpose: To develop a new lung IMRT planning algorithm that shapes dose distributions to the probability distribution of the tumor over the breathing cycle in order to compensate for respiratory motion, thereby enabling tumor dose escalation. Method and Materials: We implemented a new optimization algorithm on an in‐house IMRT planning system on an Eclipse (r) workstation (Varian, Palo Alto). Our new dose shaping algorithm makes the dose of each voxel on the 3‐D dataset proportional to its probability of being inside the tumor over the respiratory cycle. The maximum dose is set to be the prescription dose multiplied by the ratio of the volume encompassed by the extreme positions of the tumor to the tumor volume. We also implemented two other popular approaches: (1) an optimal margin method in which the margin is generated based on the extreme positions of the tumor; and (2) a convolution method that performs 4‐D dose calculations using a modeled tumor motion probability density function. A simulated 4‐D CT dataset, which was generated by superimposing the patient's respiratory motion pattern onto one's 3‐D CT dataset, was used to evaluate the performance of these three approaches via DVH comparison for the inhale phase of the breathing. Results: Five‐field 6MV beams were used for all plans delivering a total dose of 63Gy in 35 fractions. Comparing to the IMRT plan with optimal margin, the convolution method reduced the mean dose to the ipsilateral lung by 5% while maintaining the same tumor coverage. Compared to the convolution method, our dose shaping method achieved the same lung sparing, but is much faster and has the extra ability to escalate tumor dose: 95% tumor received more than 72Gy. Conclusion: Dose shaping method is able to spare the healthy lung tissue, and has the capacity to further facilitate dose escalation.
WE‐D‐T‐6E‐05: Geometrically Assisted Selection of Optimum Beams in IMRT Planning by Techniques of Computer Vision
Authors: Llacer J , Agazaryan N , Solberg T , Promberger C
Published: June 2005

Purpose: To define optimum beam orientations in IMRT by geometric analysis of the PTV and OARs using techniques of computer vision. The method is particularly applicable to situations when one or more OARs are adjacent to the PTV and where non‐coplanar beam orientations are employed, but can be used in cases requiring coplanar beams. The selected beam orientations are those that can most effectively yield desirable dose distributions in the PTV, sparing to a maximum extent adjacent OARs. Method and Materials: For each voxel of a PTV‐OAR interface, Gaussian Invariant techniques are used to obtain the two orthogonal components of a vector that defines a tangent plane. A two‐dimensional histogram of the number of voxels having specific values of those two vector components is formed. Clusters or peaks in the histogram correspond to dominant plane orientations in the interface. Considering the anatomy of a patient whose PTV and OARs have been projected on the surface of a hemisphere, each histogram cluster gives rise to an arc on that surface. Any beam oriented from a point in that arc towards the isocenter is then a possible optimum beam. At the present stage of development, the planner selects one or more optimum orientations for each OAR by using beam's‐eye‐view (BEV) tools. Results: Initial application of the method to clinical cases yields optimizations that are consistent with current clinical practice, with the geometrically assisted definition of optimal beams taking a small fraction of the time usually needed for that task. Conclusion: The work presented can be the basis of a nearly full automatic method of optimal beam orientation selection in which dominant arcs on the hemispheric surface are found by a self‐organizing network and the subsequent BEV analyses are carried out automatically by a rule based system.
WE‐D‐T‐6E‐07: Incorporating Clinical Outcome Data Into IMRT Inverse Planning
Authors: Xing L , Yang Y , Widrow B
Published: June 2005

Purpose: To develop a biologically more sensible yet clinically practical framework for IMRT planning by incorporation of existing clinical endpoint data. Method and Materials: To effectively integrate outcome data into inverse planning, two critical steps are (i) identifying the variable that characterizes the dose‐volume status of an organ; and (ii) writing the objective function as a function of the variable with consideration of outcome data. The concept of effective volume is extended to the voxel domain for this purpose. For a dose‐volume structure, the objective function depends not only the dose, but also its volumetric status. When compared with conventional quadratic function, the effect of the new scheme is to modulate the penalty distribution by applying more penalties on those high‐dose voxels, and vice versa. The modulation is organ dependent and determined by the clinical outcome data. An iterative algorithm is used to optimize the system. The new formalism is applied to plan a head‐and‐neck case and a prostate case. The results are compared with that obtained using the quadratic objective function with DVH constraints. Results: The technique provides clinically sensible ranking of competing IMRT plans. For parotid glands, for example, it yields the same score when the glands are irradiated 15Gy to 67%, or 30Gy to 30%, or 45Gy to 24% of the volume since they lead to the same outcome. On the contrary, the quadratic function yields different rankings for the three scenarios. Comparison with conventional technique indicated that, for the same target coverage, critical structure sparing is substantially improved for both cases. Conclusion: A new penalty scheme, in which the voxels are penalized differentially according to clinical outcome data, is proposed. The sub‐optimal performance of the current dose‐based inverse planning can be substantially improved by considering outcome data.
WE‐E‐E‐611‐02: Where Are We?
Authors: Ritenour E , Hendee W , Heintz P
Published: June 2005

A survey regarding the perceived quality of physics instruction of radiology residents was sent to all radiology programs in 2004. An identical survey was sent to program directors and chief residents. The Presidents of the American Association of Academic Chief Residents in Radiology and of the Association of Program Directors wrote cover letters to accompany the surveys, encouraging the expression of frank opinions in this anonymous survey. This presentation will present the results of the survey and will provide some opinions concerning the meaning of the results. Discussion will include information regarding some recent decisions by the American Board of Radiology as to changes in the grading of the physics exam for residents.
MO‐A‐I‐617‐01: PET Systems: Instrumentation and Data Acquisition
Authors: Fahey F
Published: June 2005

Positron emission tomography or PET is now considered one of the most important clinical imaging modalities, particularly in the fields of oncology and neurology. In addition, the application of PET to cardiology is swiftly growing. This presentation will discuss the instrumentation as well as the data acquisition associated with state‐of‐the‐art PET systems including PET‐CT. This talk will review the basics of positron emission, annihilation coincidence detection and instrumentation design. It will review detector designs in state‐of‐the‐art PET systems including the choice of detector materials. We will also describe both 2D and 3D PET data acquisition modes and the merits of each. We will discuss random coincidences, scatter and attenuation correction and current approaches being used to correct for these. For attenuation correction, calculated methods, measured methods using rotating rod sources as well as the use of CT will be discussed. At the end of this presentation, the participants will be able to:

1. list 3 detector materials routinely used in PET and at least one advantage or disadvantage of each,

2. describe the difference between 2D and 3D PET data acquisition.

3. discuss 3 current methods of attenuation correction used in PET and
MO‐B‐I‐617‐01: MR Accreditation Program Quality Control — Beyond Just the Scans and Measurements
Authors: Keener C
Published: June 2005

In recent years, the American College of Radiology (ACR) MR Accreditation Program (MRAP) has been adopted by more than 3000 facilities. Those sites agree to follow a quality control program set up and monitored by the medical physicist or MR scientist. They also agree to undergo initial and annual equipment evaluations by the medical physicist / MR scientist. There are several published documents, including the ACR Phantom Test Guidance and the 2001 ACR MR QC Manual, which describe required phantom tests and performance criteria. While helpful in assisting sites with the submission of phantom images for accreditation, these documents allow great discretion to the medical physicist in setting up the QC program without providing similar guidance in troubleshooting problems for a wide variety of scanners. A consulting medical physicist may see a wide variety of scanners, each for a short period of time, and needs to be able to provide the site with useful recommendations beyond the pass/fail status of the phantom tests. The physicist must gather this information from existing QC data and tests performed with the ACR and other readily‐available phantoms. This lecture will describe additional information which can be gathered from those data to produce recommendations for improving MR image quality.

Educational Objectives:

1. Understand basic MR QC tests using the ACR and on‐site phantoms and how the results of those tests can be combined and analyzed to troubleshoot problems.

2. Understand how QC test availability and results may vary depending on scanner manufacturer.

3. Understand how technologist QC data may be analyzed to troubleshoot QC problems.
MO‐B‐I‐609‐01: Ultrasound Probe Testing in Clinical Ultrasound QA Programs
Authors: Boote E , Moore W
Published: June 2005

Purpose: Tissue mimicking phantoms have been the primary tools employed by physicists for Ultrasound equipment acceptance and quality control programs. Recently, a new device has become commercially available that allows physicists, clinical engineers and service personnel the ability to ascertain the level of performance for ultrasound probes, based upon interrogation of individual elements. This provides an additional tool for the physicist to use in evaluating the performance of ultrasound equipment. Course Description: The first part of this course will discuss probe testing. Why probe testing is important and the ways in which defects in probes may affect ultrasound image quality. The device and how the results of the test can be interpreted will be presented. The second part of the course will present the use of this device as part of a clinical quality control program. This will include the use of phantoms and the device in an integrated fashion to provide valid acceptance testing and ongoing verification of system performance.

Educational Objectives:

1. The impact of transducer probe defects on image quality and Doppler ultrasound

2. How testing of individual probes elements can be performed

3. Interpretation of test results for probes

4. How to set up a program of Ultrasound QA/QC using phantoms and probe testing devices

Conflict of Interest: Wayne Moore is employed by Sonora Medical.
MO‐C‐T‐6E‐05: Early History of Radiation Physics
Authors: Almond P
Published: June 2005

In 1905, Einstein's annus mirabilis, Dr. Charles Lester Leonard began his presidential address to the American Roentgen Ray Society with, “A review of what has been accomplished in the decade since Roentgen's discovery is a fitting subject for the annual address in this decimal year…. It will form a base from which we can attempt to look into the future.” I wonder if Dr. Leonard would recognize the future if he could be present at this meeting, a century later, and see what it became. In the decade between the discovery of X‐rays by Roentgen in 1895 and Dr. Leonard's address much had happened in the world of radiation physics. Although there were new discoveries, especially that of radioactivity, the overall emphasis was upon the application of “radiation” to clinical problems without fully understanding the nature of the “radiation” or its interaction with matter, especially tissue. When Roentgen discovered X‐rays in November 1895, the news spread rapidly through the continental Europe, Great Britain and the United States and many individuals began generating and using them. This was not surprising since the basic equipment was readily available, Crooks tubes, high voltage generators, induction coils, etc, especially in academic departments and the information in newspaper accounts of Roentgen's work was detailed enough to get started. Physicists were just as likely therefore to be involved as medical doctors. Unfortunately the above equipment, except for the Crook's tube, was also being used for what became called electro‐therapeutics, the treatment of disease by electricity which on the whole was considered “quackery”. In the fall‐out between radiology and electro‐therapeutics the physicists became caught in the middle. This created problems for medical physicist that would take half a century to start addressing. No such problem existed in Great Britain allowing medical physics to develop earlier there than in the United States. Much of the development in the period 1985 to 1905 was in the area of X‐rays, although radium had been discovered by the Curies in 1898 it was very expensive, in 1906 1 gram of radium cost $50,000, and demand far exceeded supply. However the clinical application of radium was clearly recognized and programs for its therapeutic use in the treatment of cancer had started at a number of institutions world‐ wide. The major needs in 1905 were the requirement for the standardization of treatments, accurate measurement of radiation, reliable equipment and steady output, an understanding of the radiobiological effects of radiation, a basic understanding of the physics involved. In the next few years all of these questions would be extensively addressed.

Educational Objectives:

1. To appreciate the status of clinical radiation physics in 1905.

2. To realize what was and what was not known about radiation physics in 1905

3. To appreciate the problems that still had to be addressed.