bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐C‐BRB‐09: Sensitivity of a Novel External X‐Ray Treatment for Age‐Related Macular Degeneration to Variations in the Position of the Eye
Authors: Taddei PJ , Chell E , Firpo M , Hansen S , Gertner M , Newhauser WD
Published: April 2010

Purpose: Age‐related macular degeneration (AMD) is the leading cause of blindness of the elderly in the United States. A novel external beam treatment has been developed for the treatment of AMD that delivers a 16‐Gy prescribed dose to the fovea (clinical target volume, CTV) using three overlapping low‐energy x‐ray fields while adequately sparing normal tissues in the eye and brain. The purpose of this study was to test the sensitivity of the successful delivery of the prescribed dose to the CTV and of the sparing of normal tissues to plausible variations in the position of the eye. Method and Materials: In the standard case, the axial length of the eye is 24 mm and the gaze is straight ahead. Using Monte Carlo simulations, we examined the overlap of the three beams on the posterior surface of concentric spheres with radii from 10 mm to 14 mm. In addition, we calculated absorbed dose in the CTV and structures at risk while varying varied the gaze angle by ±5° vertically and laterally and the displacement of the eye ±1 mm in all orthogonal directions. Results: The three fields did not diverge for all radii tested. For variations in the position of the eye, the dose to the CTV was stable (<6% fluctuation), the maximum dose to the sclera was <20 Gy, the maximum dose to the optic disc was <0.7 Gy, and the mean doses to the optic nerve, lens, and cornea were <0.3 Gy. Conclusion: The results of this study provide strong evidence that variations in the position of the eye will not hinder the successful delivery of the prescribed dose to the CTV and the sparing of critical structures for this stereotactic radiosurgical treatment of AMD. Conflict of Interest: Research sponsored in part by Oraya Therapeutics, Inc.
WE‐C‐BRC‐02: Combined Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE‐MRI) and Magnetic Resonance Thermal Imaging (MRTI) for Optimal Hyperthermia Treatment of Advanced Extremity Sarcomas: Fifteen Patients Update
Authors: Craciunescu O , MacFall J , Soher B , Stauffer P , Maccarini P , Jones E , Larrier N , Wong T , Carroll M , Dewhirst M , Vujaskovic Z
Published: April 2010

Purpose: To deliver optimal hyperthermia (HT) treatments for patients with advanced extremity sarcomas using DCE‐MRI and MRTI Method and Materials: Patients were treated on a protocol using radiotherapy consisting of 45 Gy and once a week HT for 5 weeks in a setting that allows the use of a 1.5 T GE magnet for imaging. Pre‐ and post first HT treatment DCE‐MR images were acquired and analyzed with software from iCAD Inc. (Nashua, NH) based on a full time point pharmacokinetics (PK) analysis that measures tumor's permeability (Ktrans) and extracellular volume fraction (Ve). Multi‐slice temperature rise images were obtained using the proton resonance frequency shift technique during heating in a 140 MHz phased array HT applicator and compared to invasive temperature measurements. Thermal dose metrics were calculated and correlated with response and with the PK parameters. Results: Fifteen patients were enrolled on this protocol; ten patients were heated. Permeability maps derived from DCE‐MR images were used to guide the placement of the invasive catheter to span regions varying from high to low perfusion. The MRTI images were used to steer the power, with the intent of heating the tumor uniformly while maintaining surrounding normal tissue at lower temperatures. From the evaluable HT treatments, we achieved excellent correlation (ΔT<1°C) between the MRTI and invasive measurements. As a trend, patients that were either pathological complete or partial responders had a decrease in Ktrans. The Ve parameter showed no clear trend with pathological response or % necrosis. As expected, tumors that were more vascularized (higher Ktrans) heated less than tumors with a high degree of necrosis or fluid pockets. Conclusion: DCE‐MRI coupled with MRTI provides information on tumor environment that can improve planning, delivery, and evaluation of HT treatments.

Supported by a grant from the NCI CA42745.
WE‐D‐304A‐04: Performance of a Method to Aid Breast Ultrasound Interpretation Using Image Processing and Case‐Based Reasoning
Authors: Andre M , Galperin M , Ojeda‐Fournier H , Olson L , Berry A , Comstock C , O'Boyle M
Published: April 2010

Purpose: To examine factors that may impact accuracy, reproducibility of Breast Ultrasound CADx software. Goal for CADx is standardized reporting of findings using well‐defined descriptors and to aid accuracy and reproducibility of interpretation by radiologists. Method and Materials: Breast Companion® (BC, Almen Laboratories and UCSD) provides tools to analyze breast masses. It computes 9 features of the mass, compares these to images in Reference Library of masses with known findings. Using Relative Similarity it retrieves instantaneously a cluster of the most similar cases and outputs numerical data including Computerized Lesion Assessment (CLA) following the ACR BI‐RADS assessment category (1 through 5). Results: On 596 cases with known findings BC achieved ROC Area 0.98±0.02, Sensitivity 99.7%, Specificity 96.1%, significantly higher than four experienced radiologists who read the same cases (ROC Areas 0.88 to 0.90±0.02). Increasing the number of cases in the Reference Library from 41–331 and the number Test Set cases from 20–924 keeping mix same, ROC varied from 0.90±0.07 to 0.98±0.02 (NS). In 55 cases (40% malignant) with confirmed findings BC calculated CLAs for radial and anti‐radial images that were highly correlated, not significantly different by two‐tailed t‐test (p>.5). CLA for simple cysts was 2.0, mean for complicated cysts was 2.5, 3.0 for solid benign and 4.5 for malignants. 28 subjects (40% malignant) were analyzed who had exams of the mass on two different occasions within 3 weeks on GE and Siemens (NS difference). Simulated masses of were imaged over 3 months at 9, 10, 13 MHz with varying gain, dynamic range, focal depth post‐processing. CLA was stable and independent of or linearly scaled to machine parameters. Conclusion: The BC system accuracy is high, stable over range of conditions. Measured parameters are dimensionless, relative to their backgrounds so it appears normalization achieves mitigation in machine effects.
WE‐D‐210A‐04: Novel PET Probes to Image the Immune System and Cancer — From Discovery to Clinical Applications
Authors: Radu C
Published: April 2010

Monitoring immune function using molecular imaging could significantly impact the diagnosis and treatment evaluation of immunological disorders and therapeutic immune responses. Positron Emission Tomography (PET) is a molecular imaging modality with applications in cancer and other diseases. PET studies of immune function have been limited by a lack of specialized probes. We identified [18F]FAC (1‐(2′‐deoxy‐2′‐[18F]fluoroarabinofuranosyl) cytosine) by differential screening as a new PET probe for the deoxyribonucleotide salvage pathway. [18F]FAC PET enabled visualization of lymphoid organs and was sensitive to localized immune activation in a mouse model of anti‐tumor immunity. [18F]FAC microPET also detected early changes in lymphoid mass in systemic autoimmunity and allowed evaluation of immunosuppressive therapy. We have also developed a series of [18F]FAC analogs with improved pharmacokinetic properties. Data in animal models and preliminary studies in humans support the use of [18F]FAC and its analogs for immune monitoring by PET and suggest a wide range of clinical applications in immune disorders and in certain types of cancer.

Research sponsored in part by Sofie Biosciences through a UC Discovery grant.
WE‐D‐213A‐02: Establishing a Stereotactic Body Radiation Therapy (SBRT) Clinical Program, Part 2: Clinical and Radiobiological Considerations
Authors: Read P , Kavanagh B
Published: April 2010

Stereotactic Body Radiation Therapy (SBRT) has emerged as an important form of cancer therapy with broad application across a spectrum of tumor types in the primary and metastatic settings. The capability of safely administering a very high dose of therapeutic radiation to discrete extracranial tumor sites has raised new questions about the radiobiology of high dose per fraction treatment. Accumulating clinical experiences are yielding new insights into practical aspects of tumor and normal tissue responses to high dose per fraction treatment.

The current practice of SBRT has evolved to some extent from knowledge gained from principles learned from the practice of cranial stereotactic radiosurgery (SRS). For the integration of SBRT into clinical practice, medical physicists and radiation oncologists are advised to collaborate closely to establish clear guidelines for normal tissue dose constraints and tumor dose prescription practices that are suitable to their own clinical environment. Published literature relevant to this objective will be discussed. A consistent strategy for contouring sensitive organs is encouraged. The technological challenges introduced by the high dose and high precision paradigm of SBRT are presented and the vital relationship between physicist and physician in this context cannot be overemphasized.

The radiobiological issues that have been parsed by this new paradigm of treatment will be explored, including understanding of conventional, hypofractionated and single dose treatments, radiobiological modeling, and the concepts of equivalent doses. Future trends in SBRT will be discussed. Clinical outcomes after SBRT in a variety of setting will be summarized.

Learning Objectives:

1. Review and understand the major issues related to the use SBRT for, including key strategies for uniform contouring and determination of organ tolerances.

2. Review and understand the common clinically observed normal tissue responses to SBRT and the inferences to be drawn regarding the practical radiobiology of high dose per fraction therapy

3. Discuss these new paradigms of fractionation as they relate to conventional regimes, including hypofractionation and single dose treatments and their radiobiological threshold effects.

4. Review potential future application of SBRT
WE‐E‐BRB‐04: Comparison of IMRT Verifications with a Two‐Dimensional Array of Diodes and a Commercial Portal Dosimetry System
Authors: Guerrero M , Patel I
Published: April 2010

Purpose: The purpose of this work is to replace our IMRT verification protocol with a commercial portal dosimetry system. Currently, our department performs IMRT verifications for prostate patient's plans using a commercial two‐dimensional array of diodes (MapCheck from Sun Nuclear). Our goal is to develop an equivalent QA program using a commercial electronic portal imager (EPID) to simplify and expedite the plans verifications as well as to increase the resolution of our measurements. Method and Materials: Using Varian aS500 portal imager with the Portal Dosimetry Calculation (PDC) from Eclipse (commissioned according to manufacturer's recommendations), we perform verifications for 15 prostate patients treated at our department. We use a beam‐by‐beam Γ analysis with a 3%3mm criteria for acceptance and compare the results with our standard verification method using a discrete two‐dimensional array of diodes. We compare the Γ scores for absolute dose and calculate beam‐by beam space correlations between the portal imager and MapCheck. Results: The clinical IMRT verifications performed with the EPID are consistent with the ones performed with our commercial two‐dimensional diode array. The Gamma scores show a correlation coefficient of 0.77 and almost all the beams within the acceptance limits in MapCheck are within acceptance limits for the EPID. The 3 beams outside the acceptance limit in MapCheck are also outside the acceptance limit in the EPID system. The spatial correlation, although not perfect, is acceptable. Conclusion: The EPID system with the Varian aS500 and the PDC calculation from Eclipse show essentially equivalent results for prostate IMRT verifications as the two‐dimensional diode array. The EPID system has the advantage of set‐up simplicity, shorter time and higher resolution and can be implemented as the primary IMRT verification method.
WE‐E‐BRB‐07: Quality Assurance of Proton Range Compensators by CT Scanning
Authors: Zheng Y , Klein E , Low D
Published: April 2010

Purpose: Patient specific range compensators (RCs) are required in passively scattered proton therapy. Conventionally, quality assurance (QA) of RC is performed by either a visual inspection or spot check of thicknesses for some drill points (e.g. 4). A more comprehensive QA of RCs is needed for precise delivery of proton beams. The purpose of this study was to develop a QA procedure by use of computed tomography (CT). Method and Materials: For the procedure, one or more range compensators would be scanned with a CT scanner. Software was developed to automatically segment the range compensator on CT images and calculate the thickness matrix for the RC. The CT‐scanned RC thickness matrix was then compared to the expected one, which was reconstructed from the DICOM ION Radiotherapy Plan exported from a proton treatment planning system. The actual milling tool size and shape were taken into account when the RC was reconstructed. The scanned RC thickness matrix was automatically aligned to the planned RC matrix. In addition to comparing the physical thickness of the RC, we also verified the water equivalence thickness of the range compensator based on the CT scan. This would allow us to detect possible impurities or other defects of the RC. As part of the validation, we tested not only an unaltered RC, but RC that was damaged or altered post‐construction. Results: We developed software to process the scanned CT images of the RC and reconstruct the planned RC from the radiation therapy treatment plan. We compared both the physical thickness and water equivalent thickness between the scanned RC and planned RC to quality assurance the manufacturing of the RC. Our process was able to detect deviations of less than 2 mm. Conclusion: We have developed a procedure to efficiently and comprehensively QA the RC.
WE‐E‐304A‐02: Development of Low Dose X‐Ray Phase Contrast CT Using a Novel Projection Retrieval Reconstruction Algorithm
Authors: Fahimian B , Cloetens P , Mao Y , Lee E , DeMarco J , McNitt‐Gray M , Miao J
Published: April 2010

Purpose: In contrast to attenuation based x‐ray imaging, phase contrast x‐ray imaging, produces radically enhanced images of soft tissues through imaging of the phase shift cross‐section, which is 100–1000 larger than the corresponding x‐ray attenuation cross‐section. One obstacle in the development of phase contrast x‐ray CT (PCXCT) for medical imaging is the radiation dose imparted to the patient due to large number of projections and flux required for an adequate image quality. Here we develop and quantify a methodology for low dose PCXCT using novel iterative Fourier based projection retrieval reconstruction algorithm that aims to solve the reconstruction problem from a limited number of projections through the use physical and mathematical constraints as well as the oversampling method. Materials and Methods: An image quality phantom, containing multiple contrast visibility and resolution inserts, was imaged at the European Synchrotron Radiation Facility (ESRF). Conventional reconstructions were produced via Filtered Back Projection (FBP) using the full set of 200 projections. Reconstructions using the projection retrieval algorithm were made with 50–60% fewer projections. The image quality of the reconstructions were quantitatively compared using SNR, CNR, and resolution. Results: With 60% fewer projections, the methodology matched the resolution of the FBP reconstruction, exceeded the SNR of the FBP by factor of 1.8, and exceeded the CNR of the FBP by factor of 1.7. No geometric deformations were observed due to the undersampling of the number of projections. Conclusions: The results indicate that the developed algorithm can reproduce reconstructions of same or superior quality using 50–60% fewer projections and hence radiation dose than FBP. Conflict of Interest: A portion of this research was sponsored by TomoSoft Technologies, LLC.
WE‐E‐304A‐07: Clinically Relevant FROC Analysis
Authors: Chakraborty DP
Published: April 2010

Purpose: While it has been established that the free‐response receiver operating characteristic (FROC) method generally yields more statistical power than the receiver operating characteristic (ROC) method in localization tasks, it is not clear if the higher power is clinically‐relevant. Clinically‐relevant power is defined as the sensitivity of an analysis method to a modality induced change in the detectability (e.g., contrast) of clinically‐relevant lesions. The purpose of this work was to develop a new clinically‐relevant figure or merit and compare the powers of ROC, traditional FROC and the new FROC method. Method and Materials: In traditional lesion‐based FROC the y‐axis is normalized to the total number of lesions and the different clinical‐relevance of lesions is not taken into account. In case‐based analysis the y‐axis is normalized to the total number of abnormal cases and the method accounts for different clinical‐relevance of lesions. A case‐based figure of merit was developed that weights the lesions according to their clinical importance, and the search‐model simulator was used to compare the statistical powers of ROC and lesion‐based and case‐based FROC for case sets with two lesions per abnormal case, one with zero weight (e.g., a benign lesion) and the other with unit weight (e.g., a high‐morbidity lesion). The modality effect was modeled by changing the contrast and probability of the lesion being found during search. Results: Unless the modality effect decreased the contrast of the unit‐weight lesions, the power for case‐based analysis was comparable to lesion‐based FROC. Either FROC method exceeded the power of ROC. Conclusion: Case‐based analysis is expected to better correlate with clinical outcome. It does not sacrifice the statistical power of traditional FROC.
WE‐E‐213A‐04: Practical Aspects of Electron Beam Dosimetry
Authors: Gerbi B
Published: April 2010

Electron beam dosimetry can be a deceptively simple endeavor. On one hand, the process of measuring and using unrestricted electron cone factors is remarkably straight forward. However, making measurements in restricted fields especially at extended treatment distances can prove to be quite a challenge, especially if the field is extremely narrow. Ionization chamber correction coefficients for cylindrical and plane‐parallel chambers can depend on many factors and ensuring that the correct factors are applied for measurements at depth in water or solid phantoms can be confusing.

This talk will cover proper measurement set up and technique, problems and pitfalls associated with detector selection for various electron measurement situations, chamber response characteristics that should be known and determined before use for electron dosimetry, and efficient techniques for performing routine commissioning measurements and special dosimetry for electron beams. The influence of TG‐51 calibration protocol on routine clinical measurements will also be covered along with some clinical techniques where electron beam measurements are particularly challenging and interesting.

Learning Objectives:

1. Ionization chamber response characteristics in electron beams

2. Selection of detectors for measurements in electron beams

3. Use of ionization chambers and other detectors in electron beams measurements

4. Special measurement situations: restricted field measurements, measurements at extended distances, measurements in non‐water phantoms

5. Clinical situations involving special electron beam measurements
TH‐SAM‐304A‐01: FFDM in the Field: Physicist's Role in the QC of Third‐Party Review Work Stations
Authors: Keener C
Published: April 2010

The FDA requires that new mammography modalities follow a QC program which is similar to the MQSA final rules for film‐screen mammography. Early full‐field digital mammography (FFDM) manufacturers fulfilled this requirement by publishing QC manuals which covered all the required medical physicist and technologist QC tests for their FFDM unit and soft‐copy review work station.

In recent years, the FDA has allowed FFDM users to interpret digital mammograms on monitors other than the those provided by the FFDM manufacturer. There are several 5MP monitor manufacturers each with their own mammography QC requirements, documentation, software, and photometers. These monitors may also be rebranded and installed by PACS vendors with their own QC manuals. A physicist surveying a FFDM unit may find many combinations of FFDM manufacturer, monitor manufacture and PACS vendor QC requirements for the review workstation. Further complicating this, a single FFDM unit may use multiple, work stations from different manufacturers or a single work station may be used by multiple FFDM units perhaps from different manufacturers. A consulting medical physicist visiting multiple sites is especially likely to find a changing variety of combinations. Because these are all covered under MQSA regulations, it is important the physicist perform and document the correct QC tests.

This lecture will review the various monitor QC tests suggested or required by TG‐18, the major FFDM manufacturers, current 5MP monitor manufacturers, and PACS vendors. Suggestions will be offered on sets of tests which can be performed on a large number of monitors regardless of their manufacturers. Suggestions will also be made on surveys which will fulfill the requirements of nearly all manufacturers. Such a surveys may include may tests which are not required for the monitor tested but are simple to perform.

Learning Objectives:

1. Understand the review workstation tests required by FFDM manufacturers and the requirements those manufacturers have for third‐party monitors.

2. Understand the TQ18 monitor tests which are applicable to current 5MP monitors.

3. Learn the QC tests required by various 5MP monitor manufacturers and PACS vendors.
TH‐SAM‐304A‐02: Digital Detector QC, Tips and Problems
Authors: Berns E
Published: April 2010

Digital mammography has become the technology of choice for breast imaging with several FDA‐approved systems already available and more on the way. Digital detectors in mammography have different characteristics compared to the traditional screen‐film systems and require different quality control tests by the FDA approval process. This lecture is going to discuss the practical issues for the medical physicist who wants to learn the differences in these Quality Control tests and how they impact the mammography facility and ACR accreditation. The lecture will be broken into several parts. The first will review currently available FFDM equipment and their respective Quality Control tests. The second part will compare similar QC tests and discuss the key differences. The third part will look ahead to the new FFDM QC program being developed by the ACR.

Learning Objectives:

1. To describe current quality control procedures for FFDM systems.

2. To review the impact of QC on ACR accreditation for FFDM systems.

3. To preview the forthcoming ACR FFDM QC program.
TH‐A‐303A‐01: Practical Procedures for Achieving and Maintaining ACR CT Accreditation
Authors: Pickens D
Published: April 2010

Accreditation of computed tomography systems is increasingly important as reimbursements become tied to the successful achievement and maintenance of accreditation status. This presentation reviews the technical requirements for the medical physicist who will be in charge of performing quality assurance and ACR accreditation testing of a CT scanner. These duties include establishing schedules for routine quality assurance testing, performing pre‐submission and annual testing, and performing testing for the ACR submission. All of these are reviewed from a practical standpoint of performing the required studies in an efficient manner with appropriate record keeping and documentation.

Learning Objectives: Attendees will gain understanding of the

1. Requirements for the physics testing for ACR accreditation

2. Practical aspects of testing CT systems

3. Performance of annual surveillance testing and pre‐application testing

4. Establishment of routine quality assurance protocols and record keeping
TH‐B‐211A‐02: Clinical Implementation of Respiration Motion Correlated Imaging, Treatment Planning and Delivery
Authors: Vedam S
Published: April 2010

Respiratory motion is a significant factor in determining a suitable planning target volume (PTV) that surrounds the demonstrable gross tumor volume (GTV) in the radiotherapy of mobile lesions. Historically, a “one‐size‐fits‐all” margin derived from population statistics has been employed to account for such motion. The advent of respiratory phase correlation (4D) and multi‐slice CT technology has enabled patient‐specific determination of both demonstrable tumor volume and its motion from a single imaging study. Management of such additional information during treatment planning and delivery however presents several challenges. Furthermore, guidelines for establishing clinical treatment planning and delivery protocols based on respiratory correlated imaging data differ from one institution to the other. The purpose of this presentation is to educate the community on the different respiratory correlated radiotherapy approaches currently available and compare the benefits and pitfalls in each case. Special focus will be on treatment planning, dose calculation and treatment delivery related issues.

After the course, the attendees should be able to:

1. Understand the different respiratory correlated treatment planning and delivery approaches

2. Compare the benefits and pitfalls of each of the above approaches

3. Develop and establish respiratory correlated imaging, treatment planning and

4. delivery appropriate to the available equipment
TH‐C‐BRD‐05: Amplitude Gated Deep‐Inspiration‐Breath‐Hold Treatment for Heart Dose Reduction in Left Breast Cancer Patients: Residual Motion and Breath‐Hold Threshold
Authors: Veale C , Wang Z
Published: April 2010

Purpose: Amplitude gated deep‐inspiration‐breath‐hold (DIBH) treatment technique may greatly reduce cardiac dose for left‐breast cancer patients compared to irradiation under free‐breathing. This study investigates the correlation between inter/intrafractional motion and the amplitude gated breath‐hold threshold. The outcome of this study can be used to guide setting the thresholds and margin determination for patients to be treated with this technique. Method and Materials: 12 left‐sided breast cancer patients were studied in this investigation. EPID device was used for cine image acquisition. Real‐time position management® (RPM) was used in accordance with amplitude gated DIBH technique for motion management. Megavoltage cine images taken during the treatments were used to determine chestwall motions. Image analysis of the DICOM cine images were performed using MATLAB® and Image J®. Threshold sizes were compared with maximum intrafractional chestwall motions in 282 sessions, separated into superior, middle, and inferior regions. Interfraction motion was measured by picking cine images acquired during different sessions at the top and bottom of the threshold for each patient. Results: Breath‐hold level was found to have large variations among various patients. The mean intrafractional motion as measured with cine EPID images was 0.68 mm, with a standard deviation of 0.54 mm. For each given mm increase in intrafraction chestwall motion, the threshold increased an average of 0.38, 0.39, and 0.14 mm for superior, middle, and inferior regions, respectively, for the 12 patients. Interfraction chestwall motion increased with increasing threshold size. Mean interfractional motion was 3.34 mm, with a standard deviation of 2.31 mm. A 1 mm increase in threshold size led to an average 0.88 mm increase in mean interfraction motion. Conclusions: A correlation exists between the breath‐hold level and intrafractional chestwall motion. Threshold correlations with intra/interfraction motion were also found. Increasing the threshold leads to both increased inter and intrafractional motion.
TH‐C‐BRD‐07: Small Field Intracranial Radiosurgery Using Intermediate Energy X‐Rays (1 MV) to Improve Dose Gradient and Homogeneity
Authors: Keller BM , Pignol JP , Beachey DJ
Published: April 2010

Purpose: The radiological penumbra of small radiosurgical dose fields is dictated by the range of secondary electrons, which in turn is determined by the primary photon energy. The purpose of this work is to experimentally compare the dose gradient and homogeneity of a multiple beam dose distribution in a radiosurgery head phantom for 6 MV versus 1 MV while minimizing geometrical penumbra. Methods and Materials: A commercial radiosurgery head phantom (LUCY™) containing Gafchromic EBT film was used for all irradiations. A digital microscopy imaging system resolved steep dose gradients in the films and a Siemens linac was modified to produce 1 MV x‐rays. The XKnife™ RT3 TPS was modeled for both 1 and 6 MV to compare with measurements. Two‐beam (90° apart) and eighteen‐beam (10° apart) irradiations were done in the same plane as the film using a 5 mm tertiary collimator. The geometrical penumbra ranged from 0.2–0.4 mm, equivalent to a linac with a 1 mm focal spot with collimator 20 cm from the isocenter. Dose was normalized at the isocenter at depth 7 cm in phantom. Results: For the two‐beam irradiations, the 90%–50% and 90%–10% dose gradients at the beam intersection were 1.7 & 4.7 mm (6MV) versus 0.5 & 1.3 mm (1 MV) for identical irradiation conditions. For the eighteen‐beam arc, the 90%–80% & 90%–60% dose gradients in the plane of irradiation were 0.84 & 1.7 mm (6MV) versus 0.29 & 0.9 (1 MV). In all cases, the homogeneity across the isocenter was superior for 1 MV. The dose at the entrance of each beam was greater for 1 MV. Conclusions: A 1 MV x‐ray beam showed superior dose gradient and homogeneity compared to 6MV for the irradiations examined at the expense of an increase in dose at the beam entrance for the lower energy.
TH‐C‐BRC‐08: Integration of Cone Beam CT Imaging and a Small Animal Conformal RT Device Using a 6DOF Robotic Arm
Authors: Sharma S , Chao M , Moros E , Corry P
Published: April 2010

Purpose: To integrate cone beam computed tomography (CBCT) imaging technology into a small animal conformal radiation therapy device (SACRTD) using a six degrees of freedom (6DOF) high accuracy/precision robotic arm. Method and Materials: A 225kV dual focus (0.4mm and 3mm) X‐ray tube (GE Seifert Isovolt Titan) is used for both radiation and imaging. An industrial robot (Adept Viper S650) is used for positioning and motion of a small animal for targeted radiation delivery and CBCT imaging with positional repeatability of ±0.020 mm in XYZ direction and angular precision of ±0.2°. A series of 2D‐radiographic projection images were recorded in cone beam mode with a flat panel amorphous silicon detector (Perking Elmer), which captures 1024 by 1024 pixels images (200μm pixel size) at a frame rate of 7.5Hz. An open source CBCT reconstruction tool (OSCAR‐2, University of Toronto) using Feldkamp‐Davis‐Kress (FDK) filtered back projection algorithm was employed for CBCT image reconstruction. Results: Initial testing of the CBCT system using phantoms and mice was successful. Radiographs were cropped and downsampled to a spatial resolution of 0.4mm. Reconstructed matrices had dimensions of 181×267×97 voxels with 0.3mm×0.3mm×0.3mm voxel spacing. With the current computer the entire acquisition and reconstruction procedure takes > 7 minutes. The OSCAR‐2 algorithm offers various reconstruction filters, but more sophisticated tools specific for small animal imaging are needed to improve the quality of CBCT images. Conclusion: This work demonstrated that a 6DOF robot is an excellent device for moving/rotating a small laboratory animal for acquiring high spatial resolution radiographs with the necessary accuracy and precision for successful CBCT reconstruction. It also demonstrated that an open source CBCT software tool could be adapted to work with the SACRTD. The integration of CBCT imaging into the SACRTD opens new research paths requiring image guided radiation delivery to specific structures/volumes in small animals.
TH‐C‐303A‐01: Initial Clinical Experience with Electromagnetic Localization and Tracking for External Beam Partial Breast Irradiation
Authors: Afghan MKN , Eulau S , Morris A , Hallam P , Ye J , Wong T , Cao D , Zeller T , Mate T , Shepard D
Published: April 2010

Purpose: The Calypso® 4D Localization System™ (Calypso Medical) uses non‐ionizing AC electromagnetic radiation to localize and track small wireless devices (called Beacon® transponders) implanted in or near a patient's tumor. We report on the first clinical experience with the use of the system for localizing and tracking the lumpectomy cavity during external‐beam accelerated partial breast irradiation (EB APBI). Method and Materials: The study included patients treated receiving EB APBI on an IRB approved protocol. Thirteen patients were implanted with both gold markers (GM) and beacon® transponders and two patients were implanted with beacon® tranponders alone. For patients in whom MRI follow‐up was anticipated, two removable interstitial breast catheters were inserted and afterloaded with gold markers and transponders. The catheters were removed post radiation therapy. Initial alignment was performed using lasers. For patients with gold markers, orthogonal images were used to obtain the necessary shift. The shift values were compared to the shift predicted under electromagnetic guidance. During treatment, Calypso was used to track the target motion. Results: Fifteen patients have been studied, and 93 treatment fractions were analyzed. The catheters and transponders overall showed good stability with inter‐transponder distance changes of less than 2 mm. Calypso based setup can be performed in less than 2 minutes. An average residual setup error of 10.29 mm was determined using gold markers. For the 63 fractions analyzed, the difference between the residual setup error determined by the GM and the Calypso system on average was 1.5 mm. Tracking showed regular motion in the range of 2–3 mm with occasional deeper breaths exceeding 4–5 mm. Conclusion: Results show excellent agreement between gold markers and electromagnetic guidance in EB APBI with electromagnetic guidance providing a more rapid setup and real time tracking during delivery. Research sponsored by Calypso Medical.
TH‐C‐303A‐04: Evaluation of 3D Surface Camera System in Patient Setup for HN RT
Authors: Gopan O , Wu Q
Published: April 2010

Purpose: To evaluate the usefulness of a 3D surface camera system (AlignRT) in detecting rigid and non‐rigid setup errors during head and neck radiotherapy. Methods and Materials: To evaluate the accuracy of AlignRT's surface registration algorithm, both translational and rotational movements of a known magnitude were manually applied in Pinnacle to transform a helical CT scan. The skin contours of both the primary helical CT scan and the transformed helical CT scan were transferred to AlignRT, where the transformed surface was registered to the primary surface. The changes that were reported by the AlignRT system were compared to the manually applied motions from Pinnacle. To evaluate the usefulness of AlignRT for rigid and non‐rigid patient setup, a retrospective analysis was performed on the helical CT scans of eleven patients. The registrations in Pinnacle based on bony (either skull (rigid) or vertebrae (non‐rigid)) anatomy were compared to the surface (either head (rigid) or shoulder (non‐rigid)) registrations in AlignRT. Results: The accuracy of AlignRT's surface registration algorithm was, on average, 0.041 ± 0.036 degrees and 0.075 ± 0.100 mm. The accuracy of the optical system was, on average, 0.087 ± 0.912 degrees and −0.153 ± 1.996 mm. For shoulder (non‐rigid) guidance, if we use 2*standard deviation for 95% confidence level, the accuracy of the optical system was within 3 degrees for rotations in the vertical and longitudinal directions, but 5 degrees for the lateral direction. For translations, the accuracy was more than 10 mm.

Conclusion: While the feasibility of using the AlignRT system for head (rigid) guidance in the setup of HN patients was demonstrated, the use of the system in non‐rigid patient setup yielded undesirable results.
TH‐C‐304A‐07: Real‐Time Tracking of the Pulmonary Veins in 3D Ultrasound of the Beating Heart
Authors: Bruder R , Ernst F , Schlaefer A , Schweikard A
Published: April 2010

Purpose: Currently effort is taken to use radiation therapy to cure heart diseases like arrhythmia. This approach requires high accuracy localisation and tracking of the pulmonary veins. Because of the high speed of motion of the heart, fluoroscopic tracking of fiducials or anatomical structures as in IGRT would on the one hand require high frame rates and, on the other hand, it would be dangerous to place fiducials near the target. We propose to use live 3D ultrasound to perform the landmark localization and tracking. Methods and materials: We have modified a GE Vivid7 dimension 3D cardiovascular ultrasound station for real‐time volume processing and target localisation. It is capable of providing ultrasound volume scans of the target region with more than 20 fps. A framework was established to upload and run image‐processing algorithms directly on the ultrasound machine which is necessary to handle the high amount of data. This prevents the bottleneck of Ethernet data streaming and external processing. We propose to localise the pulmonary veins using a template matching algorithm with multiple templates. Approximately 20 templates are manually generated during one heart beat cycle. To increase the speed and accuracy of the matching process, electrical pulse signals were recorded by the ultrasound station. This allows selecting two or three pulse‐dependent templates in the live matching stage. Results: The accuracy of the localization process is highly dependent on the templates chosen. The best results were achieved providing a full heart cycle as template data. As a compromise between speed and accuracy, we used 9×9×9 points as template, corresponding to 4.5×4.5×4.5mm3. Conclusion: The presented approach is a new and robust approach to semi‐automatically track small substructures in the beating heart. Furthermore, the generated signal is suitable as input to numerous prediction algorithms currently used to compensate for breathing motion in radiosurgery.
TH‐C‐304A‐08: Free‐Form Deformation Algorithm: Validation and Dosimetric Corrections for Breathing Motion Using 4D‐CT
Authors: Alasti H , Chow J , Markel D
Published: April 2010

Purpose: A Free‐Form Deformable (FFD) image registration algorithm in conjunction with 4D‐CT images was developed for dosimetric calculations, to incorporate internal organ motion and deformation. The motivation behind this work comes from the effects of tumor motion in the lung, which are significant under the free breathing radiotherapy. Methods and Materials: The FFD algorithm was developed using the cubic‐B‐spline method with smoothness corrections and registration point assistance to mark landmarks of interest. A graphical user interface (4DFFD) was created using GUIDE in MATLAB™ to encapsulate the deformation algorithm for voxel‐tracking. Validation of the algorithm was performed using the QUASAR Respiratory Motion Phantom with amplitude of 4 cm in the superior‐inferior direction, and a period of 4 seconds mimicking the lung tumour motion under free breathing. The 4DFFD has been applied to treatment planning of a lung cancer patient and dosimetry was calculated for a 6‐beam IMRT plan. Results: The phantom was imaged at 10 phases of motion using a GE light speed plus CT simulator, capable of 4D‐CT imaging. Using the 4DFFD software, nine phases of motion were registered to the mid phase and evaluated. In phantom the average geometric differences for each phase were in the range of 1.7 – 4.3 mm with average error of 3.2 mm, comparable to other image deformation algorithms such as Finite Element. Comparing the DVH for PTV, between the standard practice for lung at Princess Margaret Hospital versus our in‐house developed 4DFFD shows a peak difference of 10 cm3 at 4400 cGy, and a reduction of the dose coverage of the PTV. Conclusions: our developed 4DFFD can produce a realistic dose‐volume relationship under the free breathing motion in radiotherapy of lung cancer patients.
TH‐D‐211A‐02: Current Reimbursement Issues in Medical Physics 2009
Authors: Hevezi J
Published: April 2010

In the last year or two, new procedures in radiation oncology have become more common and issues surrounding their reimbursement have surfaced at the same time. The procedures of Stereotactic RadioSurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT) have now been recognized by most carriers as bonafide procedures to treat some cancers for their beneficiaries. With IMRT, these new procedures make liberal use of Image Guided Radiation Therapy (IGRT) to insure that the target tumors at the focus of these procedures are being treated precisely and accurately.

Because these new procedures involve planning and delivering large doses in a few fractions (hypofractionation), it is imperative that the radiation oncologist and medical physicist are “present” at each treatment fraction. The increase in complexity and treatment times for these procedures further insist on these presence requirements. Frequent imaging before and during treatment delivery require feedback from the radiation oncologist and medical physicist for accurate localization of the targets. Patients have the potential of injury if they are not supervised in the treatment delivery and there is greater onus on the treating Radiation Therapist to understand all of the mechanisms involved in these more complex delivery schemes. Unlike the presence requirements for HDR procedures which are rooted in a regulatory requirement (NRC and State agencies), the presence requirements for SRS/SBRT are rooted in the reimbursement values for these procedures with professional and technical times for the radiation oncologist and medical physicist.

Another area that has surfaced recently for activities of the medical physicist is in the fusion of image data sets to the base CT planning images used for treatment planning — not only for SRS/SBRT, but for IMRT and Conventional 3D where these image sets are utilized. Magnetic Resonance Imaging (MRI) is the most common image set one thinks of in fusing to the CT planning data set and has been used historically in cranial target RT. Other “foreign” image sets are coming to the fore also. These are PET and PET/CT data sets as well as Ultrasound and even, arteriograms. If these are DICOM compatible, most can be fused with the primary CT data set if the planning software is set up to accept these image sets. CPT 77370, Special Physics Consult is the primary CPT code used to cover this work, as the medical physicist (or dosimetrist under the supervision of the medical physicist) is primarily responsible for evaluating the goodness of anatomic fusion of these image sets to the primary CT data set. As with any work performed under CPT 77370, the request for fusion must come from the radiation oncologist in a signed/dated requisition and the medical physicist will generate a report back to the radiation oncologist referring to the congruence between the two image sets for a particular patient study. The report is signed/dated by the medical physicist, again, as with any
Revision, extension, and evaluation of a binaural speech intelligibility model
Authors: Beutelmann Rainer , Brand Thomas , Kollmeier Birger
Published: April 2010

This study presents revision, extension, and evaluation of a binaural speech intelligibility model (Beutelmann, R., and Brand, T. (2006). J. Acoust. Soc. Am. 120, 331–342) that yields accurate predictions of speech reception thresholds (SRTs) in the presence of a stationary noise source at arbitrary azimuths and in different rooms. The modified model is based on an analytical expression of binaural unmasking for arbitrary input signals and is computationally more efficient, while maintaining the prediction quality of the original model. An extension for nonstationary interferers was realized by applying the model to short time frames of the input signals and averaging over the predicted SRT results. Binaural SRTs from 8 normal-hearing and 12 hearing-impaired subjects, incorporating all combinations of four rooms, three source setups, and three noise types were measured and compared to the model’s predictions. Depending on the noise type, the parametric correlation coefficients between observed and predicted SRTs were 0.80–0.93 for normal-hearing subjects and 0.59–0.80 for hearing-impaired subjects. The mean absolute prediction error was 3 dB for the mean normal-hearing data and 4 dB for the individual hearing-impaired data. 70% of the variance of the SRTs of hearing-impaired subjects could be explained by the model, which is based only on the audiogram.
Excitation-based and informational masking of a tonal signal in a four-tone masker
Authors: Leibold Lori J. , Hitchens Jack J. , Buss Emily , Neff Donna L.
Published: April 2010

This study examined contributions of peripheral excitation and informational masking to the variability in masking effectiveness observed across samples of multi-tonal maskers. Detection thresholds were measured for a 1000-Hz signal presented simultaneously with each of 25, four-tone masker samples. Using a two-interval, forced-choice adaptive task, thresholds were measured with each sample fixed throughout trial blocks for ten listeners. Average thresholds differed by as much as 26 dB across samples. An excitation-based model of partial loudness [Moore, B. C. J. et al. (1997). J. Audio Eng. Soc. 45, 224–237] was used to predict thresholds. These predictions accounted for a significant portion of variance in the data of several listeners, but no relation between the model and data was observed for many listeners. Moreover, substantial individual differences, on the order of 41 dB, were observed for some maskers. The largest individual differences were found for maskers predicted to produce minimal excitation-based masking. In subsequent conditions, one of five maskers was randomly presented in each interval. The difference in performance for samples with low versus high predicted thresholds was reduced in random compared to fixed conditions. These findings are consistent with a trading relation whereby informational masking is largest for conditions in which excitation-based masking is smallest.