bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐SAMS‐AUD B‐01: The Good, The Bad and the Ugly — A Regulatory Update
Authors: Fairobent L , Gilley D , Cameron F , McBurney R
Published: July 2008

There have been a number of new NRC orders that impact unescorted access to Category 1 and 2 materials such as gamma knife and blood irradiators. Fingerprinting and FBI background checks must now be done. In addition, 10 C.F.R. Part 35 requires that a preceptor statement be signed by an individual that is an Authorized medical Physicist, Radiation Safety Officer, Authorized User or Authorized Nuclear Pharmacist. Recently the Nuclear Regulatory Commission (NRC) has issued findings against signors of preceptor statement for falsifying information. This session will address the liabilities of medical physicists in signing preceptor states, in serving as the “trustworthy and reliable” official for a license in determining unescorted access. It will address differences in non‐agreement states and agreement states.

Finally, the AAPM has a policy statement that states: in essence to practice medical physics you must have a masters or Ph.D. and be board certified in one of the disciplines of medical physics. There are four states that required licensure of medical physicists for a number of years. The final talk in this session will look at whether or not having licensure has made a difference in the quality of medical physics practiced and the ramifications of the new Part 35 requirements for training and experience.
TH‐C‐AUD C‐01: Lung Mechanical Modeling Based On the 3He MR Tagging and Lobar Segmentation
Authors: Sheng K , Cai J
Published: July 2008

Purpose: Direct measurements of the lung deformation by MR tagging during breathing motion revealed that the deformation is neither linear nor continuous. To improve the accuracy of deformable registration by finite element analysis, the lung is segmented into subanatomical regions, to allow sliding motion between lobes. Method and Materials: One healthy volunteer underwent MR tagging studies. Multiple‐slice two‐dimensional and volumetric three‐dimensional MR tagged images of the lungs were obtained at end‐inhalation and end‐exhalation, and deformation vector field (DVF) was computed. A patient CT was selected and the left lung was segmented into upper and lower lobes. The 2D contours were converted to 3D mesh and subsequently to tetrahedra for finite element analysis (FEA). Boundary conditions and material properties were assigned in the ABAQUS, FEA modeling software. Diaphragm provided the active driving pressure and the chest wall provided a passive constraint. The FEA computed DVF was compared with the measured DVF using a similarity index (SI) normalized to 1 for a perfect match and 0 for a complete mismatch. Results: A 3D lung DVF was generated from the MR tagging. Distinct discontinuity was observed between lung lobes. With the assumption that the lung is a continuous elastic object, the FEA model failed to model the discontinuity along the fissure and resulted in a low SI (0.53), which was improved to 0.89 by segmenting the lung and introducing the additional freedom of inter‐lobar motion. Conclusion: DVF measured from MR tagging can be a reference in validating deformable registration of lung, particularly in regions with low imaging contrast. Using this reference, the authors were able to significantly improve the accuracy of deformable registration with lobar segmentation in the FEA modeling.
TH‐C‐AUD C‐03: Patient Setup Using 2D Projected Images and Setup Error Estimation
Authors: Zhao Q , Wu H , Desrosiers C , Cao M , McMahon R , Thai V , Langer M
Published: July 2008

Purpose: Fiducial markers or bone structure are widely used in patient setup for image guided therapies and is also important in interventional radiology. A general approach (“2D‐2D”) for patient setup is based on 2D projected images on the anterior‐posterior (AP) and lateral (LAT) directions. However, it is still an open question to decide the number of fiducial markers required for patient setup, the optimal locations for marker plantation, the selection of fiducial markers versus bone structure, and the error estimations of different setup methods. Our work will address some of these issues and provide quantified information. Method and Materials: Clinical patient setup procedure (“2D‐2D”) is simulated using rigid registration. Least square metric is applied to minimize the alignment error of markers. Registration under different degree of freedom (DOF) are performed, including 3DOF (translation only), 4DOF (translation and AP couch rotation) and 5DOF (translation and rotation on AP and LAT). Registration errors are calculated based on absolute or percentage of missed volume between estimation tumor location and real tumor location. Results: Patient setup errors were investigated using different registration methods under various tumor motion conditions. The results showed that back and forth shifts using alternating projection planes can worsen the true registration of the target center with each “correction” step given target rotation. Second, for off center rotations of five degrees, no alignment can result in smaller errors than 2D‐2D registrations, despite a true translation of the target center. In addition, a 3DOF alignment process performs better against rotational shifts than both 4DOF and 5DOF that allow rotations within the projection planes. Conclusion: The quantitative analysis and setup error estimation using “2D‐2D” registration will provide better guidance for patient setup, which is important for effective radiation treatment of cancer patients.
TH‐C‐AUD C‐05: Assessment of Intrafractional Motion for Spinal Radiosurgery Patients by Multiple Onboard Megavoltage CT Scans During Treatment
Authors: Duan J , Fiveash J , Shen S , Popple R
Published: July 2008

Purpose: To assess the intrafractional patient motion during single‐fraction spinal radiosurgery using multiple CT scans acquired with onboard megavoltage CT (MVCT) during treatment. Method and Materials: Nineteen patients underwent single‐fraction (12 – 24 Gy) spinal radiosurgery on a TomoTherapy HiArt radiotherapy unit with onboard MVCT. Because of the large fractional dose, the treatment was divided into 3 or more sub‐fractions. Patients were immobilized with BlueBAG™ BodyFIX® except for C‐spine patients who were immobilized with face‐and‐shoulder masks. To accurately align the patient, an initial MVCT was acquired after patient was setup to skin marks. Image registration between MVCT and planning CT was performed using an auto‐registration algorithm followed by manual fine tuning to calculate the couch shifts. Immediately after the alignment, a verification MVCT scan was acquired. The couch was further shifted according to verification CT before the first sub‐fraction was delivered. Subsequently, MVCT was reacquired and the patient realigned after each sub‐fraction. A total of 67 MVCT‐guided intrafrational alignments (excluding initial alignments) were evaluated for the 19 patients. Couch shifts were analyzed to obtain the information of patient intrafractional movements. Results: The mean ± standard deviation for the magnitude (and displacement which is expressed in parentheses) of the shift was 1.0±0.9 mm (0.16±1.31 mm) in the lateral direction, 1.2±1.1 mm (0.31±1.62 mm) in the anteroposterior direction, 1.6±1.2 mm (0.44±1.97 mm) in the superoinferior direction, and 2.5±1.4 for the resultant vector. The respective maximum shifts were 5.0 mm, 5.4 mm, 5.7 mm and 5.9 mm. Majority (73%) of the realignments required shifts less than 3.0 mm. Image resolution and registration errors may have contributed to the observed intrafractional motions. Conclusion: Patient intrafractional motion should be considered in treatment planning for spinal radiosurgery patients. More intensive intrafractional monitoring and better immobilization device are necessary to reduce intrafrational patient motion.
TH‐C‐AUD C‐08: Moving Towards Real Time Adaptive Radiation Therapy: Integrating Patient Imaging, Plan Adaptation and Radiation Delivery
Authors: Mestrovic A , Nichol A , Clark B , Otto K
Published: July 2008

Purpose: To propose a new approach to on‐line adaptive radiation therapy (ART) in which daily image acquisition, plan adaptation and radiation delivery are performed concurrently. Method and Materials: Daily imaging was performed using an on‐board cone beam CT imaging system. X‐ray projections were continuously acquired as the gantry rotates between treatment positions. A filtered back‐projection algorithm was used to reconstruct 3D digital tomosynthesis (DTS) images from the limited angle x‐ray projection data. An edge detection algorithm was used to automatically segment the 3D DTS images as the gantry arrives at each treatment position. The treatment plan was then re‐optimized for the most recent DTS image contours using modified direct aperture optimization (DAO). To test our system, a model representing an average prostate case was generated. A treatment plan based on this original anatomy was created using our DAO system. To simulate inter‐fractional prostate deformations, three clinically relevant deformations (labeled: small, medium and large) were modeled by systematically deforming the original anatomy. The ability of our integrated approach to adapt the original treatment plan to account for the anatomy deformations was investigated. Results: The original treatment plan becomes clinically unacceptable for all three deformations, based on the dose‐volume constraints from the Radiotherapy and Oncology Group 0415 prostate protocol. Using our integrated approach to on‐line ART, the original treatment plan was successfully adapted to arrive at a clinically acceptable plan for all three anatomy deformations, with the treatment time drastically reduced compared to the current on‐line ART procedure. Conclusion: We have developed a new approach to on‐line ART in which image acquisition, plan adaptation and radiation delivery are temporally integrated. We have shown that it can successfully adapt the original treatment plan for three clinically relevant prostate deformations while considerably reducing treatment time.
TH‐C‐351‐04: 18F‐FLT PET Imaging of Proliferative Response to An EGFR Inhibitor in HNSCC Xenograft Mouse Models
Authors: Nyflot M , Grudzinski J , Titz B , Armstrong E , Wheeler D , Harari P , Jeraj R
Published: July 2008

Purpose: Growing interest in targeted cancer therapies requires increasingly sophisticated understanding of response in tumor microenvironments. This work quantifies the proliferative response of two murine xenograft tumor models to an EGFR (epidermal growth factor receptor) inhibitor, cetuximab, using FLT‐PET imaging. Method and Materials: Athymic mice harboring human head and neck squamous cell carcinoma (HNSCC) xenografts were injected with , a proliferation marker, and imaged on an Inveon microPET/CT scanner. MicroPET/CT imaging was performed on days one and five. Mice were then treated with cetuximab on days two and four with appropriate IgG controls. PET values were normalized by injected dose and weight (%ID/g) and evaluated in the tumor region. Results: Inhibition of FLT proliferation signal following cetuximab administration was statistically significant in a paired t‐test. Average FLT uptake in the tumor decreased from to in cetuximab‐treated SCC‐1483 xenografts and from to in cetuximab‐treated SCC‐1 xenografts. Maximum and cumulative FLT uptake showed similar trends. Initial proliferation rates and magnitude of treatment response were greater in the SCC‐1483 cell line. IgG controls did not show a significant change in FLT uptake. Conclusion: This work demonstrates the capability to measure the effect of a molecular inhibitor of EGFR signaling on proliferation within the tumor microenvironment as measured by PET. This technique should improve understanding of tumor response to EGFR inhibitor therapy and may provide a valuable tool to assess early treatment response to cetuximab in humans.
TH‐C‐332‐05: Quantification of Breast Density with Dual Energy Mammography
Authors: Ducote JL , Molloi S
Published: July 2008

Purpose: To investigate a quantitative method for measuring breast density (the percentage of glandular breast tissue) with dual energy mammography using a dual exposure / dual kVp technique. Method and Materials: An analytical simulation model was developed to determine the mean glandular dose required to quantify breast density to within an accuracy of 1%. The simulation considered stochastic x‐ray and detector noise sources in a dual energy breast density image. The breast was modeled as a semicircle 10 cm in radius with homogenous equal thicknesses of adipose and glandular tissues. Monoenergetic beams were simulated with an ideal detector and polyenergetic spectra were simulated with an energy integrating detector modeled after an existing clinical system. A surrogate breast phantom was constructed to simulate a range of breast densities from 0 to 100%. The phantom was imaged using a full field digital mammography system at 25 kVp and 39 kVp with an additional 2 mm Al filter added to the high energy image. Dual energy images were generated with a non linear basis decomposition algorithm to yield image thickness maps of glandular and adipose tissue. Breast density was quantified using the dual energy images. Results: For a 4.2 cm breast of 50% density, optimal energies determined from simulation, for monoenergetic beams and an ideal detector, were 19 keV and 71 keV. For an energy integrating detector and polyenergetic spectra, optimal energies were 20 and 69 kVp. The estimated required dose for either technique was less than 0.1 mGy. For dual energy images, the known (K) and measured (M) breast densities were related by M = 1.007K − 0.006 (r = 0.999). RMS error for all densities was calculated to be less than 2% of the mean density. Conclusion: The results suggest that breast density can be accurately measured with dual energy mammography.
TH‐C‐332‐07: Dual Energy Contrast‐Enhanced Breast Computed Tomography: A Phantom Study
Authors: Le H , Ducote JL , Molloi S
Published: July 2008

Purpose: To investigate lesion enhancement with iodinated contrast material using dual energy breast computed tomography (CT). Method and Materials: The dual energy cone‐beam breast CT system consisted of a flat panel detector and an x‐ray tube installed on an optical bench. The x‐ray tube voltage and x‐ray beam filtration were switched at 30 Hz between 50 kVp (2.0‐mm Al filter) and 120 kVp (2.0‐mm Al + 0.8‐mm Ag filtration). A cylindrical breast phantom was constructed from polymethylmethacrylate (PMMA) and filled with oil and shredded PMMA. Five known concentrations of iodine (0.5, 1, 2, 4, 8 mgI/ml) were embedded in the phantom. The images were reconstructed with a Feldkamp filtered‐back‐projection algorithm. Dual energy subtraction was used to eliminate the contrast of oil and PMMA to enhance iodine signals. Results: The low energy scan could not distinguish PMMA and iodine concentrations of 0.5 and 1 mgI/ml. The high energy image could not distinguish PMMA and iodine concentration of 8 mgI/ml. After subtracting the PMMA, all five concentrations of iodine could be clearly visualized on the dual energy CT image. The dual energy iodine signal (CTDE) and the iodine concentration (CI) were related by (R = 0.998 and SEE=15.26) Conclusion: Dual energy contrast‐enhanced breast CT can potentially improve lesion.
TH‐C‐332‐08: Calibration of the Geometry in a Stationary Digital Breast Tomosynthesis System
Authors: Rajaram R , Yang G , Lee YZ , Lalush D , Lu J , Zhou O
Published: July 2008

Purpose: To accurately estimate the parameters those describe the geometry of a stationary digital breast tomosynthesis system, namely, the source‐detector distance and the location of the focal spots. Method and Materials: Our novel stationary tomosynthesis system consists of 25 x‐ray sources linearly arranged to cover an angle of 48°. With a limited number of images, the tomosynthesis reconstruction becomes very sensitive to geometric alignment. It is vital that we accurately calibrate the geometry of the system with a suitable phantom. We have designed and built such a phantom that consists of two 6 mm stainless steel balls mounted on a low‐density plastic base. We obtained twelve evenly spaced projection images of the phantom over 360° for each x‐ray source. The motion of the two objects in a circle during data acquisition will cause their projections to trace ellipses on the detector. We calculated the centroids of the two objects in the detector plane and used these to derive the ellipse parameters. Together with the known distance between the two objects, this enabled us to analytically solve for the geometry parameters. Results: The source‐detector distance was calculated to be 69.4 ± 2 mm. The calculated distances between the sources were also in good agreement with the designed values. The parameters were used for the tomosynthesis reconstruction of a sponge phantom and the results showed improved image quality and geometric accuracy. Conclusion: We have designed and tested a calibration phantom that can accurately estimate the geometry of a stationary tomosynthesis system. We are continuing to assess the accuracy of our method to optimize our results. Further, we are looking at ways in which to make the process more efficient by calibrating for only the central source using this phantom and estimating the locations of the other sources using a simpler secondary phantom.
TH‐C‐352‐03: Introduction and Clinical Use of Electronic Brachytherapy
Authors: Hiatt J
Published: July 2008

Electronic Brachytherapy (EBT) is internal radiation therapy that involves placing a miniature x‐ray source inside the patient close to or in the tumor. Recently, one EBT system (Axxent, Xoft Inc., Fremont, CA) has been released for clinical use. Because of its novelty, EBT has been relatively unstudied thus far in the clinical setting and is consequently unfamiliar to many medical physicists. The EBT modality offers several advantages over the Ir‐192 standard of care HDR brachytherapy source. Because of the relatively low energy of the EBT device (50 kV), treatments can be delivered in an unshielded room in contrast to the shielding required for HDR brachytherapy. The low external exposure rate also allows staff to remain near the treatment couch during dose delivery, offering the opportunity to provide comfort and encouragement in close proximity to the patient.

As yet, recommendations for the commissioning of an EBT system have not been officially drafted. However, commissioning an EBT system should include tests of well‐chamber constancy, beam stability, source positional accuracy, output stability, timer linearity, dummy marker/source position coincidence, controller functionality and safety interlocks and treatment planning data verification following AAPM TG43 recommendations.

Early EBT systems focused on treatment of the breast, using an intracavitary balloon catheter surgically implanted in a lumpectomy excision cavity. In comparison to Ir‐192, the EBT treatment results in a higher dose on the applicator surface, an equivalent distribution over the target region and a lower dose to normal structures around the implant area. Recent FDA clearances will allow the extension of EBT to additional sites, including endometrial applications.

This lecture will provide an overview of EBT, a commissioning procedure, and examples of its clinical use.

Educational Objectives:

1. Gain basic knowledge of EBT as a potential HDR‐alternative treatment modality.

2. Understand a proposed commissioning protocol for an EBT system.

3. Learn about the current clinical uses for EBT.

Conflict of Interest: Partial financial support was provided by Xoft, Inc.
TH‐D‐350‐01: Time and Manpower Requirements for Clinical Commissioning of the Passively Scattered Proton Beams at PTC‐H
Authors: Gillin M , Zhu X , Sahoo N , Lii M , Arjomandy B
Published: July 2008

Purpose: To present major tasks and staffing for the clinical commissioning of the passively scattered proton beams at the Proton Therapy Center — Houston. Method and Materials: PTC‐H is designed to be a phased project with the large field passively scattered beams delivered in early phases. At the completion of acceptance testing, clinical physics began the commissioning. Each of the three beamlines has three snouts and eight energies. Major commissioning tasks included SOBP measurements to define the gating off tables, pristine Bragg Peak measurements and beam profile measurements as required for input to the planning system, validation of planning system output, and point dose measurements to define relative output factors for the different treatment delivery parameters. The PTW MP3 system was used for beam scanning, configured for four seconds per data point. Results: Approximately two years were required from the beginning of commissioning to the final initial measurements, taken on the small snout. After the first three months, patient treatments began. The majority of clinical commissioning occurred on Saturdays. Two to three clinical physicists made measurements, while another two physicists focused on the planning system. Approximately twelve hours of in room time were required for each of the 24 options with 2 hours to measure gating off SOBPs, 3 hours for planning system input data, 4 hours of planning system validation data, and 3 hours for point dose dosimetry factors. Additional time was devoted to spot checking other beamlines for confirmation that dosimetry characteristics are identical. Approximately fours were spent per option to prepare and enter data into the planning system. Conclusion: A limited number of clinical physicists can commission passively scattered proton beams in a phased manner, while patient treatments are also being delivered.
TH‐D‐350‐02: Implementation of An Electronic IMRT QA Process in a Network Comprised of Independent Treatment Planning, R&V, and Delivery Systems
Authors: Kumaraswamy L , Podgorsak M
Published: July 2008

Purpose: The purpose of our study is to implement an electronic method to perform and analyze IMRT QA using the ASi imager in a network comprised of independent treatment planning, R&V, and delivery systems. Method and Materials: A verification plan was generated in the treatment planning system using the actual treatment plan of a patient. After exporting the treatment fields to the R&V system, the fields were delivered in the QA mode with the ASi imager deployed. The resulting dosimetric images are automatically stored in a DicomRT format in the treatment console PC. The grey scale images are subsequently pushed to the R&V system. The measured images are then transferred electronically to the planning system and imported into the QA plan in the dosimetry work space for further analysis. The screen shots of the gamma evaluation and isodose comparison are imported into the R&V system as a word document to be reviewed prior to initiation of patient treatment. The calculated images can also be sent as a grey scale image to the R&V system to be compared with the measured dose represented as a gray scale image. Results/Discussion: Our department does not have an integrated planning, R&V, and delivery system. In spite of this, we are able to fully integrate a paperless and filmless IMRT QA mechanism. This process enables the QA process to be more efficient and the QA document can be directly attached electronically to its specific patient chart in the R&V system. The calculated and the measured grey scale images can be viewed electronically side by side to analyze the density differences and ensure proper dose delivery to patients. Conclusion: In the absence of an integrated planning, verifying, and delivery system, we have shown that it is nonetheless possible to develop a completely electronic IMRT QA process.
TH‐D‐350‐04: A Structured Approach to Constructing a Radiation Oncology Physics Residency Program
Authors: Boyer A , Bourland P , Mistry V , Shoales J , Fang B , Montanaro P , Stumph K , Jones D , Tang W , Coker A , Oas L
Published: July 2008

Purpose: This paper describes systematic choices and their rationale for structuring a curriculum for a Radiation Oncology Physics Residency accreditable by the Commission on Accreditation of Medical Physics Education Programs (CAMPEP). Method and Materials: The AAPM Report No. 90, “Essentials and Guidelines for Hospital‐based Medical Physics Residency Training Programs” lists ten rotation topics related to routine clinical treatment planning and delivery procedures and processes and the technical support and quality assurance that support them. The procedures implemented in a specific radiotherapy department depend upon the equipment and software purchased by the facility as well as the individual preferences of the radiation oncologists and staff of the department. Specific procedures and processes appropriate for the rotation categories were identified and listed. However, an approach to developing a Resident's competency performing the processes can be generalized into three phases. In Phase I the Resident observes a Mentor carry out the process and reads background material. In Phase II the Resident carries out the process under close supervision by the Mentor. In Phase III the Resident carries out the process independently. The Mentor documents satisfactory completion of each phase. The Assessment of the Resident's competency is completed by oral examinations by the Residency Program Faculty. Results: The approach was applied to writing a Self‐Study Document for CAMPEP. The document contained a detailed description of ten competency‐based rotations using the three phase format. The descriptions of the rotations composed the majority of the 233‐page study. Conclusion: A Radiation Oncology Physics Residency Program can be systematically constructed by identifying processes and procedures associated with AAPM Report No. 90 competencies and then developing the Resident's competencies with these processes and procedures in three phases. Conflict of Interest : This work supported in part by a grant from the American Society of Therapeutic Radiology and Oncology.
TH‐D‐350‐06: A Web Based Physics Teaching File for Radiology Residents
Authors: Ogden K , Seibert J , Huda W
Published: July 2008

Purpose: To describe a web‐based digital teaching file of imaging physics for Radiology residents. Method and Materials: The RSNA R&E Foundation supported the development of a web‐based physics teaching file for Radiology residents. This RSNA Physics Teaching File was completed at the end of 2007 and is freely available to any computer with internet access. Modalities that employ x‐rays in the image formation process are described, including radiography, mammography, fluoroscopy, angiography, and computed tomography. There are also sections on general characteristics of digital images and image processing, which has become ubiquitous in digital imaging. Results: The website is hosted at SUNY Upstate Medical University and may be viewed at http://www.upstate.edu/radiology/rsna. Each section contains digital images generated with appropriate phantoms on the various modalities, as well as a selection of clinical images. Illustrated are important technical issues related to image quality (i.e. contrast, resolution, and noise) and how these are affected by parameters associated with image acquisition. Effect of changing tube voltage, tube current, field of view, image matrix size, and scatter reduction techniques are illustrated. Special sections were included to explain dual‐energy imaging and other image processing techniques in radiography. Conclusion: The teaching file web site is a valuable resource for teaching the physics of x‐ray imaging to radiology residents.
TH‐D‐350‐07: A 15 Year History of the First Accredited Physics Residency Program: Lessons Learned
Authors: Klein E , Low D
Published: July 2008

Purpose: When the AAPM Report Number 36, “Guidelines for Residency Programs”, was published our institution created a program in Radiation Oncology. This report summarizes our 15 year history. Method and Materials: In 1993, our institution formalized our training approach and established Radiation Oncology Physics Residencies. In 1997, the program became the first accredited by CAMPEP. The program was re‐accredited in 2003. Over time we've tried to improve our program and modernize as technologies advance. We've tracked administrative aspects, particularly, the success of our graduates in terms of employment and board certification, and our applicant pool's background. Results: For the 27 individuals that have entered our program, 12 had been post‐doctoral fellows, 6 had graduated non‐CAMPEP programs, 4 graduated from CAMPEP accredited programs, and 4 had established careers. Twenty physicists have graduated (15 PhD, 15 MS), two failed to complete the program, and one departed due to medical issues. Of the graduates, 14 are at academic facilities and 6 are in non‐academic practice. Every graduate that has taken the ABR/ABMP exam, written and oral have passed at every stage on their1st attempt. Over the past 5 years, there have been 352 applicants for the position(s) that were available. Of these, 49% have been newly graduating physicists with only a small minority (9% of total applicants) graduating from CAMPEP‐accredited programs. Of the applicants 1/3 held post‐docs, 12% were established in a career, and 6% were from overseas. Some changes we've made over the years have been to establish more customized and advanced rotations (i.e. IMRT, IGRT) and to increase testing frequency. Conclusion: The majority of applicants have come from non‐CAMPEP accredited graduate programs, while we have primarily accepted and graduated applicants with post doctoral backgrounds. Our program is sufficiently dynamic to adapt to technological advancements and undergo continuous improvement.
SU‐GG‐J‐56: Comparison of Shifts in CBCT and Tomotherapy Imaging Modalities in Prostate IGRT
Authors: Chen C , Trierweiler K , Bichay T
Published: July 2008

Purpose: Dose conformality in radiation therapy continues to improve with more sophisticated treatment planning algorithms. This trend has further increased the importance of IGRT to ensure the dose is deposited as intended. This study compares the magnitude of shifts in prostate IGRT as measured by two imaging modes: Siemens MV‐CBCT and TomoTherapy helical MVCT. Method and Materials: A total of 18 patients with implanted prostate markers were studied. Patients were treated either by step‐and‐ shoot IMRT on a Siemens's linac or on a TomoTherapy unit. Prior to each treatment, MVCT was acquired and registered with KVCT based on three implanted gold markers. Lateral, longitudinal and vertical shifts were determined. A total of 173 daily localizations from CBCT and 425 daily localizations from helical MVCT were collected. In both cases, image fusion was carried out by the same group of therapists. The data was analyzed retrospectively. Results: CBCT data: The lateral shifts range from 17mm left to 5mm right; the longitudinal shifts range from 16mm superiorly to 6mm inferiorly; the vertical shifts range from 14mm anteriorly to 15mm posteriorly. The mean shift in 3D is 7.7mm. Helical TomoTherapy data: The lateral shifts range from 10.2mm left to 20.6mm right; the longitudinal shifts range from 10.8mm superiorly to 13.1mm inferiorly; the vertical shifts range from 25.7mm anteriorly to 11.1mm posteriorly. The mean shift in 3D is 9.01mm. Conclusion: The results of the two IGRT imaging modalities demonstrate a similarity in the magnitude of daily shifts required for patients undergoing IMRT for prostate. The shifts are significant and would result in target underdosing, or normal tissue overdosing, when not applied.
Poster — Thurs Eve‐41: Imaging and radiation delivery in helical tomotherapy: Phantom study of a moving target
Authors: Gallagher C , Yartsev S , Van Dyk J
Published: July 2008

Treating lung cancer with radiation therapy by guaranteed delivery of the prescription dose to the target is difficult due to tumour motion. The standard approach to account for motion effects consists of adding a substantial margin to a lesion visible on the CT study. Larger irradiated volume results in increased dose deposition in healthy lung and the potential for patient complications. This investigation focuses on determining the optimal choice of planning CT mode for improved radiation delivery in terms of better target coverage and sparing of healthy organs. Dosimetric measurements were performed on a helical tomotherapy unit. A Quasar® (Modus Medical Devices, London, ON) respiratory phantom was imaged while a polystyrene target moved sinusoidally with a period of 4 s and amplitude of 2 cm. For target moving in superior‐inferior and lateral directions, conventional fast‐CT image studies were created, as well as maximum intensity projection (MIP) and average intensity projection (AveIP) image studies using four‐dimensional CT information. All types of CT studies were used to develop treatment plans with a prescription of 2 Gy per fraction to the target outlined according to the imaged data. Measurements of dose deposition were made in four locations within the moving target using an Exradin A1SL ion chamber. Comparing all results to the dose measured at the centre of the static phantom, the MIP plans overdose the target, the fast‐CT results vary from case to case, while the AveIP plans provide consistent dose distribution across the target within 2% of the normalization dose.
Poster — Thurs Eve‐42: A revision of the γ‐evaluation: Initial interpretation of dose disagreements on γ‐vector fields
Authors: Holmes O , Darko J , Dhanesar S , Olding T , Schreiner LJ
Published: July 2008

Gamma evaluations are a common clinical tool used as a quantitative comparison between dose‐distributions, combining both dose difference and distance to agreement criteria. Because gamma evaluations permit rapid analysis of agreement between complex dose distributions, they are often a preferred comparison method for assessing delivery of conformal radiotherapy distributions. Although the comparison provides a useful measure of agreement between distributions when the index is less than one, the scalar gamma value provides little information into the clinical significance or source of disagreements of failing gamma values (i.e., when γ>1). Previously, Stock et al., have presented the gamma angle as an indicator of the relative influence of the distance to agreement versus the dose difference on gamma. We present a modification to the gamma evaluation such that the complete 3D gamma vector information is considered. The predictive nature of each vector component was investigated by simulating various dose disagreements in test distributions. Misalignment tests revealed that the mean gamma vector components indicate the offset direction and relative magnitude for all test distributions. The mean dose component of the gamma vector was prognostic of double Gaussian overdoses and underdoses in a virtual conformal delivery. The response of the vector field depends on properties distinctive to each distribution, such as the local dose gradient. Understanding how these unique properties affect the vector field may permit better diagnosis of dose disagreement sources. Other vector field properties, such as curl and divergence, may yet provide more information for interpreting the cause and significance of γ>1.
Sci‐Fri AM: YIS‐07: A new paradigm for improving IMRT: Selection of beam orientations by optimizing beam intersection volume
Authors: Potrebko P , McCurdy B
Published: July 2008

A beam orientation optimization (BOO) algorithm based on optimizing beam intersection volume (BIV) components within an Organ‐at‐Risk (OAR) is proposed to improve conventional intensity‐modulated radiation therapy (IMRT). A simulated annealing algorithm was employed to search for the optimal set of five beam orientations (5‐opt) which simultaneously minimize the BIV components within an OAR. The 5‐opt plans were compared to standard 5, 7, and 9 equiangular‐spaced beam plans (5‐equi, 7‐equi, 9‐equi) for: (1) gastric (2) Radiation Therapy Oncology Group (RTOG) P‐0126 prostate and (3) RTOG H‐0022 oropharyngeal (Stage‐III, IV) cancer patients. In the gastric case, the coplanar 5‐opt plan reduced the right kidney V 20 Gy by 41.1%, 32.1%, and 29.5% compared to the 5‐equi, 7‐equi, and 9‐equi plans. In the prostate case, the coplanar 5‐opt plan improved rectal sparing over all standard plans with a reduction of the V 75 Gy, V 70 Gy, V 65 Gy, and V 60 Gy of 3.9%, 6.2%, 8.1%, and 10.6% compared to the 5‐equi plan. In both oropharyngeal cases, the non‐coplanar 5‐opt plan substantially reduced the V 30 Gy and mean dose to the contralateral parotid compared to the 5‐equi, 7‐equi, and 9‐equi plans: (Stage‐III) 8.9%, 7.0%, 8.6% and 4.1 Gy, 2.5 Gy, 2.7 Gy (Stage‐IV) 11.2%, 11.2%, 10.8% and 7.8 Gy, 7.9 Gy, 8.0 Gy. In conclusion, the method of optimizing BIV to produce substantial improvements in OAR sparing over conventional IMRT has been demonstrated to be robust for application to a variety of IMRT treatment sites.
Sci‐Fri PM: Planning‐02: MRI‐based radiation treatment planning for an MRI‐linac system
Authors: Stanescu T , Kirkby C , Jans H , Wachowicz K , Rathee S , Carlone M , Murray B , Fallone G
Published: July 2008

At Cross Cancer Institute, we are investigating a novel MRI‐linac system consisting of a bi‐planar 0.2 T permanent magnet coupled with a 6 MV Linac. The system can freely revolve axially around the patient to deliver dose from any desired angle. For such a system, the radiation treatment planning procedure is expected to rely on the MR images only, i.e. MRI Simulation. Replacing the current CT/CT+MRI‐based RTP procedure with MRI Simulation will eliminate the need for the planning CT scanning sessions (no additional x‐ray exposure) and consequently the image fusion between MRI and planning CT. In this work, we propose a comprehensive MRI‐based RTP procedure for an MRI‐Linac system. Specifically, the method consists of a) data acquisition, b) analysis and correction of image artifacts caused by the scanner‐related and patient‐induced distortions, c) segmentation of organ structures relevant to dosimetric calculations (e.g. soft tissue, bone, air), d) conversion of MR images into CT‐like images by assigning bulk electron density values to organ contours defined at step c), e) dose calculations in external magnetic field, and f) plan evaluation. Monte Carlo simulations were performed to determine the linac‐MRI scanner's magnetic field induced effects on the dose deposited patterns using patient data. Specifically, we investigated the dosimetric differences between the corresponding MRI‐based RT plans simulated at zero and 0.2 T. We found that the maximum percent differences for brain studies were within 4%. Most of these differences occurred at the inferior field edge and superficially at beam exits.
Sci‐Sat AM(2): Brachy‐03: Monte Carlo dosimetry for I‐125 and Pd‐103 eye plaque brachytherapy
Authors: Thomson RM , Taylor REP , Rogers DWO
Published: July 2008

A Monte Carlo study of dosimetry for eye plaque brachytherapy was performed. BrachyDose, an EGSnrc user‐code which makes use of Yegin's multi‐geometry package, was used to fully model Iodine‐125 (model 6711) and Palladium‐103 (model 200) brachytherapy seeds and the standardized plaques of the Collaborative Ocular Melanoma Study (COMS). Three‐dimensional dose distributions in the eye region were obtained. In general, dose to water was scored, however the implications of replacing water with eye materials was explored. The effect of the gold alloy (Modulay) backing was investigated and the dose was found to be sensitive to the elemental composition of the backing. The presence of the silicon polymer (Silastic) seed carrier resulted in substantial dose decreases relative to water, particularly for Pd‐103. For the Modulay backing and Silastic insert combination in a 20 mm plaque, the dose decrease relative to water is of the order of 12% for I‐125 and 20% for Pd‐103 at a distance of 1 cm from the central seed along the plaque's central axis. For the configurations of seeds used in COMS plaques, interseed attenuation is a small effect within the eye region. The introduction of an air interface results in a dose reduction in its vicinity which depends on the plaque's position within the eye and the source type. The dose distributions in the eye for the two different sources were compared and, for the same prescription dose, Pd‐103 generally offers a lower dose to critical normal structures.
Sci‐Sat AM(2): Brachy‐04: Spectral and dosimetric study of the Xoft electronic brachytherapy system
Authors: Liu D , Reniers B , Poon E , Bazalova M , Rusch T , Verhaegen F
Published: July 2008

The Axxent developed by Xoft Inc. is a miniature x‐ray tube capable of generating a 50 kVp x‐ray spectrum with dose‐rates suitable for HDR applications. Results of spectral measurements compared with Geant4 Monte Carlo simulations have been published. This study is a continuation of previous work with shifting emphasis towards dosimetric characterization of the miniature x‐ray tube. Dose distributions using EBT Gafchromic films agree to within 10 % of Geant4 results. In addition, TG‐43 parameters can be calculated. However, consideration should be given to the biological effectiveness of the spectrum at different depths. Spectral measurements show significant beam hardening with 1st HVL increasing from 0.55 to 1.20 mm Al after 11.50 mm of water filtration. This effect may be attributed to the significant loss of low energy characteristic photons. Furthermore, the degree of beam hardening is dependent of the material, with 1st HVLs of 1.20 and 1.03 mm Al after 11.50 mm of water and Lucite respectively. The biological effect is quantified by calculating the number of single and double strand breaks. The number of strand breaks for the 50 kVp x‐ray spectrum is similar to that of I‐125 radiation.
Sci‐Sat AM(2): Brachy‐09: Investigation of catheter displacement in HDR prostate brachytherapy
Authors: Hunt DC , Soliman H , Sankreacha R , Morton G
Published: July 2008

During prostate cancer treatment with HDR brachytherapy, catheters are inserted into the prostate. Between planning and treatment, catheters may move inferiorly due to edema. If undetected, treatment proceeds without correcting the catheter displacement, and an incorrect treatment is delivered. The purpose of this study was to investigate the consequences of catheter displacement on prostate coverage and critical structure avoidance. Ten patient plans were selected in which movement of the catheters had been observed. The original treatment plan, generated using Nucletron PLATO (ver. 14.3.2), was adjusted introducing inferior catheter offsets of 5, 10, 20, and 30 mm. The original treatment dwell times were re‐entered into the offset plans to determine the consequences of the displacement. DVH data was calculated for the prostate, rectum, urethra, and bladder. Prostate V100 decreased from 99% to 36% over the ten patients studied. For the urethra, the D10 increased (114.1% to 128.2%), as did the V125 (2.7% to 12.8%). In the rectum the V75 initially increased as the catheters shifted inferiorly, but dropped as the shift increased beyond 10 mm. In the penile bulb the V75 increased as a function of shift (from 2.1% to 44.8%). Every effort should be made to ensure that the catheters do not move during prostate treatment. A small shift, 5 mm, would result in a small deviation of the dose distribution. In this case a re‐optimization of the plan is unnecessary. Larger shifts will have a serious impact on the dose delivered to the prostate and to sensitive normal structures.
Platelet function testing: practice among UK National External Quality Assessment Scheme for Blood Coagulation participants, 2006
Authors: Jennings I , Woods T A L , Kitchen S , Walker I D
Published: July 2008

Aims:

Platelet function testing forms an important part of the laboratory investigation of a bleeding tendency; however, little standardisation and quality control is available for these tests. A UK National External Quality Assessment Scheme (UK NEQAS) for Blood Coagulation exercise sought to identify current practice among laboratories performing platelet function tests.

Methods:

A questionnaire was circulated in March 2006 to establish the current status of platelet function testing practice among participants of UK NEQAS. Participants were asked specifically about practice in bleeding time testing, PFA-100 analyser use, platelet aggregometry methodology and additional tests of platelet function.

Results:

169 returned questionnaires revealed that 26 centres used bleeding time, the PFA-100 analyser and platelet aggregometry in their investigations; 13 used bleeding time and the PFA-100 only; 33 used bleeding time and platelet aggregometry; and 23 used the PFA-100 with platelet aggregometry. 58 centres reported that they performed only bleeding times in their investigations, 10 reported use of the PFA-100 only, and 6 reported use of aggregometry only. Marked variability was observed in methodology for each of these tests, and in many cases no form of quality control was employed.

Conclusions:

The data confirmed the lack of standardisation in methodology employed in different centres. Updated guidelines and standardisation of platelet function assessment are required to facilitate comparability between centres.
Sarcoidosis of the nervous system
Authors: Joseph F G , Scolding N J
Published: July 2008

Although sarcoidosis is rarely confined to the nervous system, any neurological features that do occur frequently happen early in the course of the disease. The most common neurological presentation is with cranial neuropathies, but seizures, chronic meningitis and the effects of mass lesions are also frequent. The diagnostic process should first confirm nervous system involvement and then provide supportive evidence for the underlying disease; in the absence of any positive tissue biopsy, the most useful diagnostic tests are gadolinium enhanced MRI of the brain and CSF analysis, although both are non-specific. The mainstay of treatment is corticosteroids, but these often have to be combined with other immunosuppressants such as methotrexate, hydroxychloroquine or cyclophosphamide. There is increasing evidence that infliximab is a safe treatment with good steroid sparing capacity.
When the patient fails to respond to treatment: myasthenia gravis
Authors: Hilton-Jones D
Published: July 2008

Myasthenia gravis is one of the most satisfying neurological disorders to treat. There are few other conditions in which therapeutic intervention can take a patient from being bed-bound and ventilated to normality. Most patients present with less severe symptoms, but even mild extraocular muscle weakness can be profoundly disabling. The standard therapeutic approach is successful for most patients, which can make the non-specialist neurologist somewhat blasé about its management. However, panic can set in when the standard approach fails. Failure is often the result of incorrect diagnosis, or inappropriate use of first-line treatments. This article outlines the main reasons for failure and gives advice on alternative therapeutic strategies.
Community-acquired bacterial meningitis in adults
Authors: Schut Ewout S , de Gans Jan , van de Beek Diederik
Published: July 2008

Despite the availability of effective antibiotics, vaccination programmes and skilled acute-care facilities, there is still a significant mortality and morbidity from bacterial meningitis. Neurologists are often called on to “rule out bacterial meningitis”, which can be difficult with the history and physical examination alone. In this review the authors will discuss the epidemiology, diagnosis and treatment of acute community-acquired bacterial meningitis in adults, focussing particularly on the management of patients with neurological complications, and stressing the importance of adjunctive dexamethasone.