bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐A‐210A‐01: Management of Interventional Equipment and Suite: Cradle to Grave
Authors: Strauss K
Published: April 2010

The life of any fluoroscopic imaging device begins with someone's perceived need for it and ends when it is removed from the clinical environment. In between these “cradle and grave” milestones, the machine must meet clinical objectives, provide good image quality, and reduce radiation dose to both patients and personnel. An organized program that achieves cost effective quality improvement is required to achieve these objectives. The first step identifies the clinical requirements of the imager. This identification assists obtaining adequate project funding. One acquires the imager by identifying the vendor of choice, negotiating the purchase, and issuing a purchase contract. One concurrently must plan an effective and efficient supporting facility followed by monitoring of the progress of renovation/construction. After the unit is installed, the owner acceptance tests the imager followed by staff training. A comprehensive program of routine testing, maintenance, repair, and record keeping to assure equipment performance begins after commissioning of the unit and continues throughout its life.

Learning Objectives

1. Understand how to help physicians identify equipment attributes that address clinical needs.

2. Understand important steps in selecting, negotiating, and contracting the purchase of imaging equipment.

3. Understand basic elements of facility design necessary to support selected imaging equipment.

4. Understand the objectives of acceptance testing of state‐of‐the‐art imaging equipment.

5. Understand the basic elements of a program to assure equipment performance after its commissioning.
TH‐A‐213A‐01: Multi‐Modality Image‐Guided Near Infrared Spectroscopy: Optimization and Clinical Applications
Authors: Srinivasan S , Pogue BW , Carpenter C , Davis SC , Paulsen KD
Published: April 2010

Image‐guided near infrared spectroscopy (IG‐NIRS) provides deep tissue functional characterization at high resolution. This approach combines conventional imaging techniques such as MRI and CT with optical near infrared technologies, giving information directly relating to the vascular and metabolic status of tissue in‐vivo. The resultant estimates of total hemoglobin, oxygen saturation, water, lipids and scatter provide a window towards understanding the mechanisms of cancer in terms of angiogenesis, hypoxia, changes in the interstitium and cell organelle structural changes. This type of spectroscopy has been applied for breast cancer diagnosis and treatment monitoring, as well as image‐guided fluorescence in small‐animals.

Optimization of these systems is essential to provide quantitative and accurate spectroscopy. This optimization encompasses system design for simultaneous multi‐modality image acquisition, methods for intelligently combining spatial anatomical structure from MRI/CT into optical recovery, image segmentation, visualization and interpretation of novel combined optical and MRI/CT parameters.

This talk will provide an over‐view of these aspects of multi‐modality imaging as well as results from in‐vivo clinical applications.

Learning Objectives:

1. Understanding the rationale for multi‐modality IG‐NIRS systems

2. Understanding the type of information and contrast available through these systems

3. Understanding the challenges towards clinical use of these systems.
TH‐A‐213A‐02: Noninvasive Monitoring of Brain Tumor Therapy
Authors: Bullitt E
Published: April 2010

Monitoring the efficacy of brain tumor therapy is a clinical dilemma. Results of biopsy provide the most reliable indicator but biopsy is too invasive for frequent use. The clinical standard of practice is to perform serial magnetic resonance scans and to assess changes to tumor “size” as seen on gadolinium enhanced images, with “size” measured in one, two, or three dimensions. This review discusses the advantages and disadvantages of the three measurement methods as well as some of the effects of voxel size on the calculation. Problems inherent to the use of gadolinium enhanced images include the effect of steroids and the confounding appearance of radiation necrosis. The limitations of the approach have led multiple groups to explore alternative methods of assessing tumor activity.

Learning Objectives:

1. Understand the clinical standard of practice of monitoring brain tumor therapy from T1 gadolinium enhanced images and its strengths/weaknesses.

2. Understand some of the different experimental approaches, often involving different image types, to assessing tumor activity.
TH‐B‐211A‐01: Practical Considerations for Respiratory Colarated CT Imaging and Target Volume Delineation
Authors: Mutic S
Published: April 2010

Accurate and conformal treatment of tumors in abdomen and thorax is challenging due to respiratory related motion. Respiratory corralled CT imaging combined with gated treatment delivery can improve both accuracy and conformality of delivered dose distributions. Implementation of respiratory correlated imaging and treatment delivery can be performed in multiple ways and understanding of different techniques and technical challenges is critical for efficient and safe clinical implementation. Formal recommendations for commissioning and clinical use of this technology is scarce. Inadequate evaluation and understanding of these systems can lead to significant treatment errors. This presentation deals with practical issues of respiratory correlated CT imaging and commissioning. Examples of some commonly seen image artifacts are also discussed. Furthermore, contouring based on respiratory correlated images is discussed, again with examples of some of potential pitfalls and artifacts. Education Objectives:1. Commissioning process for respiratory correlated CT imaging and delivery techniques.2. Use of respiratory correlated images for target delineation.3. Common image artifacts and contouring errors seen with respiratory correlated imaging.
TH‐B‐BRC‐01: Tools for IMRT Commissioning: Static and Rotating Gantries
Authors: Ezzell G , Yin F , Xiao Y
Published: April 2010

Commissioning an IMRT system refers to the initial verification by phantom studies that treatments can be planned, prepared, and delivered with sufficient accuracy. Our profession has struggled since the inception of IMRT to define what measurements to make and what degree of accuracy is sufficient. Two AAPM task groups have been dealing with complementary issues. AAPM TG 120 is finalizing a report on dose measurement techniques for IMRT validation. AAPM TG 119 is finalizing a report that recommends a specific set of tests for IMRT commissioning and presents the results of those tests from several institutions in order to illustrate the accuracy that is achievable. The report presents a methodology for other facilities to perform the tests and determine if their achieved accuracy is comparable to this reference baseline.

The TG119 tests pose a range of optimization problems requiring simple to complex modulation patterns. The tests include mock prostate, head and neck, and para‐spinal geometries. Members of the group have planned and delivered the treatments using their local planning and delivery systems, and then assessed the resulting doses using broadly available dosimetry tools following a specified protocol. Measurements included ion chamber “point” doses and film dosimetry on selected planes for all fields irradiating the phantom. Institutions also evaluated dose distributions produced by individual fields using detector arrays, film, or EPID. Planar dosimetry results were analyzed with gamma criteria of 3% dose/ 3mm distance to agreement. The mean values and standard deviations of the results were used to develop confidence limits for the test results using the concept [Confidence Limit = |Mean| + 1.96 σ]. Other facilities can use the test protocol and results as a basis for comparison to this group.

Learning objectives for this presentation:

1. Describe the TG119 test suite, analysis protocol, and initial results.

2. Demonstrate how it can be applied by other facilities, including delivery with rotating gantries.

3. Provide examples of IMRT QA failures that can be identified and corrected using these processes.
TH‐C‐211A‐01: Designing Effective and Efficient Medical Imaging Physics Learning Activities
Authors: Sprawls P
Published: April 2010

The clinically effective and safe utilization of the medical imaging modalities requires a staff of radiologists, technologists, and medical physicists with the education and training to select appropriate technology, evaluate equipment performance, optimize procedures, and manage patient safety. Educational activities (classes, conferences, self‐study, interactive experiences, etc.) to develop these competences are characterized by their effectiveness and their efficiency.

The effectiveness of a learning activity determines outcome and the ability to perform functions as defined by the learning objectives. Effective learning is generally enhanced by providing an enriched learning environment that engages the learner with the imaging technology and the associated clinical activities. Elements that contribute to an enriched learning environment include clinical images, graphics for visualizing the invisible, interaction with feedback directly or through simulation, appropriate organization and structure of the engagement (concept development before quantization), and the guidance by a medical physicist as the learning facilitator. The elements and activities of the learning process should be organized to activate specific mental functions that collectively contribute to effective learning.

In most cases the development and conduction of a highly effective and enriched learning activity are compromised by issues of efficiency. These include availability of: qualified medical physics faculty at the place of need, limitations on time to develop educational materials, logistical constraints imposed by scheduling and conflicting clinical activities, and adequate access to the imaging technology for educational purposes.

In this symposium we will work through the general process of developing an educational activity to produce specific outcomes taking into account the issues of effectiveness and efficiency. A review of certain mental functions will provide the background for designing and organizing enriched learning environments. Applications of technology will be integrated into the design and demonstrated to enhance human performance of both the learners (students, residents) and the medical physics learning facilitators (teachers, mentors).

Learning Objectives:

1. Establish appropriate learning objectives based on the needs associated with the learning activity.

2. Understand the various functions of the human brain that need to be considered in the development of learning activities.

3. Describe the characteristics and give examples of an enriched learning environment.

4. Design a learning environment that maximizes the effectiveness of the planned learning activity.

5. Include in the design appropriate utilization of technology to increase the efficiency of learning activities.

6. Apply the design principles developed in this symposium to your specific educational programs.
TH‐C‐211A‐02: Writing and Reviewing Medical Physics Papers
Authors: Hendee W , Karellas A , Rogers D , Slattery P
Published: April 2010

There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation of a scientific manuscript will be dissected so participants can appreciate how each part is developed and then assembled into a complete paper. Then the review process for the paper will be discussed, including how to examine a paper and write an insightful and constructive review. Finally, we will consider the challenge of accommodating the concerns and recommendations of a reviewer in preparing a revision of the paper.

A second feature of the workshop will be a discussion of the process of electronic submission of a paper for consideration by Medical Physics. The web‐based PeerX‐Press engine for manuscript submission and management will be examined, with attention to special features such as EPAPS and line referencing. Finally, new features of Medical Physics will be explained, such as Vision 20/20 manuscripts, Physics Letters and the standardized formatting of book reviews.

Learning Objectives:

1. Improve the participants' abilities to write a scientific manuscript.

2. Understand the review process for Medical Physics manuscripts and how to participate in and benefit from it.

3. Appreciate the many features of the PeerX‐Press electronic management process for Medical Physics manuscripts.

4. Develop a knowledge of new features of Medical Physics.
TH‐C‐BRD‐01: Technical and Practical Considerations in Implementing Proton Pencil Beam Scanning
Authors: Clasie B , Bentefour H , Boisseau P , Claereboudt Y , Demaret D , Depauw N , Herrup D , Lu HM , Nett W , Kooy H , Flanz J
Published: April 2010

Purpose: Magnetically scanned proton beams (PBS) have lateral position, energy, spot size, and flux degrees of freedom that allow for optimal target dose distributions and tissue sparing. PBS requires fast and accurate control of the degrees of freedom during the treatment to deliver the desired dose. We describe how a PBS field is delivered and verified in the technology we developed. Methods and Materials: Treatment plan beam parameters are converted to equipment settings, sorted in energy layers, and sent to various measurement and control devices that check the parameters every 0.25 ms. The on‐line dosimetry system was adapted to support this speed and characterized over a range of beam positions and dose rates. These data were calibrated against measurements at isocenter using a variety of instrumentation techniques. Sources of potential error and noise were identified and reduced to a level which enabled accurate clinical treatment. Results: The scanning system produces pencil beams smaller than 6–8 mm lateral width (1σ) with focusing magnets and 9–14 mm without. Dose accuracy is +/−0.2 cGy in the Bragg peak for a single pencil‐beam and +/−0.75% for our reference irradiation geometry. Measured 3‐dimensional dose distributions satisfy the (3 mm, 3%) gamma index criterion with 97% of points below 1. Conclusion: Our current system has proven to be accurate and safe. We developed the capability for treating large tumors, a purpose not usually considered for proton beam scanning but which we see as an important opportunity. We achieved clinically useful dose distributions with our beam and system parameters (including dose and position accuracy and spot size). Further refinements are planned.
TH‐C‐BRD‐02: MU Calculation for Uniform Scanning Proton Beam
Authors: Zhao Q , Wu H , Wolanski M , Hecksel D , Pack D , Das I
Published: April 2010

Purpose: Accuracy in monitor unit (MU) calculation is critical for patient treatment which is measured in proton beam for each field that takes significant of beam time. An accurate, simple and time saving method is desired for MU calculation. Presented is a sector integration approach with constant correction for dose/MU calculation for any treatment in a uniform scanning proton beam. Materials and methods: Dose measurements were made in a scanning proton beam with a parallel plate Markus ion‐chamber in a water phantom. Two methods were adopted to measure the Dose/MU values: (i) varying beam energy and SOBP values with a fixed aperture radius (10cm) at the reference point and (ii) varying the beam energy and aperture radius with a fixed SOBP. These measured values were summarized into two tables. These two tables were used to calculate dose/MU for an energy and a SOBP using certain aperture radius by linear interpolation, which produced the initial results: D(energy, SOBP)10cm and D(energy, radius)SOBP'. The dose/MU value for any field size and shape is calculated using sector integration method with a piecewise correction based on these two values. Results: Dose/MU values for total 412 beam fields without compensators were measured and calculated using the model above. The model parameters were derived from the measurements in 90 fields with varying shapes. These parameters were applied to compute the dose in the other 322 treatment fields. The difference between calculated and measured values in these 322 fields is −0.12%±1.36% for beam range in water <20 cm. The difference is smaller to −0.06%±0.74% for beam range >20cm. Conclusion: An accurate, simple, and fast method for MU calculation in any proton treatment fields is introduced. The sector integration method derived from the actual measured data produced very small error when tested in 322 additional fields.
TH‐C‐BRD‐04: Impact of Various Lung Volumes On Radiotherapy Planning of Lung Cancer
Authors: Gopan E , Glide‐Hurst C , Yan D
Published: April 2010

Purpose: Dose volume histogram (DVH) parameters of the lung have been reported to be risk factors for radiation pneumonitis. We evaluated different lung volumes using 4DCTs to determine the optimal data sets for lung contouring and to develop a model to convert the DVH parameters between datasets. Methods and Materials: A retrospective analysis was performed on 10 patients' 4DCT and fast helical free breathing scans. The lungs were automatically contoured on the averaged (AVG_CT), end expiration (EE), end inspiration (EI), free breathing (FB), maximum intensity projection (MIP) and mean position (MP) images. Volumes and centers of mass were compared to those obtained with deformable image registration (AVG_def). AVG_def contours were created by averaging displacement vectors for each image pixel over the 4DCT, representing the averaged contour due to organ motion. To compare DVH parameters (V20, V12.5 and MLD), patients' plans were standardized as hypo‐fractionated. A population‐based model was tested for converting DVH parameters between datasets. Results: A paired Student's t‐test showed significant variation between AVG_def and other volumes. MP image volume was most statistically similar (0.479%). Centers of mass between image volumes showed little relevant variation. Marked volume effect was observed for dose‐volume relationships. MP image DVH parameters were most statistically similar to those of the AVG_def (< 1%). An average percentage change of 3.95% was observed between V20 of EI and AVG_def volumes. A model to convert from one DVH parameter to another was effective when comparing different volumes. Conclusion: There was a marked variation between the volumes and DVH parameters obtained from EI, MIP and EE images and those of AVG_def. The most statistically similar image, in terms of volume and DVH analysis, was the MP. A model can be used, with caution, in converting the DVH parameters from one image to another.
TH‐C‐BRD‐06: Analysis of the Mechanical Accuracy of Volumetric Modulated Arc Therapy (VMAT) Deliveries and Corresponding Dosimetric Effects
Authors: Matuszak M , DeCesare S , Gersten D , Yan D
Published: April 2010

Purpose: Due to the continuous nature of VMAT deliveries, monitoring mechanical parameters and their effect on dosimetry is not straightforward. The purpose of this work is to present and evaluate a tool that compares real‐time VMAT delivery parameters with expected values, and utilize the tool to evaluate the mechanical accuracy of VMAT plans and judge the effect of mechanical errors on dosimetric QA. Method and Materials: An application was designed to record real‐time VMAT delivery information such as gantry position, leaf positions, and dose rate. An analysis utility was created to compare the delivery data to the DICOM‐RT plan data. Several example and clinical plans with and without simulated errors were delivered to a cylindrical QA phantom and analyzed. Results: For test plans where a 2cm MLC gap oscillated during arc delivery at various speeds, mechanical accuracy was good. The leaf gap absolute error was 0.24+/−0.26mm at maximum speed. For four clinical plans, the average mean gantry/leaf errors were 0.18 °/− 0.01mm and the average standard deviations were 0.35°/0.52mm. The analysis program correctly reported simulated errors in both test and clinical plans, including a 2mm shift of one leaf, a missing control point, and gantry lag. Dosimetric results were not significantly affected by the simulated errors, but the phantom was sensitive enough to detect them. Conclusion: Software tools that support monitoring and subsequent analysis of treatment machine parameters during VMAT compared to expected values have been developed. Clinical plans demonstrated good mechanical accuracy, and simulated errors were detected by the analysis software although dosimetric QA was relatively insensitive to them. These tools can complement VMAT dosimetric QA by helping determine the cause of dosimetric discrepancies, and routine use may also identify potential problems before they lead to dosimetric or other issues.

Conflict of Interest: Supported in part by Elekta
TH‐C‐BRD‐08: The Effect of Embolization Glue On Gamma Knife Radiosurgery of Arterio‐Venous Malformations
Authors: Mamalui‐Hunter M , Jiang T , Derdeyn C , Low D , Drzymala R
Published: April 2010

Purpose: Gamma Knife stereotactic radiosurgery in combination with embolization or alone is a widely recommended treatment option for patients with arterio‐venous malformations (AVM) with estimated near 90% cure rate. A recently published report suggested that the failures to obliterate the AVM nidus were caused by up to 15% dose reduction in the target volume due to the effect of the embolization materials used prior to the Gamma Knife radiosurgery. This work aimed to resolve the issue. Method and Materials: 1) The apparent linear attenuation coefficients for 120keV to 140keV x‐rays in the embolized regions were retrieved from CT scans for several patients with AVM malformations. Based on these coefficients and our virtual model of Gamma Knife with basic ray tracing, we obtained the pathlengths and densities for the embolized regions. The attenuation of Co‐60 beams was then calculated for various sizes and positions of AVM embolized regions and the number of beams used for treatment. 2) Published experiments for several high atomic number materials were used to estimate the effective Co‐60 beam attenuation coefficients for N‐butylcyanoacrylate (doped with high Z) and Onyx (ethylene‐vinyl alcohol copolymer doped with tantalum) used in the AVM embolizations. The dose reduction during Gamma Knife radiosurgery was calculated based on the Co‐60 energy attenuation coefficient. Results: Based on apparent CT (keV) attenuation coefficients, one may conclude that the cumulative effect of the glue would decrease the dose delivered in Gamma Knife radiosurgery from −8 to −15 %. However, using the true attenuation coefficient for Co‐60 energies in the dose calculation leads one to conclude that there is 0.2% dose reduction per beam and less than 0.01–0.2% dose reduction in total. Conclusion: Dose reduction due to attenuation of the Co‐60 beam by the AVM embolization glue material is negligible.
TH‐C‐BRB‐01: Society‐Based Practice Quality Improvement Projects for Maintenance of Certification
Authors: Taylor M
Published: April 2010

Practice Quality Improvement (PQI) is the final component of Maintenance of Certification (MOC) as required by the American Board of Radiology (ABR) and the American Board of Medical Specialties (ABMS). The first three components of MOC: professional standing, lifelong learning and self‐assessment, and the cognitive exam are less ambiguous than the fourth component, PQI, which is meant to provide a pathway for diplomates to critically self‐assess and improve clinical aspects of practice. The PQI process consists of six general steps: select a project and develop metrics, collect baseline data, review and analyze baseline data, implement an improvement plan, re‐measure baseline data, and report participation to the ABR. There are two types of projects that meet the ABR/ABMS requirements: Type I, which are individually‐based projects, developed and attested to by the dipomate; and Type II, which are an ABR endorsed, society‐provided template. AAPM Task Group 127 (MOC) has developed a Type II template that has been submitted to the ABR for endorsement.

Learning Objectives:

1. Understand the steps required to successfully meet the PQI requirements of MOC.

2. Understand the differences between the two types of PQI projects and their essential components.

3. Review and understand the ABR submitted Type II template developed by TG‐127.
TH‐C‐BRC‐01: Precision Localized Radiation to Ablate Progenitor Cells in the Mouse Brain
Authors: Ford E , Achanta P , Armour M , Reyes J , Kleinberg L , Quinones‐Hinojosa A
Published: April 2010

Purpose: Neural stem cells in the adult brain participate in both the repair of normal tissue and inhibition of tumor growth. Here we investigate the effects of localized irradiation on neural stem cells in the rodent subventricular zone (SVZ) emplying a novel device to precisely localize this stem cell niche. Method and Materials: We selectively targeted the SVZ of the mouse using a precision CT‐guided radiation device developed in our laboratory. We delivered 10 Gy to the right SVZ through a 3 mm field (n=4). The left SVZ serves as its own control, but sham mice were also employed (n=4). Mice were sacrificed 7 days after irradiation and brain tissue was harvested, fixed, frozen and sectioned. Immunohistochemical staining was performed for H2Ax, a marker of DNA double strand breaks, and Ki67, a marker of cell proliferation in this neurogenic region. Results: H2Ax stains indicated that the right lateral ventricle was specifically irradiated. A strong asymmetry was observed in the right (irradiated) vs. left (unirradiated) SVZ with 14,106±626 vs. 2,323±1094 cells (p<0.001). The data also showed that the unirradiated (left) SVZ has the same number of Ki67+ cells as a sham mouse (p=0.27) indicating that local irradiation produces no systemic effect under these conditions. Conclusion: Localized irradiation is capable of selectively ablating proliferating cells in neurogenic regions of the mouse brain. This local dose response as well as the irradiating device can be used to study locoregional effects and migration of neural stem cells.
TH‐C‐BRC‐02: Lung Injury From Stereotactic Radiosurgery and Efficacy of Amifostine: A Small Animal Study On Helical TomoTherapy
Authors: Sheng K , Mata J , Cai J , Larner J , Read P
Published: April 2010

Purpose: To evaluate a Helical TomoTherapy‐based rodent radiosurgery platform that reproduces human image guided radiosurgery treatment and to study radiobiologic effects of stereotactic radiosurgery on lung tissues, with or without Amifostine, a radioprotector. Methods and Materials: Hypofractionated radiosurgery with varying radiation dose from 21 Gy to 60 Gy was delivered to the right lung of 16 anesthetized New Zealand rabbits using Helical TomoTherapy in three fractions with MVCT image guidance. Contrast enhanced MR perfusion, hyperpolarized helium‐3 MR ventilation, and CT were obtained before radiation and monthly for 4 months after radiation. The radiological findings were verified by subsequent histopathology studies. Amifostine was given to a subgroup of rabbits received 33 Gy before each fraction of radiation. Results: Precise dose delivery to a 1.6 cc of the lower right lung was achieved without additional immobilization. No deficits were detected at baseline with respect to perfusion and ventilation. Lung perfusion deficits in the irradiated lung regions began at 2 months post radiation and worsen with time for rabbits received 27 Gy and higher. No ventilation defects were observed after radiation. Decrease of lung CT density in irradiated regions was observed after radiation, but the changes were less significant than those in MR perfusion. Compared with rabbits received 33 Gy radiation only, rabbits received Amifostine treatments were significantly better protected from lung injury indicated by a 31% higher perfusion level. Conclusions: We demonstrated that highly conformal radiation can be reproducibly delivered to a small volume of rodent lung on a widely available clinical unit. The radiation‐induced lung injury can be detected as early as 2 months after radiation with perfusion MRI. The primary pattern of injury agrees with previously reported endothelial damage to radiosurgical radiation doses. The injury can be effectively reduced by Amifostine, a free radical scavenger.
TH‐C‐BRC‐04: Small Animal Stereotactic Irradiator
Authors: Pidikiti R , Stojadinovic S , Song K , Seliounine S , Speiser M , Saha D , Solberg T
Published: April 2010

Purpose: We have developed an image‐guided small animal stereotactic irradiator capable of high dose rate radiation delivery and high accuracy in target localization in a manner that mimics clinical stereotactic delivery. In this study, we characterized radiation beams for small animal radiosurgery treatment planning. Method and Materials: The irradiator employs a commercial x‐ray device (XRAD 320, Precision X‐Ray, Inc.) with custom made collimation system consisting of a brass collimator holder and variable tungsten alloy collimators with apertures ranging from 1 to 10 mm in diameter. The image guidance system consists of a high resolution x‐ray intensifying screen (Kodak Min‐R2) coupled to a computer‐controlled digital camera. The x‐ray tube is operated at 30 kVp for imaging, and at 250 kVp for therapeutic delivery. To characterize the radiation beams, we measured percent depth dose curves (PDD), off‐axis ratios (OAR) and absolute dose rates for each collimator using radiochromic film (Gafchromic EBT, International Specialty Products, Wayne, NJ) at 19.76 and 24.76 cm source‐to‐surface distance (SSD). Results: For a 5 mm circular collimator, at 19.76 cm SSD, the penumbra, defined as distance between 80% and 20% isodoses, for in‐plane and cross‐plane measurements was 0.7 and 1.1 mm, respectively. For the 5mm collimator, PDD values of 55% and 20% were at depths of 25 and 50 mm respectively, indicating more than adequate penetration for deep seated targets in small animals. Absolute dose rates ranged from 6.7 to 11.6 Gy/min for the 1 to 10 mm collimators at SSD of 19.76 cm. At 24.76 cm SSD, for 5 and 10 mm collimators, measured dose rates were 7.1 and 7.7 Gy/min, respectively. Conclusion: The irradiator offers high dose rates and sharp beam profiles, and has been systematically characterized for a set of source‐to‐surface distances and field sizes relevant for a number of animal experiments already successfully performed.
TH‐C‐BRC‐07: An Investigation of the Effect of Micro‐CT Radiation Dose On Tumor Growth in Mice
Authors: Foster K , Ford N
Published: April 2010

Purpose: This study is designed to determine the impact of longitudinal micro‐CT imaging on tumor growth in mice. Method and Materials: C57BL/6 mice were divided into four groups, a control group and 3 imaging groups. The control group received no imaging while each remaining group underwent a different imaging protocol. Each mouse received an inoculation of 2×10̂5 B16F1 cells (murine melanoma), subcutaneously in the right hind flank. All imaging was performed on a fast volumetric micro‐CT scanner (GE LocusUltra, London, Canada). The three imaging protocols were as follows: 1. ‘Low dose’ ‐ An 8 second scan with tube settings of 80 kVp and 70 mA (∼ 7 cGy entrance dose per scan), 2. ‘Medium dose’ — 30 second scan at 80 kVp and 50 mA (∼ 17 cGy entrance dose per scan) and 3. ‘High dose’ ‐ 50 second scan at 80 kVp and 50 mA (∼27 cGy entrance dose per scan). The imaging was performed four times: once every four days, starting on the fourth day post inoculation. After the final imaging session each tumor was excised, weighed and imaged (to obtain the final tumor volume) and then processed for histology. Final tumor mass and volume are used to evaluated the impact of longitudinal micro‐CT imaging on the tumor growth. Results: Preliminary results have been obtained for n=8 mice per group. An ANOVA test indicates a significant difference in mean final tumor mass (p = 0.049), with the ‘Low dose’ tumors being largest on average. Conclusion: These preliminary results indicate the ‘Low dose’ tumors have a faster growth rate than the tumors in the other groups, however the power of this test is low (β = 0.49). We are currently working to increase the sample size to n = 16, which should yield acceptable power (β ≈ 0.1).
TH‐C‐303A‐02: Clinical Data Evaluation of Fiducial‐Free Spine Tracking for CyberKnife Radiosurgery
Authors: Fu D , Zhang H , Wang H , Wang B , Kuduvalli G , Maurer CR
Published: April 2010

Purpose: To evaluate the accuracy of the Xsight® Spine Tracking (XST) System in the CyberKnife® Robotic Radiosurgery System (Accuray Incorporated, Sunnyvale, CA) using retrospective analysis of clinical data. Method and Materials: The XST System performs patient alignment and frequent intra‐fractional tracking for spine radiosurgery. The 3 translations and 3 rotations of the 3D transformation are computed and used for treatment couch correction in patient setup and radiation beam position compensation during treatment delivery. The XST System eliminates the need for fiducials by using 2D–3D spine registration of two orthogonal X‐ray images and the planning CT image. Analysis was performed using image data acquired for 26 patients previously treated using fiducial tracking. The data consists of a CT image for each patient plus 4,480 X‐ray image pairs acquired during treatment. The cases cover the entire spinal column (3 cervical, 13 thoracic, 7 lumbar and 3 sacrum). Each patient had 4–6 metal fiducials implanted in vertebrae adjacent to the spine lesion being treated. Fiducial and XST tracking were performed for all X‐ray image pairs. The XST transformation errors were calculated by using the fiducial tracking results as the reference gold standard. Results: The error of each translation component is <0.5 mm in 20/26 patients, <1 mm in 25/26 and <1.5 mm in 26/26. The mean 3D translation error is 0.6 mm. The error of each rotation component is <0.5° in 9/26, <1° in 23/26, <1.5° in 25/26 and <2° in 26/26. The mean total rotation error is 0.8°. For 1 patient with >1 mm translation error and 3 patients with >1° rotation error, the fiducials are far from the center of region of interest, which degrades the fiducial tracking accuracy. Conclusion: The XST System robustly tracks all spine regions and accurately computes both translations and rotations.

Research sponsored by Accuray Incorporated.
TH‐C‐303A‐08: Prostate Localization Using Daily Cone‐Beam Computed Tomography Imaging: Assessment of Accuracy Using Similarity Metrics and Observation‐Based Measures
Authors: Kim J , Hammoud R , Pradhan D , Movsas B , Chetty I
Published: April 2010

Purpose: To estimate the accuracy of daily CBCT/CT prostate rigid‐body registrations using different similarity metrics (SM) and observation‐based measures, and to determine the tradeoffs of these methods. Methods and Materials: Daily CBCT images of 29 prostate cancer patients were retrospectively analyzed; 14 patients with calcifications in the prostate (calcification dataset) and 15 patients without calcifications (no‐calcification dataset). Three groups of test registrations were performed. Test1: 70 CT/CBCT pairs in the calcification dataset were registered using 17 SMs and their various parameters (6580 registrations), and compared using the calcification mismatch vector length as an end‐point. Test2: Using the 4 best SMs based on Test1, 75 CBCT/CT pairs from the no‐calcification dataset were registered using visual comparison as the endpoint (300 registrations), i.e. the accuracy of prostate contour overlays on CBCT images were visually ranked. Test3: For the top ranked SM based on the above 2 tests, the registration accuracy was estimated from 356 CBCT/CT registrations from 11 patients in the calcification dataset with and without calcification filtering from registrations. Results: Test1: Incremental‐sign‐correlation (ISC), gradient‐correlation (GC), gradient‐difference (GD), and normalized‐cross‐correlation (NCC) were the SMs with the least vector length errors (μ±σ: 1.6±0.9∼2.9±2.1 mm). Test2: Using visual criteria, 2 of the 3 reviewers ranked GC slightly higher than the other SMs. Test3: Using GC, 96% of registrations (341/356 registrations) showed less than 3 mm error when calcifications were filtered. Corresponding errors were L/R:0.1±0.5 mm, A/P:0.8±1.0 mm, and S/I: 0.5±1.1 mm. Existence of prostate calcifications increased the number of successful registrations to 97%. Conclusion: The estimated <3mm error was approximately 96% (1.1 mm SD) using GC, ISC and GD similarity measures. These measures offer a relatively quick and accurate means of assessing CBCT/CT registrations in the routine clinical setting. User observation is a necessary requirement in the overall QA of the process.
TH‐C‐303A‐09: 4D CT Sorting Based On Patient Internal Anatomy
Authors: Li R , Lewis J , Cervino L , Lawson J , Jiang S
Published: April 2010

Purpose: To obtain a robust 4D CT sorting algorithm based on patient internal anatomy by combining multiple respiratory features and to compare with sorting algorithms based on external surrogates. Method and Materials: A four‐slice GE LightSpeed™ CT scanner was used to acquire the CT data in cine mode and respiratory signals were synchronously recorded by the Varian RPM system for comparison purposes. To generate respiratory signals directly from the axial CT images, five respiratory features have been evaluated, namely, air content, body area, lung volume, conditional mean with threshold and conditional mean with percentile. For each four‐slice couch position, a quantitative measure called spatial coherence was used to select the optimal internal features for generation of respiratory phases for slice sorting, which, along with the sorted CT images were compared with those obtained from RPM, respectively. Results: Patient studies showed that the respiratory signals generated from internal features are similar to RPM signals for patients with regular breathing patterns (average correlation with RPM signals at all couch positions is above 0.92 in 9 out of 10 patients) and result in sorted images with fewer motion artifacts for patients who exhibited relatively irregular breathing patterns. Conclusion: This work demonstrates the feasibility and potential benefits of using internal anatomy for 4D CT sorting in thoracic and abdominal cancer patients. The sorting results are similar to those obtained with RPM signals for regular breathing patterns and better when irregular ones occur. The proposed algorithm is simple and robust, which makes it amenable for clinical implementation. In the future, alternative measures for the quality of respiratory signals may be investigated in the temporal domain, e.g., smoothness. In parallel, other useful respiratory features may be combined easily with existing ones for better accuracy and more robustness.
TH‐C‐303A‐10: Simulation of An In‐Line 6MV Linear Accelerator From Electron Gun to Target
Authors: St. Aubin J , Steciw S , Fallone B
Published: April 2010

Purpose: To report on the development of a comprehensive linear accelerator (linac) model that simulates the electron dynamics from the electron gun to the target. This model was developed to determine the maximum tolerable magnetic field strength that a linac can operate in, so that passive magnetic shielding can be optimized for use in a large scale linac‐MR system which is currently being developed. The design of magnetic shielding is essential for the linac and MR systems to be coupled together making true real‐time adaptive radiotherapy possible. Method and Materials: The finite element method (FEM) was used to solve the radiofrequency (RF) fields within an in‐house designed 6MV in‐line linac waveguide. A Pierce‐type diode electron gun was designed and the emitted electron trajectories were solved using the particle tracking code EGN2w. The injected electron trajectories and solved RF fields then served as inputs into the particle tracking code PARMELA. Benchmarking of the simulation was performed by taking the electron phase space generated at the target, running it through the BEAMnrc and DOSEXYZnrc Monte Carlo algorithms and comparing the simulated dose distributions to measured values at various field sizes and depths. Results: Discrepancies of less than 0.04% were found when comparing the 3D FEM RF fields to the benchmarked program Poisson Superfish while the simulated dose results were found to be within 1% of measurement for the dose profile horns of various field sizes at various depths. Conclusion: A full simulation of an in‐line 6MV linac waveguide from electron gun to target has been benchmarked, showing agreements of the simulated dose distributions to within 1% of measurement. By adding the known magnetic fringe fields from the bi‐planar magnet, the exact extent of electron trajectory deflections can be determined and thus the optimal magnetic shielding can be designed.
TH‐C‐304A‐01: Utilizing Shape Models Composed of Geometric Primitives for Organ Segmentation
Authors: Gering D , Lu W , Ruchala K , Olivera G
Published: April 2010

Purpose: Image segmentation technology can automate the task of contouring organs for radiation treatment planning. A segmentation method using a five‐layer hierarchy, proposed in AAPM 2008, propagates information from the voxel layer up to voxel neighborhoods, then tissues, then organs, and finally organ systems. An improvement to the organ layer is proposed that uses shape models composed of geometric primitives. Method and Materials: The organ layer generally follows a sequence of six steps for each muscle and organ: (1.) Generate an ROI that limits the search space. (2.) Generate a field of candidate tissues within the ROI. (3.) On a slice‐by‐slice basis, recognize the object within the field that best matches expectations. (4.) Fit a geometric shape model to the cross‐section of the object on each slice. (5.) Smooth the shape parameters over all slices. (6.) Refine the object boundary by reconciling shape and image data. Consider how to define the shape model used by the fourth step. Use an ellipse for the bladder, rectum, and penile bulb. For the prostate, use a large circle with its bottom quarter cut off, and two small side‐by‐side circles with radii half that of the large circle lowered into position. For seminal vesicles, use a horizontal ellipse for the caudal‐most centimeter, which then splits into two ellipses that are permitted to tilt and slide laterally and posteriorly. Results: The segmentation method using geometric shape models has been trained and tested on 50 prostatic datasets. Processing time for volumes with roughly 90 slices, and 256×256 pixels per slice, is 40 seconds on a standard PC, without any human interaction. The segmentation results were verified by trained experts and redeemed to be acceptable. Conclusion: Shape models composed from geometric primitives are a useful method of regularizing the segmentation of muscles and organs.

Sponsored by TomoTherapy.
TH‐C‐304A‐02: A Probabilistic Neural Network Using the Haralick Transform to Segment Ribs in Chest Digital Radiographs
Authors: Rosskamm S , Newman F , Miften M
Published: April 2010

Purpose: Segmenting ribs in chest radiographs is the first step toward a system of automated diagnosis in digital radiography (DR) of the lung. Methods: We use a probabilistic neural network (PNN) and selected components of the Haralick transform as a feature vector to train our neural network in this segmentation task. A Haralick transform composed of statistical components is employed as a feature vector where the relevance of each component to the particular task is determined using a simple scatter plot analysis. A training set is generated by randomly selecting pixels around which a 16 by 16 pixel ROI is constructed. This is done for rib and non‐rib regions. The Haralick transform is applied to this window as a feature vector characterizing the window and hence the region. Once the components from the scatter plot analysis are selected, the Haralick transform is applied. The method is automated in that each pixel is interrogated and classified by the PNN. Results: The PNN performs well with 50 training vectors each from rib and non‐rib areas. There are typically 7 relevant Haralick components after scatter plot analysis. We demonstrate the effectiveness of the method with images that show rib segmentation on two different patients using the same Haralick components and PNN. Conclusion: A probabilistic neural network and the Haralick transform have been shown to be effective methods for segmenting the ribs in digital radiographs of the lung. The next phase would consist of morphological operations to turn the extracted rib images into binary images, thereby allowing the ribs to be disregarded in computer assisted diagnosis of lung DRs.
TH‐C‐304A‐03: MVCT Auto‐Contouring for Adpative Radiation Therapy
Authors: Chao M , Moros E , Ratanatharathorn V , Penagaricano J , Yan Y , Xing L , Gardner K , Corry P
Published: April 2010

Purpose: We develop a megavoltage computed tomography (MVCT) auto‐contouring strategy through contour propagation from planning kilovoltage CT to MVCT. Daily pre‐treatment MVCT taken on the Helical Tomotherapy (HT, TomoTherapy, Inc, Madison, WI) can be used to adaptively modify existing treatment plans provided that we have reliable auto‐contouring tool so we may realize and maximize the potential for adaptive therapy using HT. Methods and Materials: The study includes five head‐and‐neck (HN) and five prostate patients. For each case, physicians outline all regions of interest (ROIs) on the planning CT. Daily MVCTs are acquired during patient setup. Scale Invariance Feature Transformation (SIFT), a feature detection algorithm, is used in contour propagation. Distinctive features from the local area of each ROI are automatically detected on input images and their correspondences are established with the SIFT algorithm. Based on the matched pairs, a spline interpolation is used to register the rest of the points and to obtain a deformation field which is used to warp the contours from the planning CT to the MVCT. Special attention is paid to rectum, bladder and tumor, where contours from various input images may differ greatly. Quantitative assessment of the proposed algorithm is also performed using a number of digital phantoms generated with known vector fields. Results: The digital phantom experiments show that the propagation error is within 1.5 mm, establishing the high accuracy of the auto‐contouring method. For clinical cases, the calculation gives a mean error of less than 3mm in HN patients. For prostate patients, the error for prostate is larger than 4mm in some areas and needs physician's editing of the automatically generated contours. Rectal contour error is within 3mm. Conclusions: A reliable contour propagation technique has been developed for MVCT image segmentation, a useful tool to maximize the potential for adaptive therapy using HT.