bluuebunny/crossref_metadata_2025 huggingface dataset:
TU‐B‐ValA‐01: Digital Fluoroscopic Imaging: Acquisition, Processing and Display
Authors: Belanger B
Published: July 2006

The modern digital fluoroscopic imaging system has evolved to levels of complexity and automation that, when properly applied, can provide enhanced clinical performance and flexibility over a wide range of clinical applications in a user‐friendly manner. However, achieving maximum performance from such complex systems may be best achieved through cooperative efforts between manufacturers and clinical users, in which the well‐informed clinical team can utilize the degrees of freedom available in these systems to achieve the best clinical results for each medical application of interest. The medical physicist plays an important role in this process as the person who understands the relationships between physical imaging parameters, dose, and clinical imaging performance. Therefore, an understanding of system architectures, design philosophies, image processing capabilities, and degrees of freedom in procedure programming allow the medical physicist to play a more effective role. To this end, an overview of modern digital fluoroscopic imaging system will be presented, with particular attention given to the range of fluoroscopic and record imaging modes provided, automatic exposure control systems, common image processing algorithms, and procedure protocol selections. Recommendations for minimizing pitfalls in equipment testing will also be presented, along with some of the unique considerations for flat panel detectors versus image intensifier‐based imaging systems.

Research sponsored by GE Healthcare.

Educational Objectives:

1. Understand the architecture of modern fluoroscopic systems, including major image and data communication pathways, control systems, and image processing from acquisition to display.

2. Gain familiarity with the flexibility in control and processing afforded by new technologies and architectures, and how manufacturers use these.

3. Be aware of the various fluoroscopic imaging modes and the related image quality and dose considerations, including dose monitoring and reporting.

4. Understand common image processing techniques, such as edge enhancement, multiband filtering, and temporal filtering, and their impact on image quality.

5. Recognize the unique aspects of Digital Flat Panel Detectors and the related implications for fluoroscopic system behavior and performance.

6. Be able to identify the types of automation implemented in systems, and know how to avoid related pitfalls in testing.

7. Recognize the various procedure protocol programming capabilities available, and how they may be customized to meet clinical objectives.
TU‐C‐330A‐06: Evaluation of Internal Lung Motion Based On Extended Time Ultra‐Fast MRI Scan
Authors: Cai J , Sheng K , Read P , Molloy J , Altes T , Brookeman J
Published: July 2006

Purpose: In order to develop radiation treatment planning based on a displacement probability function for lung tumors we developed a dynamic MRI protocol to image the internal human respiratory lung motion during a several minute period that simulates the duration of a radiation treatment, evaluated the long time displacement probability distribution function (PDF) of pulmonary vessels as surrogate tumors, and assessed its reproducibility with repeat imaging. Methods and Materials: TrueFISP (fast imaging with steady‐state precession) sequence was adapted to acquire real time MR images of human lungs during 5 minute scans in both sagittal and coronal planes. A total of 26 pulmonary vessels from different regions (upper, middle and lower) in 3 healthy subjects were examined. Motion profile and displacement PDF of each tracked pulmonary vessel were evaluated. Experiments were repeated after 2‐3 weeks to test the reproducibility. Results: Motion profiles and displacement PDF of the same subject showed similarity, but great variation between different subjects. Displacement PDFs varied tremendously but tended to stabilize during the 5‐minute scan, and were reproduced reasonably well to various degrees in the repeated experiments after a subject specific stabilizing time (270s, 120s, 200s for Subject 1, 2, 3 respectively). Conclusions: Experiments for the first time using ultra‐fast real time MRI in extended time scans produce stable and reproducible displacement PDF of internal pulmonary structures, weakly depending upon different individual breathing patterns. This methodology is being investigated in a clinical trial at our institution to determine in a larger scale whether the reproducibility of motion is statistically significant and whether patients with lung tumor exhibit similar predictable breathing characteristics.
TU‐C‐330A‐07: Magnetic Resonance Electrical Impedance Mammography: A Feasibility Study
Authors: Kovalchuk N , Kallergi M , Wollin E , Heine J , Manohar A , Rabson D
Published: July 2006

Purpose: To demonstrate the feasibility of a new imaging technique consisting in simultaneous Magnetic Resonance Mammography and Electrical Impedance Scanning of the breast which does not require theoretically fat suppression and injection of paramagnetic contrast agents. Method and Materials: A theoretical formulation of the expected signal was developed and verified by the computer simulation demonstrating the distortion of the magnetic field caused by the injected currents. Two conducting breast phantoms were designed using breast tissue and tumor equivalent materials: (a) a soap phantom with a soap and salt solution as a cancer surrogate and (b) an agar phantom with a piece of fat‐free hotdog as a cancer surrogate. The stabilization paddles in a Symphony Breast Biopsy Array were modified to include Faraday shield electrodes fed by a variable frequency power source. The phantoms were placed between the modified paddles and imaged with a Siemens Magnetom Symphony Maestro Class 1.5 Tesla system with the current densities reaching 4.5 A/m2 and frequencies ranging from 200 Hz to 1000 Hz. Gradient re‐phased, spin echo, and echo‐planar sequences were tested to maximize the expected output signal. The images were subjected to statistical analysis to determine a set of parameters which produce detectable signal with minimal injected currents. Results: The expected signal was observed in agreement with the simulation. The agar phantom proved to be more stable and showed consistency in the imaging results. A large number of variables, including imaging sequence parameters, experimental setup parameters, and phantom quality, requires a more thorough analysis of the proposed technique. Conclusions: We have demonstrated the feasibility of simultaneous magnetic resonance and electrical impedance imaging that has the potential to revolutionize current Magnetic Resonance Mammography. A significant effort should be put into optimization of imaging parameters at minimum current without compromising patient safety or signal quality.
TU‐C‐330A‐08: X‐Ray Tube Induction Motor Performance in a 1.5 T MRI Fringe Field
Authors: Bracken J , Rowlands J
Published: July 2006

Purpose: To assess the performance of the induction motor of a rotating‐anode x‐ray tube in the magnetic fringe field of a clinical MRI scanner. The x‐ray tube must be placed in the fringe field near the entrance of an MRI scanner so that a hybrid x‐ray/MRI system for use in percutaneous aortic valve replacement in aortic stenosis patients can be constructed. Method and Materials: A standard rotating‐anode x‐ray tube insert was placed into the fringe field of a 1.5 T unshielded research MRI scanner. The induction motor in the x‐ray tube was aligned so that the magnetic field lines were in the plane of its stator core. The induction motor of the x‐ray tube was placed in magnetic fields ranging from 0 to 500 G. The magnetic fields were measured with a Model 4048 Gauss meter. The rotation speed of the anode was measured using a strobe light. The power consumed by the motor during operation in the fringe field was measured separately using a PLM‐1 power meter. The fringe fields of an actively shielded clinical 1.5 T scanner were measured with the Gauss meter and compared to the fields applied to the motor. Results: The anode rotation speed dropped from 3437 +/− 6.8 rpm to 2744 +/− 5.3 rpm when the magnetic fringe field was increased from 0 to 400 G. The average power consumed by the motor increased from 70.5 +/− 0.4 W to 78.2 +/− 0.1 W when the fringe field was increased from 0 to 500 G. Conclusion: This work indicates the feasibility of safely operating an x‐ray tube induction motor in the fringe field of an MRI scanner. Power consumption did not significantly increase and anode rotation speed did not fall below 3000 rpm until a fringe field exceeding 300 G was applied.
TU‐C‐330A‐09: Performance of CT and MR‐Based Assays for In Vivo Agent Concentration Quantitation
Authors: Zheng J , Dunne M , Allen C , Jaffray D
Published: July 2006

Purpose: To investigate the feasibility of performing longitudinal image‐based measurements using CT and MR to estimate contrast agent concentrations in organs and tissues in vivo. Method and Materials: A CT and MR contrast agent (200 mg/kg of iodine and 16 mg/kg of gadolinium encapsulated in liposomes) was administered intravenously to a 2 kg New Zealand White rabbit. At 5 minutes, 24, 48, 72, 96, 120 and 168 hours following contrast injection, the rabbit was imaged in CT (120kV, 200mA) and in MR (3D FSPGR, TR/TE= 9.8/4.3). 1mL of blood was collected from the same rabbit at each of the above times. The rabbit liver and spleen were harvested at the study end point (168 hours). The blood and tissues samples were then analyzed using high performance liquid chromatography (HPLC) to measure iodine content and inductively coupled plasma atomic emission spectrometry (ICP‐AES) to measure gadolinium content. Results: The differential blood CT attenuation vs. plasma iodine concentration correlation was well approximated with a linear fit (R2=0.9), while the differential blood MR signal intensity vs. plasma gadolinium concentration correlation was found to be nonlinear. These correlations were used to estimate the iodine and gadolinium content in the liver and the spleen. Using the CT correlation, the liver and the spleen iodine content were estimated to be 70% and 60% of the extracted amounts, respectively. The MR‐based method did not yield satisfactory gadolinium content estimates. Conclusion: This study attempted to correlate CT attenuation and MR signal increases to local iodine and gadolinium concentrations, respectively. In CT, the linear correlation obtained with blood data allowed for estimation of iodine content in the liver and spleen to 60–70% accuracy. In MR, although the presence of the contrast agent could be detected visually over a 7‐day period, additional effort is required to achieve reliable agent concentration estimations.
TU‐C‐330D‐01: Advances in Breast Imaging
Authors: Shaw C
Published: July 2006

Despite development and advances of new modalities, x‐ray mammography remains the main screening tool for early detection of breast cancers. It also continues to play an important role in the diagnosis and management of breast cancers. X‐ray mammography has relied on the use of high resolution screen/film combinations. Such techniques, although improved over the years, have the drawbacks of all the inconveniences and inflexibility associated with the use of film for image acquisition, storage and display. Motivated by search for better image quality and a general move towards filmless radiology, various digital mammography techniques have been developed, investigated and commercialized. These techniques can be largely divided into four types: amorphous silicon and selenium flat panel detector, amorphous silicon and cesium iodide flat panel detector, CCD and cesium iodide based slot scanning system, and storage phosphor imaging technique with dual‐side image read out. Each of these systems has its unique advantages and disadvantages and achieves various degrees of clinical implementation. Typical of all digital mammography techniques is the potential compatibility with digital image archival, retrieval and distribution systems. Furthermore, the acquisition of breast images in digital format has begun to facilitate the development and investigation of many advanced imaging techniques. Among them, dual‐energy mammography techniques have been developed to quantify breast tissue composition or to separate calcifications from the overlying tissue structures. Stereo‐mammography has been developed to use two projection views to provide a 3‐D perspective of the breast tissue structures, thus reducing the problem of overlapping structures. Tomosynthesis imaging pushes the idea of 3‐D imaging further by acquiring 10–25 projection views and use them to synthesize images to depict the breast structures as a number of thick layers. More recently, cone beam breast CT has been developed and investigated to scan the breast in a dedicated manner and provide true 3‐D images of the breast. Along a different direction, the development and investigation of various contrast mammography techniques have allowed x‐ray imaging to be used to image and study breast vasculatures as possible indication of breast cancer.

In this presentation, we will try to achieve the following educational objectives:

1. Review the development and investigation of major digital mammography techniques.

2. Review the development and investigation of various advanced breast x‐ray imaging techniques.

Research sponsored by the National Cancer Institute and the National Institute of Biomedical Imaging and Bioengineering.
TU‐C‐ValA‐03: Concurrent Multimodality Image Segmentation
Authors: El Naqa I , Bae K , Zheng J , Khullar D , Bradley J , Grigsby P , Low D , Deasy J
Published: July 2006

Purpose: Generally, in MRI, PET, and CT image datasets, more information is available for defining the target volume (or normal structures) than is used during the target segmentation. We introduce a method to take advantage of all the imaging information available for target segmentation, including multi‐modality images or multiple image sets from the same modality. Method and Materials: We generalized the multi‐valued level set deformable model (Chan et al., JVCI (2000) 11:130–141) for simultaneous 2D/3D segmentation/registration of multi‐modality images consisting of a combination of PET, CT, or MR datasets. Information from multi modality image sets is combined to define the final target volume. The method was evaluated on three patient cases, including: a non‐small cell lung cancer case with PET/CT, a cervix cancer case with PET/CT, and a prostate patient case with CT and MR. Results: In the case of the lung tumor the level set algorithm took 120 iterations for convergence, while in the case cervix tumor it converged after 30 iterations because the tumor has a deformed circular shape. In the prostate case, it took 50 iterations to converge and the results were made more sensitive to the shape prior information, because MR provides less gradient strength than PET. The computational time was on the order of few seconds in all cases. Conclusion: We a developed a new target segmentation algorithm which uses information simultaneously from multiple modalities. Our initial results indicate that the algorithm is promising and could provide physicians with a reliable contouring tool for lung, cervical, and prostate cancer.

This research was partially supported by NIH grant R01 CA85181 and a grant from TomoTherapy, Inc.
TU‐C‐ValA‐06: Quantifying the Properties and Accuracy of a Deformable Image Registration Algorithm for 4D Treatment Planning
Authors: Wijesooriya K , Weiss E , Dill V , Dong L , Mohan R , Joshi S , Keall P
Published: July 2006

Purpose: A necessary tool to facilitate automated four‐dimensional and adaptive radiotherapy planning is deformable image registration (DIR). The purpose of the current study was to quantify the accuracy of a DIR algorithm by comparing automatically transferred and manually segmented structures on 4DCT images. Method and Materials: 780 structures were manually segmented on thirteen patient 4DCT image sets each consisting of 10 respiratory phases. A large deformable diffeomorphic DIR algorithm, integrated with a commercial treatment planning system, was used to map each CT set from the inspiration respiratory phase CT image set respiratory phase images. The calculated displacement vector fields were used to deform and transfer structures defined on the inspiration CT to the other respiratory phase CT image sets. The manually and automatically segmented structures were compared using volumetric, displacement, and surface congruence metrics. Results: Deformation with respiration was observed for the lung tumor and normal tissues. This deformation was verified by examining the mapping of high contrast objects, such as the lungs and cord, between image sets. The auto‐ and manual methods showed similar trends, with a smaller difference observed between the GTVs than other structures. The auto‐contoured structures were more consistent both in terms of centroid displacement and volume as a function of respiratory phase than manual contours. 1.6% of the time, deficiencies of manual contouring has been detected using auto contouring. Image artifacts play a crucial role in auto contouring. Conclusion: An automated system is established to auto‐contour structures starting from one 4DCT image phase to other 4DCT image phases. The auto‐contoured structures generally agree with the manually drawn structures. However the auto‐contoured structures are more consistent in trajectory and volume, and also highlighted some large errors in the manually drawn contours. Careful assessment is needed in the presence of 4DCT artifacts.
TU‐C‐ValB‐03: The Dosimetric Impact of Intrafractional Motion On IMRT Treatment of Prostate Cancer
Authors: Melancon A , Dong L , de Crevoisier R , O'Daniel J , Kudchadker R , Newhauser W , Tucker S , Lee A , Cheung R , Mohan R , Kuban D
Published: July 2006

Purpose: To quantify the dosimetric impact of intrafractional motion on reduced‐margin IMRT treatments of prostate cancer. Methods and Materials: CT images were acquired immediately before and after a daily treatment for 46 prostate cancer patients. These CT sets were registered to the bony anatomy of the patient using an in‐house 3D image registration software. To test the hypothesis that a 3‐mm isotropic target margin would adequately cover the target over the duration of the treatment, an 8‐field IMRT plan was designed on the pre‐treatment CT and subsequently copied and re‐calculated on the post‐treatment CT. For convenience of comparison, dose plans were designed to receive a full course of treatment (75.6Gy). Dosimetric impact was assessed with comparisons of prostate, seminal vesicle (SV), rectum, and bladder volumes receiving several dose levels as well as the minimum and maximum doses to 0.1cc of the prostate and SV. Anatomic variations were also quantified. Results: Over the duration of one treatment fraction (21.4+/−5.5 minutes), there were systematic reductions in the volumes of the prostate and SV receiving the prescription dose (1.8 and 7.2 % respectively, P<0.001) as well as the minimum dose to 0.1cc of their volumes (2.1 and 6.4Gy, P<0.001). Of the 46 patients, 4 patients' prostates (91%) and 8 patients' SVs (83%) did not maintain dose coverage above 70Gy. Rectal dose increased and dose to the percentage‐volume of the bladder decreased at all dose levels. Rectal volume filling was correlated with a decrease in percentage‐volume of the SV receiving 75.6, 70, and 60Gy (P<0.001, P<0.001, P=0.02). Conclusion: With a 3‐mm intrafractional margin, a considerable percent of patients will not receive full dose coverage. The rectal volume increase during a treatment fraction has significant dosimetric impact on SV dose coverage and rectal sparing. Proactive immobilization of the rectum during treatment may be warranted.
TU‐C‐ValB‐04: Margin‐Less Prostate IMRT Plans, Directly Optimized for TCP and NTCP Including Geometric Uncertainties
Authors: Witte M , van der Geer J , Schneider C , Lebesque J , Alber M , van Herk M
Published: July 2006

Purpose: To account for geometric uncertainties without the use of margins during IMRT planning such that optimal values are obtained for the population averaged TCP and NTCP functions. Methods and materials: A new method of computing cost functions was implemented within the IMRT planning tool Hyperion. Population‐averaged values of biologic score functions (TCPpop and NTCPpop) are optimized, simulating random errors by blurring the dose, and systematic errors by displacing target and OARs relative to the dose distribution.

For 19 prostate (and seminal vesicle) patients, treatment plans for a five beam setup were created, optimising TCPpop while constraining rectum NTCPpop and the maximum dose to the target. Gaussian distributions were used for the systematic and random errors (translations only, no attempt was made to model rotations or deformations). Since geometric uncertainties were accounted for within the cost functions, no CTV to PTV margin was used. For comparison, conventional plans were created using a CTV‐to‐PTV margin (M=2.5Σ+0.7σ) and a Simultaneous Integrated Boost (SIB) technique (68Gy to the above PTV, 78Gy to PTVboost with 5mm margin, 0mm towards rectum). The resulting plans were evaluated using an independent tool that simulates the effects of geometric uncertainties. Results: Compared to conventional plans, our new technique reduced the planned dose to the rectum, while increasing the volume receiving 78Gy. We ensured that TCPpop of the new technique was not smaller than for conventional techniques. The average rectum NTCPpop values were 14% (margin recipe), 8% (SIB), and 4% (new technique), for average TCPpop values of 69%, 70%, and 71%. Conclusions: The computation of TCP and NTCP including knowledge of geometric uncertainties within the inverse IMRT optimization loop is feasible (less than 1 hour optimization time), and results in robust prostate treatment plans with an improved balance between local control and rectum toxicity.
TU‐C‐ValB‐07: Evaluation of 4DRT: CT Acquisition and Gated Delivery System
Authors: Bayouth J , Sample J , Waldron T , Siochi R
Published: July 2006

Introduction: Our objective was to characterize retrospectively acquired 4DCT data for prospective gated delivery, and the effects of gate length on beam energy stability, output constancy, and positional accuracy / inter‐device constancy. Materials and Methods: A barometric sensor gated the Siemens Oncor linac and Siemens Sensation CT scanner. Respiratory motion of 20 mm at 15 bpm over a stationary jig was used to assess radio‐opaque marker positions. Retrospective 4DCT reconstructions were obtained at 6 phases of inspiration and expiration, ranging from 0% to 100% by 20% intervals. The center of the pin was identified using 50% threshold values on the CT dataset. On the linac, gate windows of 1500, 850, 500, 350, 300, and 250 ms for the 12 phases were studied. Ion chambers were used to measure the beam energy and output stability at 10 cm and 20 cm in solid water simultaneously. Marker position during gated delivery was determined via film. Nine profiles, centered around the marker, were extracted for both the static and moving axes. The averages were smoothed, and the peak position and full‐width‐at‐half‐maximum (FWHM) were determined. The difference in FWHM along the static and moving axis is the intra‐gate motion. Results: Dosimetry for gates >= 500 ms was excellent. Although the average energy was constant, gate length reduction from 500ms to 250 ms resulted in an energy standard deviation increase of 1–14%, an output constancy increase from 1.6% to 4.6%, and a 50% dose rate decrease. Mean discrepancies between marker position measured on CT and linac were 3 mm, with 8 mm maximum. Conclusions: Dosimetric characteristics of the linac are reasonable for gating windows ⩾ 500 ms. Target position measured on retrospective 4DCT can introduce significant uncertainty for several phases of the respiratory cycle.
TU‐C‐230A‐01: Introduction to Medical Errors and Implications
Authors: Dunscombe P
Published: July 2006

There has developed, over the last few years, an increased awareness of the risks patient take when submitting themselves to medical procedures all of which are prone to errors. As a medical intervention, radiation therapy is no less susceptible to errors than any other branch of health care. Indeed in the case of radiation therapy both the consequences of errors and the number of patients affected can easily exceed those experienced elsewhere. A relatively small deviation from the prescription in either dose or volume irradiated can result in severe side effects or a failure to achieve the desired therapeutic outcome. Many patients are planned and/or treated on the same equipment facilitating the possible exposure to systematic effects.

In this presentation the current status of error prevention activities in radiation therapy will be reviewed. This will include initiatives in both North America and Europe. The AAPM has recently formed a working group to focus on this issue. In Europe, ESTRO is particularly active in this area through workshops, teaching courses and the ROSIS database. In addition there are less formal groups who are dealing with particular components of safety in radiation therapy.

If we are to live by the maxim “First, do no harm” then we need to do better than we are doing now. The degree of ambiguity in the available literature confounds interpretation in many cases. In particular we need to speak the same language when describing safety/quality issues. We need to have a metric for describing the severity of incidents in radiation therapy. One will be suggested for discussion. Ideally we should have a causal structure, which could be linked to a high level process map, for investigating incidents. With a causal structure we have a much better chance of learning from the actual and potential incidents which do occur. The learning component is one that we are particularly weak at. With a better understanding of the probability and severity of incidents we will make more informed decisions on the allocation of safety/quality resources. Finally, patient safety in radiation therapy is too big to deal with effectively on an individual clinic basis. While local issues undoubtedly influence the local risk of incidents, we will be able to give our patients a far better guarantee of both a safe and effective treatment if we work together across professional and geographic boundaries. To do this we need a common taxonomy, a degree of commonality in causal analysis and a common commitment to effective learning strategies.

Learning Objectives:

1. To appreciate the current status of error reduction activities in radiation therapy.

2. To identify some of the limitations of current activities.

3. To consider approaches to improving error reduction strategies.
TU‐C‐224A‐02: Aperture‐Based Beam Delivery for Intensity Modulated Proton Therapy
Authors: Fan J , Li J , Luo W , Fourkal E , Stathakis S , Lin T , Ma C
Published: July 2006

Purpose: Treatment planning for intensity modulated proton therapy (IMPT) has traditionally used an approach in which the intensity and energy for each beamlet are modulated, which requires high dose‐rate beam scanning capabilities. The purpose of this work is to develop a new proton beam delivery method for IMPT without the need for high dose rate beam scanning. Method and Materials: In this study, an aperture‐based method to deliver a uniform dose to a target volume has been investigated. For a target with a flat back surface, a broad proton beam is collimated with an aperture conformed to the cross‐section of the target at a specific depth. The proton beam has a small energy spread to cover a 0.5–1.0 cm depth range. The mean energy and the weight of each proton beam are varied to produce a uniform dose distribution in the whole target volume. For an irregularly shaped target located in patient body, a compensator is used to provide equal beam path lengths to the back surface of the target. This will create an equivalent back surface for the target and then it can be treated in the same way as for the target with a flat back surface. A Fluka based Monte Carlo package has been used for dose calculation in aperture‐based IMPT treatment planning. Results: We have tested aperture‐based IMPT planning on a variety of patient cases. The results demonstrate that it can produce highly conformal dose distributions using only five to six apertures per beam direction. As compared with scanning beam delivery, our studies demonstrate that aperture‐based beam delivery can result in a significant reduction in both the number of beam segments and the number of monitor units. Conclusions: Aperture‐based IMPT optimization results in highly efficient treatment delivery while maintaining the dosimetric benefits of IMPT.
TU‐C‐224A‐05: Dosimetry Comparison of the Newly Implemented Multi‐Criteria Optimization Tool for IMRT Planning
Authors: Yang C , Peng L , Lauterbach M
Published: July 2006

Purpose: To apply a biological model based algorithm for acquiring optimized IMRT planning solutions. This interactive planning tool will help users to select the best available plans in the IMRT solution space.

Method and Materials: IMRT often is a time consuming iterative optimization process between evaluation of the dose distribution and redefinition of the object function. An IMRT planning optimization tool (Multi‐Criteria Optimization, MCO™) has been introduced for non‐clinical evaluation to acquire the best available solutions. Based on a Pareto's solution concept, this tool could search the solution space and offer users a limited set of deliverable IMRT plans. With this interactive process, users can set the target and critical structures dose constraints with the biological model (EUD) to obtain the best solution. We used Pinnacle system as the benchmark to compare the dosimetric gain from the MCO algorithm, DVH indicated excellent sparing with better PTV coverage is achievable from the MCO process in KonRad system.

Results: Dosimetric findings are summarized as 1) MCO optimization testing shows that much better dose distribution can be achieved compared to the current planning results (Fig. 1 and Fig. 2). Due to the confined solution space, the optimal results are easily achievable. 2) MCO with Pareto's approach is durable in the solution searching process. It is interactive with the graphical interface which the dose distribution along with the DVH can be compared simultaneously (Fig. 3). 3) IMRT dose optimization and summary based on the MCO methodology are very conceivable. With pre‐calculated IMRT solutions, final results help users to select the best available plan from the solution domain in real time (Fig. 4). Conclusion: From this interactive MCO planning tool, we can calculate the best IMRT results in a very reasonable time frame. Human factors for determining an acceptable plan can be dramatically reduced.
TU‐C‐224C‐02: A Practical and Accurate 3D Dosimetry System for Radiation Therapy
Authors: Guo P , Adamovics J , Oldham M
Published: July 2006

Purpose: At present, clinical dosimeters are limited to point or planar measurement, and hence do not provide the comprehensive 3D information ideal for verification of advanced delivery techniques. In this work we present a clinically viable 3D dosimetry system comprising a PRESAGE™ dosimeter with read out by an optical‐CT scanner. Method and Materials: A novel solid dosimeter called PRESAGE™ has been developed which is composed of polyurethane polymer and radiochromic leuco dyes. PRESAGE™ exhibits a stable color change and hence optical density (OD) change when exposed to ionizing radiation. A PRESAGE™ cylinder of 16cm diameter × 11cm height was taken through the treatment planning process and a 5‐field 6MV conformal radiation treatment was delivered by a Varian® linear accelerator. The radiation induced OD change was imaged in 3D by an optical‐CT scanner and this measured distribution was then compared with the corresponding dose distribution calculated by the treatment planning system, as well as to independent measurement by GAFCHROMIC® film. Intercomparisons between the three dose distributions were made by superimposing isodose lines and calculating gamma maps (with criteria 4% dose difference and 4mm distance to agreement). Results: Given stable temperature and protection from exposure to incandescent light, the dose response of PRESAGE™ was observed to be robust to all aspects of the lab. The 3D dose distribution measured in PRESAGE™ showed good agreement with the calculated treatment plan (Eclipse) as well as the independent film measurement at all percent doses >30% (i.e. in regions further than 1cm from the wall). Gamma comparison shows that the PRESAGE™ measurement agrees with both the calculation in treatment plan and the film measurement within 4% dose difference and 4mm distance to agreement. Conclusion: This work presents the PRESAGE™/optical‐CT combination as a practical 3D dosimetry system which can provide comprehensive quality assurance of advanced treatment techniques.
TU‐C‐224C‐03: Dose Dependence of MOSFET Calibration Factor Between 30kV and Cobalt‐60 Irradiation
Authors: Lavallee M , Gingras L , Beaulieu L
Published: July 2006

Purpose: To characterize the behavior of MOSFETs under radiation of various clinically relevant energies used in radiotherapy and radiology by evaluating its sensitivity or threshold voltage shift (CF) with regard to total integrated dose. Method and Materials: Seven p‐type, duals bias MOSFETs from Thomson & Nielsen were investigated. They were exposed to four radiations sources: (1) 60Co unit (〈E〉γ: 1.25 MeV), (2) 192Ir HDR unit (〈E〉γ;: 0.38 MeV), 30 kV beam (〈E〉γ: 14.8 keV) and (4) 150 kV beam (〈E〉γ: 70.1 keV). The MOSFET's sensitivity (CFw) was evaluated at various moments in time and was calculated as the ratio of the measurement Mw (mV) over the estimated dose value Dw (cGy) both in water. Results: The sensitivity of MOSFET is express by their calibration factor (CFw), and allows the user to associate the reading displayed by the device (mV) to a dose value (cGy). The CFw value diminishes with increasing threshold voltage, especially for low energy radiation. It is stable for 60Co irradiations, while it decreases of 6%, 5% and 15% for beam energies of 192Ir, 150 kV and 30 kV respectively. This behavior is explained by an alteration of the effective field applied on the MOSFET (bias), caused by the accumulation of holes at the SiO2 interface. It is strongly dependent on the radiation nature (LET) and particularly affects low x‐ray energies. Conclusions: Those results are of major interest since, following the company recommendations to calibrate the device every 7 000 mV, it could lead to a significantly underestimated dose. A calibration of the device before every use and performing more than one measurement (thus using a mean dose value) should compensate the observed behavior.
TU‐EE‐A4‐03: Quality Control Testing of Diagnostic Ultrasound Systems: Experience in Testing 72 Systems in 11 Years
Authors: Lu Z , Nickoloff E , Dutta A , So J
Published: July 2006

Purpose: The goal is to assess the necessity and relevance of QA/QC testing procedures for diagnostic ultrasound systems. Methods and Materials: The ultrasound QA/QC program at our institute was reviewed in this paper. Over the past 11 years, 72 diagnostic ultrasound systems have been included in the QA/QC program. Acceptance tests were conducted in newly installed systems. In some situations, final payment was withheld to ensure the correction of the deficiencies revealed during the acceptance testing. Periodic QC reports were sent to the in‐house engineer group and corrective actions were taken and documented. Our testing procedures included B‐mode tests on distance accuracy, maximum depth of penetration, spatial resolution, contrast lesion detectability, image uniformity, dead zone, image display/soft copy fidelity and other physical and mechanical inspections. In addition, Doppler mode tests were performed on some units to measure the Doppler signal sensitivity, angle accuracy, gray‐scale image congruency, range‐gate accuracy and flow readout accuracy. Results: A total of 84 deficiencies were documented on those units older than 5 years (1.8 deficiencies/unit‐year) and 183 deficiencies on the units with ages of 5 years or less (1.0 deficiencies/unit‐year). These problems were classified in categories according to the QC tests and the percentage distribution of each category was calculated. While the overall image quality deterioration revealed through spatial resolution and contrast lesion detectability testing topped the deficiency category list for older units, a significant increase in transducer deficiencies was observed on newer modern state‐of‐art units. This observation was consistent with the increasing complexity in rapidly advancing transducer technology in recent years. QA/QC procedures appeared able to reveal problems at their early stage before these problems would severely interfere with clinical practices. Conclusion: This experience of ultrasound QA/QC program at our institute confirms the necessity to have a comprehensive QA/QC program for diagnostic ultrasound systems.
TU‐EE‐A4‐04: Comparison of the CT Scatter Fractions Provided in NCRP Report No. 147 to Scanner‐Specific Scatter Fractions and the Consequences for Calculated Barrier Thickness
Authors: Larson S , Goodsitt M , Christodoulou E , Kim J , Larson L
Published: July 2006

Purpose: NCRP Report No. 147 provides fixed values of the scatter fraction per centimeter (κ) for the peripheral axis of the head and body CT phantoms. This study was performed to determine scatter fractions for different makes and models of CT scanner and to examine the consequence of any differences in κ on a typical shielding calculation. Method and Materials: κ values for five GE CT models, four Siemens CT models and one Toshiba CT model were determined. They were calculated using an equation for the scattered air kerma at 1 m from NCRP 147 (Kermascatter=κ*ScanLength*CTDI100/pitch) and using scattered air kerma data provided by the manufacturers and measured CTDI100 (periphery) values. Typical barrier calculations, following NCRP 147 methodology, were performed for each CT scanner using the fixed κ values and, separately, using the calculated scanner‐specific values. Results: The κ values from NCRP 147 are 3×10−4/cm and 9×10−5/cm for the periphery of the body and head phantoms, respectively. Calculated κ values varied from 3.2×10−4 to 5.2×10−4/cm for the body and 5.6×10−5 to 1.1×10−4/cm for the head. The results of a typical barrier calculation indicate that for the scanners studied, the fixed κ values produced lead barrier thicknesses that ranged from 0 to 0.2 mm less than those determined from scanner‐specific κ values. Similar calculations for the floor gave a maximum underestimate of 1.2 cm. Conclusion: The actual κ values of a specific CT scanner can vary significantly from the fixed values provided in NCRP 147. Using the fixed values for some scanners may slightly underestimate the required barrier thickness. Any small underestimate in barrier thickness would likely be more than compensated by a conservative estimate of the scanner's workload.
TU‐EE‐A4‐05: Monte Carlo Calculation of the Organ and Effective Doses for Pediatric Patients Under Helical CT Exams
Authors: Lee C , Lee C , Bolch W
Published: July 2006

Purpose: As it gains more popularity as a diagnostic modality, helical multi‐slice CT can potentially impose a significant patient dose especially to pediatric populations. Even though simple acryl phantoms have been used to estimate relative radiation risks to the patient, very few studies have investigated accurate age‐dependent organ absorbed doses. This study was intended to assess individual organ dose as well as the effective dose under typical CT exams using realistic tomographic phantoms of pediatric patients. Method and Materials: Five ORNL stylized phantoms and five realistic UF tomographic phantoms of pediatric patients were prepared for the use with MCNPX general Monte Carlo code. A FORTRAN subroutine was written to explicitly simulate the helical motion of the multi‐slice CT x‐ray source. Ion chamber measurements provided the normalization factors for the Monte Carlo simulation results. Three tube voltages (80 kVp, 100 kVp, and 120 kVp), two collimated beam thicknesses (12 mm and 24 mm), and two filter (head filter and body filter) combinations were simulated for each of the ten phantoms. Results: The study data showed that the effective dose increased on average 110% when the tube voltage changed from 80 kVp to 100 kVp at the same tube current setting, while the 120 kVp imposed on average 53.8% higher dose than the 100 kVp tube settings in the CAP CT exams. The ORNL phantoms and the UF phantoms showed distinctive dosimetric characteristics under chest and abdomen CT exams. The cause of these differences is explained by the unrealistic torso thicknesses of the ORNL stylized phantoms. Individual organ equivalent doses are also calculated and compared between the two types of phantoms. Conclusion: Detailed organ doses and effective doses were calculated for pediatric patients under helical CT using various anthropomorphic computational phantoms and Monte Carlo code.
TU‐EE‐A4‐06: Analysis of Dose‐Related Data Logged for Fluoroscopic Cardiac Interventional Procedures
Authors: Dohatcu A , Bednarek D , Rudin S
Published: July 2006

Purpose: In response to FDA advisories of the potential for skin injuries from fluoroscopically‐guided interventions, logs have been recorded of procedure‐related information for all fluoroscopic cardiac studies performed at our hospital. The data includes dose‐area product (DAP), estimated entrance‐skin dose (ESD), fluoroscopy time, number of digital runs, image‐intensifier magnification mode, and patient weight and height as well as procedure type and physician. Method and Materials: Dose‐related data was recorded for over 2000 cardiac catheterization and over 800 electrophysiology procedures. This information was transferred to a database spreadsheet and analyzed to determine distribution shape, range and median values and correlations between factors. ESD values were calculated from DAP readings using the estimated field size at the patient entrance and included backscatter. Fluoroscopy times and dose values are compared by procedure and physician. Those procedures evaluated included percutaneous‐coronary interventions (PCI) performed in the catheterization laboratory and radiofrequency ablation (RFA) and biventricular‐implantable‐cardioverter defibrillator (BIV ICD) placement performed in the electrophysiology lab. Results: All procedures had a wide range of DAP values, ESD values and fluoroscopy times with distributions skewed toward the lower end. PCI procedures generally had the greatest ranges (216 to 88,971 cGy‐cm2 DAP, 2 to 726 cGy ESD, 1 to 96 minutes fluoroscopy) and the highest median values (16,000 cGy‐cm2, 130 cGy, 20 minutes). There was some correlation demonstrated between DAP values and fluoroscopy time and patient body mass index. ESD values calculated from DAP values had a large uncertainty primarily due to uncertainty in the exposure geometry. Conclusion: Although an inexact measure of skin exposure during interventional procedures, DAP values provide some guidance in identifying those patients with ESD values potentially above thresholds for deterministic effects. Tracking of this parameter can provide an indicator of when cautionary notes should be placed in the patient's chart for medical observation and followup.
TU‐E‐330D‐01: TLD‐100 Measurement and Assessment of Internal Mouse Dosimetry During Micro‐CT Analysis
Authors: Daibes Figueroa S , Winkelmann C , Miller W , Rold T , Sieckman G , Smith C , Ma L , Garrison J , Volkert W , Hoffman T
Published: July 2006

Purpose: Because Micro‐CT utilizes ionizing radiation for image formation, radiation exposure during imaging is a concern. The objective of this study is to quantify the radiation exposure delivered during a Micro‐CT scan and to assess potential therapeutic effects associated with this radiation dose in a murine cancer model. Materials and Methods: Radiation exposure was measured using calibrated thermoluminescent dosimeters (TLD‐100) irradiated during a typical Micro‐CT scan protocol. TLD calibration curves were generated with a Cs‐137 irradiator. TLD's were implanted into a euthanized mouse and was imaged with Micro‐CT. TLD's were removed post‐scan and analyzed. Internal exposures were converted to dose in water. A C57BL/6 mouse lung tumor model derived by IV injection of 400,000 B16F10 murine melanoma cells was assessed for survivability and potential therapeutic effects due to absorbed radiation doses during Micro‐CT imaging. Results: A single Micro‐CT scan dose of 7.8±0.5 cGy was achieved when using a lucite anesthesia support module and a dose of 9.2±0.6 cGy with out the use of the anesthesia module. TLD data was validated using an ion chamber, providing measured radiation exposures of 8.1±0.4 cGy and 9.7±0.5 cGy with and with out the anesthesia module, respectively. Internal TLD analysis demonstrated an average mouse organ absorbed dose of 7.3±0.6 cGy. Conclusions: Survival analysis demonstrated a mean survival of nontreated control animals of 29±2 days, with animals receiving up to five sequential Micro‐CT studies surviving a mean of 30.5±1.5 days (total estimated dose of 39±2.5 cGy). The calculated cell survival fraction for a 9.2 cGy Micro‐CT scan was 99.25%. Therefore, negligible therapeutic effect from the radiation exposure delivered during Micro‐CT analysis was observed in the animal model investigated.
TU‐E‐330D‐03: Evaluation of An OSL Dosimetry System for CT Quality Assurance and Dose Optimization
Authors: Peakheart D , Rong X , Yukihara E , Klein D , McKeever S , Ramji F
Published: July 2006

Purpose: Recent development of wide‐beam multidetector CT and conebeam CT demands alternative methodology to CTDI. In this study, the Optically Stimulated Luminescence (OSL) technique was evaluated for CT quality assurance and dose optimization. Method and Materials: CT scans were performed on 38‐mm2 thin Luxel™ dosimeters oriented in axial plane of a GE LightSpeed Ultra and at the center of a CT body dosimetry phantom. A 5‐mm beam collimation was selected to determine the energy response of the OSL detector at 80, 120, and 140 kVp stations. mA response of the OSL detector was evaluated from 60 to 350 mA. Helical scans of varying length coverage were also performed with the detector placed at the isocenter. The exposed OSL discs were measured using a Riso TL/OSL‐DA‐15 reader. Each OSL measurement was followed by a standard beta source irradiation and subsequent OSL measurement to normalize for the differing mass of the disks. The normalized OSL signal reading was used in the data analysis. Results: Good mA linearity was observed at all 3 kVp stations. There are discontinuities seen at ∼ 250 mA and it is known to be caused by tube focal spot change. The 120 and 140 kVp data show good correlation with ionization chamber reading. For 80 kVp, OSL signals to ion chamber readings are all higher, particularly at low mA range, indicating higher sensitivity of the OSL detector over the ion chamber. The helical scans show an increased OSL signal with scan length and a leveling of the signal at large scan coverage. Conclusion: The OSL detectors are of small size and responded well to CT exposure. It provides a practical technique for quantifying the dose at any location of a phantom for quality assurance and hence exhibits a potential for estimating patient organ dose.