bluuebunny/crossref_metadata_2025 huggingface dataset:
TH‐A‐224A‐01: QA for Imaging Systems Used for Planning (CT, PET, MR)
Authors: Mutic S
Published: July 2006

Imaging for radiation therapy treatment planning has different goals than diagnostic imaging. Quality assurance (QA) of imaging devices (CT, PET, MR) which are used for radiation therapy imaging will therefore have different or additional goals compared to QA for diagnostic imaging purposes. Use of PET and MR imaging in radiation therapy is constantly increasing and reliable performance of these imaging modalities is important to avoid potentially significant errors.

Quality assurance for CT scanners used for radiation therapy scanning is relatively well established and defined. This process remains to be adequately defined for PET and MR scanners that are used for treatment planning. Evaluation of image quality of CT, PET, and MR scanners is generally adequately addressed by procedures which were established for diagnostic imaging. Design of QA protocols for radiation therapy scanning should be founded on procedures which are used for diagnostic imaging. Evaluation of mechanical accuracy and image spatial integrity is unfortunately not a major concern in diagnostic imaging and these parameters are often not sufficiently addressed in diagnostic QA protocols. All three imaging modalities have multiple potential sources of spatial and geometric errors and understanding of these parameters is necessary for design of an effective quality assurance program. The design of QA programs for these devices will be affected by the location of individual scanner and distribution of its utilization for diagnostic and radiation therapy imaging. Scanners which have dual purpose (diagnostic and treatment planning imaging) should have a QA program designed jointly by diagnostic and radiation therapy physicists to ensure that the program meets the needs of both groups.

The quality assurance for these imaging modalities in the radiation therapy goes beyond the QA of the scanners and should include evaluation of implementation of images in the treatment planning process. This should include evaluation of data transfer, image registration, potential degradation in image quality, image distortions, and evaluation of process for delineation of tumor and normal structure volumes. MR and PET images can contain biologically active regions which may not correlate with any readily visible anatomic features. Correct identification and use of these regions in the treatment planning process should be a major concern of the QA program.

This lecture will provide an outline and description of QA program for CT, PET, and MR scanners used in radiation therapy. The fundamental goals of such program will be described and information which can be used for establishment institution specific QA programs will be provided.

Educational Objectives:

1. Describe goals of QA programs for CT, PET, and MR scanners used for radiation therapy imaging.

2. Describe QA process for individual imaging devices.

3. Describe a concerns for verification of correct implementation of these imaging modalities in the treatment planning process.
TH‐A‐224C‐01: Long Term Clinical Experience Using Ultrasound Alignment
Authors: McNeeley S
Published: July 2006

The use of ultrasound localization in radiotherapy has been in wide clinical use since the late 90's. It is the one of the first imaged guided radiotherapy (IGRT) systems to be widely used. The most common site of localization has been the prostate using a transabdominal approach. The technique makes use of treatment planning contour volumes with their associated isocenter overlaid on spatially localized ultrasound images. The ultrasound images are localized to the linac isocenter using various methods that include: a robotic arm, inferred stereotactic cameras, or various optical tracking methods. The difference in position between the overlaid contours and the observed ultrasound structures provides the three dimensional patient correction.

Ultrasound localization has shown to be an efficient method of alignment but it does have limitations. Ultrasound images are often difficult to interpret. For prostate, the transabdominal approach takes advantage of the increased resolution when imaging through the bladder, typically positioned anterior and superior to the prostate. When patient's bladders are empty, degradation in prostate imaging typically occurs. Often, large patients necessitate using lower frequency ultrasound, which also degrades the image quality. Large patients may also limit the ability to perform a transabdominal ultrasound with the presence of a pannis. Additionally, the operator's capacity to capture and interoperate ultrasound images can vary, limiting the quality of the alignment.

This lecture will touch on some of the techniques used to improve ultrasound alignment quality. These techniques were developed at an institution where over 100,000 ultrasound alignments have been performed since 1998. Also, the results from several clinical studies will be presented. These include abdominal pressure effects, procedural changes improving alignment quality, comparison with daily CT, and complication rates of a hypo‐fractionated prostate protocol using ultrasound alignment.

Educational Objectives:

1. Techniques in improving ultrasound image quality during alignment.

2. Understanding the limitations in performing ultrasound alignment.

3. Procedural changes that can improve alignment quality.
TH‐B‐330D‐01: Quality Assurance Procedures for Digital Radiography
Authors: Peck D
Published: July 2006

The use of digital radiography is becoming the normal form of image capture replacing film. With film there are numerous Quality Assurance (QA) procedures that have been developed that cover the film processor, retake analysis, patient dose and overall system image quality. The QA procedures for digital systems are just now being developed. Since the digital detector technologies vary and with variations in image processing methods it may seem difficult to develop standardized QA procedures. Yet the endpoints of optimized image quality and minimized patient dose need to be obtained. Therefore the Physicist needs to use the knowledge of the detector characteristics and processing methods as tools to maintain QA on digital systems. These procedures need to be rigorous enough to provide QA, yet they must be flexible enough to work for different detectors, processing methods and system applications. This lecture will provide an overview of the testing procedures for digital radiographic systems and suggest procedures that can be used to provide QA in digital radiography.

Educational Objectives

1. Review detector testing procedures used to assess digital systems.

2. Review QA procedures used in radiography and relate these to digital technologies.

3. Suggest QA procedures that can be used to evaluate digital systems.
TH‐B‐ValB‐01: Optimizing MR Imaging Procedures: The Physicist as a Consultant
Authors: Lemen L
Published: July 2006

Every MR system has its strengths and weaknesses, often varying tremendously both within and between the various system designs. Added to that, each site will have its own priorities and styles of use of their system. For an MR physicist to best assist in optimizing imaging procedures, it is extremely important for that individual to be both well‐versed in basic MR physics, and to be able to recognize (and understand) the impacts and trade‐offs of the technology in a large variety of imaging situations. The physicist should be able to determine and evaluate problems in patient images as well as phantom tests.

For this presentation, the basic relationships between MR imaging parameters will be reviewed with an emphasis on their implementation in common clinical protocols. Examples of how they are adapted for specialized procedures will then be given to demonstrate trade‐offs between contrast requirements; imaging speed; spatial resolution; geometrical accuracy, and patient safety issues. How specific field strength and gradient configurations affect these options will also be examined. Differences in RF coil properties will be discussed from the perspective of optimizing applications for a facility.

Educational Objectives:

1. Understand the primary tissue contrast characteristics of the standard clinical sequences; methods of selective elimination of tissue signals; and the role of exogenous agents to alter contrast.

2. Know how to consider the interactions between SNR, spatial resolution and imaging speed and how their combined effects determine image quality for a variety of clinical situations.

3. Understand circumstances under which patient physiology and system configuration may require modification of image acquisition parameters to achieve optimal image quality.
TH‐C‐330D‐02: The Forum On Medical Physics Education: Outcomes and Directions for the Future
Authors: Hendee W , Mower H
Published: July 2006

Medical physics education leaves much to be desired. The depth and breadth of education of radiologists in the fundamental physics of their profession is simply inadequate when contrasted with the complexity of imaging technologies and the sophistication of imaging procedures. The use of image guidance and complex treatment delivery systems and algorithms in radiation oncology calls for a substantial increase in the level of understanding of physics and its applications by radiation oncologists. These needs provide excellent opportunities for medical physicists to improve their contributions to the education of their physician colleagues, and through this process improve the care of patients in radiology and radiation oncology. Before these opportunities can be exploited to their fullest, however, the education of medical physicists in the clinical applications of radiology and radiation oncology must be improved. In January, 20–22, 2006 a forum on the physics education of radiologists, radiation oncologists and medical physicists was held in Atlanta. The meeting was hosted by the American Association of Physicists in Medicine, and representatives of 30 radiology, radiation oncology and medical physics organizations attended the meeting. Participants examined the guidelines for education of specialists in all 3 fields, together with expectations of accrediting agencies (eg CAMPEP and ACGME‐RRC) and certification organizations (ABR, ABMP), and developed a number of consensus recommendations on how the various organizations could communicate and work more closely together to improve the physics education of individuals in all 3 specialties. These recommendations will be presented for discussion in this forum, with the purpose of seeking feedback on the recommendations and encouraging implementation of the recommendations in the participants' institutions.
TH‐C‐330A‐01: Data Cube Based Tumor Respiratory Motion Characterization
Authors: Wu Y , Klinginsmith J , Wu H
Published: July 2006

Purpose: Adequate understanding and precise characteristics of tumor motion is essential for accurate radiation dose delivery in real‐time image‐guided radiation treatment. We propose a data cube based approach for representing, analyzing and characterizing tumor motion information at various concept levels. More precise patient clustering and characterization can be achieved by combining the tumor motion information and the patient biomedical information. Method and Materials: Based on a finite state model, a breathing cycle of tumor motion is represented by three line‐segments: exhale (EX), end‐of‐exhale (EOE) and inhale (IN). A data cube is constructed to provide the means of multi‐dimensional data analysis that computes summary information based on arbitrary combination of dimensions. Data navigation methods — roll‐up, drill‐down, slice‐and‐dice — are applied to assist in interactively selecting points of interest and navigating among the concept hierarchy. Patient clusters and motion patterns are detected with the assistance of the visualization tools and advanced data mining techniques, such as K‐means clustering algorithm. In addition, we incorporate the patient biomedical information in this process to obtain more precise patient motion classification and characterization. Results: Experiments have been performed on real patient data. Using our approach, summary information is generated automatically and visually displayed. Patient clustering can be easily detected manually or by clustering algorithms. Interesting motion patterns have been discovered from out preliminary results. More precise patient clustering and motion characterization are accomplished when the approach is used on the combination of motion information and patient biomedical information. Conclusion: The data cube based tumor motion characterization approach not only eliminates all the manual processing on patient motion characterization, but also provides the facility to refine the patient clustering and detect interesting patterns, which will provide valuable input for better understanding of tumor motion and for effective real‐time image guided radiation treatment.
TH‐C‐330A‐04: Novel Learning‐Based Approach to Optimal EPID Image Deblurring and Enhancement
Authors: Roessler P , Maltz J , Somphone O , Blanz E , Gangadharan B , Ghelmansarai F , Morin O , Pouliot J , Bani‐Hashemi A
Published: July 2006

Purpose: Finite focal spot size in X‐ray imaging equipment has a blurring effect on acquired images. For practical reasons, it is neither possible nor desirable to reduce the spot size of medical linacs below a certain diameter. This affects task performance in IGRT, where the blurring of the edges of structures reduces positioning accuracy. Since the focal spot size and shape of linacs vary, the filter must be customized to a particular linac. We have developed an algorithm that learns to deblur portal images by comparing actual images to their Monte Carlo (MC) generated ideal counterparts. Method and Materials: A training object containing sharp edges of all orientations is imaged to capture the blurring and noise characteristics of the system. MC simulations in which a point source irradiates a digital version of the training object are used to generate ideal images. These are used as training data to optimize the convolution kernel that effects deblurring. Owing to the nature of the training data, the kernel will deblur the image as well as enhance edges. We assume since the object is 1m from the source, blurring is uniform for all transverse object planes. Results: Large samples of phantom and patient images were used to evaluate filter performance. A marked improvement in image quality is apparent. Evaluation of spatial resolution (MTF) and contrast‐to‐noise ratio (CNR) reveals a dramatic improvement in MTF but reduction in CNR. However, since the CNR remains above 70 at doses of 1MU, the increase in noise will not effect IGRT task performance. Conclusion: This work indicates the utility of this novel image enhancement technique in clinical images. In particular, visibility of small objects in images, such as prostate seeds, is remarkably enhanced.

Conflict of Interest: Sponsored by Siemens.
TH‐C‐330A‐06: Effects of KVp Setting and Radiation Dose On Calcification Visibility in Cone Beam CT
Authors: Lai C , Shaw C , Meng Y , Chen L , Altunbas M , Tu S , Liu X
Published: July 2006

Purpose: To investigate how the kVp setting and radiation dose affects the detection of microcalcifications in cone beam CT (CBCT). Materials and Methods: Calcium carbonate grains, ranging from 200–212 to 355–425 micron, were used to simulate microcalcifications. The simulated microcalcifications from the same size were arranged to form a 5×5 microcalcification cluster. Each cluster was embedded between two slices of a stacked lunch meat and positioned at the center of each slice of the lunch meat. The lunch meat was then imaged with an experimental CBCT system, which employs a 30 × 40 cm2 a‐Si/CsI based flat panel detector with a pixel size of 194 microns. 300 projection images over 360 degrees were acquired in the non‐binning mode at two kVp setting (60 and 80 kVp) and various doses (4.2, 6, 12, 18, and 24 mGy). The projection images were reconstructed with the Feldkamp algorithm. After that, 767×767×9 volume data were extracted from the CBCT reconstructed images for each MC size group and each dose level as well as each kVp. The images were sequentially displayed on a review workstation with a 1600×1200 CRT monitor and reviewed by six readers independently. The order of the images was randomized for each reader. The readers were asked to count the number of visible microcalcifications. The ratios of the visible microcalcifications were averaged over all readers. Student t‐test was used to compute the p values. Result: For 80 kVp, the images acquired with 4.2 mGy performed similarly to those acquired with 6 mGy (p > 0.05) for each MC size. Additionally, the images acquired with 18 mGy performed similarly to those with 24 mGy (p > 0.05) for most MC sizes.

This work was supported in part by a research grant EB000117 from the NIBIB and a research grant CA104759 from the NCI.
TH‐C‐330A‐08: Soft‐Tissue Detectability Limits in Cone‐Beam CT: 2AFC Tests of Human Observer Performance in Relation to Contrast, Spatial Resolution, and the 3D Noise‐Power Spectrum
Authors: Siewerdsen J , Tward D , Daly M , Paul N
Published: July 2006

Purpose: To quantify the contrast‐detail detectability limits of soft‐tissue structures in cone‐beam CT (CBCT) and to investigate the influence of the plane of visualization (axial/sagittal) and level of prior knowledge on observer performance. Method and Materials: Custom‐built cylindrical phantoms containing spherical lesions of varying size and contrast were imaged on a CBCT bench across a broad range of dose. Two‐alternative forced choice (2AFC) tests were conducted under controlled conditions using 7 observers (physicists and radiation therapists). For each 2AFC test, the proportion of correct responses, Pcorr, was analyzed as a function of lesion size (1.6 – 12.7mm) and contrast (20 – 165HU), dose (2.1 – 6.4mGy), plane of visualization (axial/sagittal), apodization filter (smooth Hanning to sharp Ram‐Lak), and degree of prior knowledge provided to the observer (ranging from Signal‐Known‐Exactly (SKE) to Signal‐Unknown (SUK)). Results: 2AFC analysis provided valuable quantitation of contrast‐detail detectability limits. For example, the lowest contrast lesion (20 HU) was detected at Pcorr>70% for diameters down to ∼6mm at doses >2mGy, but smaller 20 HU lesions (<3.2mm) were barely detectable (Pcorr<60%) at any dose. Detectability was significantly improved in axial versus sagittal planes, and the effect was amplified by sharper apodization filters in a manner consistent with 3D noise‐power spectrum asymmetry. Prior knowledge had a marked influence on detectability — e.g., a ∼6mm (20 HU) sphere was detected at Pcorr∼70–85% for SKE conditions, compared to Pcorr∼55–65% under SUK conditions across the same range of dose. Conclusion: Comprehensive human observer tests provide valuable quantitation of soft‐tissue detectability limits in CBCT and help to define low‐dose techniques for specific imaging tasks. Two factors in particular — plane of visualization and prior knowledge — hold significant practical implications: axial planes typically offer improved detectability, and performance is maintained at significantly lower dose under SKE conditions (e.g., lesion‐known image guidance) than in SUK conditions (lesion‐unknown diagnostic imaging).
TH‐C‐ValB‐02: Clinical Implementation of Cone‐Beam CT for Image‐Guided Radiation Therapy
Authors: Zhu XR , Zhang L , Kudchadker R , Wu R , Balter P , Mohan R , Gillin M , Dong L
Published: July 2006

Purpose: A linear accelerator equipped with cone‐beam CT (CBCT) was commissioned for image‐guided radiation therapy in an IMPAC's Multi‐Access environment. The purpose of this work is to report our experience of clinical implementation of CBCT in a multi‐vendor environment. Method and Materials: The mechanical accuracy of the system was tested using a stereotactic method to verify the imaging isocenter congruent with the therapy isocenter of the accelerator (Trilogy, Varian). Image qualities, including the high contrast resolution (HCR) and low contrast resolution (LCR), were evaluated and compared with the conventional CT (Catphan 600). Imaging doses were measured using TLDs in several anthropomorphic phantoms for the intended treatment sites (head, chest, and pelvis). There are connectivity issues with current vendor provided software, the clinical implementation of CBCT relies on in‐house CT‐assisted targeting (CAT) software, which is used for aligning CBCT images to the planning CT to determine daily setup shifts. The alignment uncertainties and its dependence on imaging dose were verified in phantom with various known couch shifts. Results: The imaging isocenter was found to within 1 mm of the therapy isocenter. The CBCT HCR is similar to the conventional CT, approximately 6∼7 lp/cm, while the LCR is inferior. The CBCT LCR with bow‐tie appears better than without. With bow‐tie, the average imaging doses using built‐in protocols were 7.1, 6.7 and 4.3 cGy in head, chest, and pelvis phantoms, respectively; without bow‐tie, doses were 5.4 and 2.4 cGy for head and pelvic phantoms. Workflow was implemented to use the in‐house CAT software with vendor supplied CBCT acquisition software. The CAT software can predict overall sub‐millimeter accuracy in a phantom experiment with many known couch shifts. Conclusion: We have successfully implemented CBCT for clinical use. Major challenges included various component testing, connectivity, and in‐house software implementations.
TH‐C‐ValB‐03: Quality Assurance Procedure for a KV Cone‐Beam Device
Authors: Bednarz G , Nawaz A O , Xu D , Galvin J
Published: July 2006

Purpose: To establish a quality assurance procedure for kV cone‐beam (CB) devices, and use the procedure to assess the accuracy and precision of a particular CB unit. Introduction: The introduction of the Elekta CB system has created a need for a quality assurance (QA) procedure to test the system's reliability and accuracy and it's alignment with the MV treatment beam isocenter. Materials and Methods: An acrylic phantom with dimensions of 18×19×18 cm3 was used for this work. The phantom included a central slab made of polystyrene that contained two drill holes. One was drilled to the center of the cube, and the other was off to one side and established phantom orientation during scanning. The holes were left open during CT and CB imaging to minimize artifacts. The phantom was first positioned with the center hole at the accelerator mechanical isocenter. Repeated cone‐beam datasets were acquired to determine the system's ability to detect and correct for known table shifts. Finally, the phantom was positioned with CB guidance and the beebee was placed in the center hole. The Winston‐Lutz (WL) test in the phantom was preformed using the electronic portal imager (EPID). The differences between known and CB determined shifts and the WL test analysis were tabulated. Results: and Conclusion: The results showed that the cone‐beam system was capable of determining the shifts applied to the QA phantom to within 0.5 ± 0.4 mm with the largest difference between the known and calculated shift of 1.9 mm. The mean agreement between the kV and MV isocenters was 0.5 mm ± 0.4 mm with the largest deviation of 1.3 mm. This QA study supports a conclusion that the Elekta CB system can be reliably used for positioning of patients with the accuracy in a 1 to 2 mm range.
TH‐C‐ValB‐04: Evaluation of the Quality of 3D‐3D Mutual Information (MI) Shared Between Reference and On‐Board DTS Images
Authors: Godfrey D , Ren L , Yan H , Oldham M , Yin F
Published: July 2006

Purpose: Digital tomosynthesis (DTS) is a fast, low‐dose method for reconstructing 3‐D slices from 2‐D cone‐beam x‐ray projection data acquired with limited source angulation (e.g., 40°). We previously developed a method for reconstructing reference DTS (RDTS) images from a planning CT volume, for registration with on‐board DTS image data. This study examines 3D‐3D mutual information (MI) shared between RDTS and DTS volumes of an anthropomorphic chest phantom. Method and Materials: Planning CT and on‐board CBCT volumes of an anthropomorphic chest phantom were aligned by a point‐registration of 6 metal fiducials. Misregistration (+/− 5mm and +/− 5°) was simulated along each of the six possible translational and rotational dimensions of the planning CT volume. For scan angles spanning 10°–60°, RDTS images were reconstructed from each of the misregistered CT volumes and DTS image sets were computed from actual on‐board projections. 3D‐3D MI between each RDTS and DTS volume was computed for a 4cm × 10cm × 7.5cm central region of interest containing the spine. MI was plotted as a function of each of the six possible translations and rotations, for each DTS scan angle. Results: For all scan angles greater than 10°, residual error in the location of global MI maxima was less than 1.0 mm, and 0.5°. MI resolution to shifts in the depth dimension (normal to individual DTS planes) improved noticeably with increasing scan angle. MI sensitivity to all other shifts and rotations showed only minor improvement with increasing scan angle. Conclusion: MI between planning CT‐generated RDTS and actual on‐board DTS image data is sufficient to be used for rigid‐body registration purposes. The addition of an orthogonal DTS acquisition (i.e., acquiring sagittal along with coronal DTS) is probably unnecessary for rigid‐body DTS registration. Conflict of Interest: This research was supported in part by a grant from Varian Medical Systems.
TH‐C‐ValB‐06: Thoracic Proton Treatment Planning Strategies Based On the 4D CT Information
Authors: Zhang X , Chang J , Liao Z , Komaki R , Cox J , Amos R , Arjomandy B , Kang Y , Wang X , Liu H , Dong L , Mohan R
Published: July 2006

Purpose: Particularly in the case of thoracic radiation therapy, there are substantial inter‐ and intra‐fractional variations in shape, volume and position of treatment targets and the intervening and surrounding normal tissues. The purpose of this work is to develop proton treatment planning strategies for mobile tumors with and without mobile intervening structures based on 4D CT, and to assess the planning strategies using 4D CT data and daily in‐room CT information. Method and Materials: Five treatment planning strategies were evaluated based on (1) free breathing CT with small smearing, (2) free breathing CT with large smearing, (3) average CT with small smearing, (4) average CT with CT numbers inside the tumor volume replaced by higher CT numbers, and (5) maximum intensity projection CT. For a lung patient with large, 1.6 cm, tumor motion and immobile surrounding tissues, treatment plans were designed using strategies 1, 2 and 4. Each treatment plan was recalculated on five daily CT images using bony structure alignment. For an esophagus patient with 3.5 cm tumor motion and large cardiac, liver and spleen motion, treatment plans were designed using strategies 1, 2, 3 and 5. Each treatment plan was recalculated in all 10 phases of the 4D CT. Results: For the lung patient, the tumor coverage evaluated using the five daily CT's is superior when using strategies 2 and 4 as compared to strategy 1. However, the lung sparing is superior using strategy 4 compared to strategy 2. For the esophagus patient, the treatment plans using strategy 2 and 5 covered the targets for each 4D CT phase while the plan using strategy 1 and 3 caused significant under‐dosing. Conclusion: With the strategies developed using 4D CT data, good tumor coverage was achieved for the thoracic patients with large tumor and surrounding tissue motion using proton therapy.
TH‐C‐ValB‐07: Enhanced 4D CBCT Imaging for Slow‐Rotating On‐Board Imager
Authors: Chao M , Li T , Xing L
Published: July 2006

Purpose: Four‐dimensional (4D) cone‐beam CT (CBCT) is currently obtained by respiratory phase binning of the acquired projections followed by independent CBCT reconstruction of the rebinned projections for each phase. Due to the significantly reduced number of projections in a single phase bin, the quality of 4D‐CBCT images is severely degraded. In this work, we develop a technique to combine the data from all phases for greatly enhanced 4D CBCT. Method and Materials: 4D‐CBCT data were acquired with “extremely‐slow‐gantry‐rotation” protocol (1 deg/sec) on a Varian Acuity system. The respiratory phase binning was achieved by automatic texture matching of the CBCT projections, and 4D‐CBCT images were subsequently obtained by Feldkamp reconstruction of the phase‐binned data. Finally, to enhance the quality, the 4D‐CBCT images were superimposed via deformable registration based on maximum mutual information and BSpline model. The method was quantitatively evaluated with numerical and physical phantom experiments. Three clinical cases are also being investigated. Results: The numerical and physical phantom studies showed that 4D CBCT resulted in less motion artifacts than 3D CBCT, however, the view‐aliasing artifacts are visible in 4D CBCT images due to limited number of projections being used for reconstructing each phase, this led to large fluctuation of the CT numbers in any uniform region and generally reduced contrast‐to‐noise ratio (CNR). In comparison, the proposed 4D CBCT technique scientifically improved the CT number accuracy, the image uniformity, and the CNRs. Conclusion: A novel technique for 4D CBCT imaging with a slow‐rotating onboard imager has been developed. It integrates information of different respiratory phases to achieve an enhanced image quality. The improvement on the CT number accuracy is extremely important to image‐guide radiation therapy for online treatment planning and off‐line dose verification.
TH‐C‐ValB‐09: 4D CT Using Retrospective Velocity‐Based Amplitude Sorting
Authors: Nazareth D , Klahr P , D'Souza W
Published: July 2006

Purpose: To present a technique, velocity‐based amplitude sorting (VBAS), which addresses current shortcomings of 4D CT, which is conventionally performed using phase‐based retrospective sorting of CT images. The phase of the breathing signal contains little information about the tumor's displacement. When the breathing signal is irregular, blurring artifacts can result. Amplitude‐based sorting has the disadvantage that fewer images are acquired when the tumor velocity is large, and therefore may reduce spatial resolution. VBAS analyzes the breathing signal to determine the average tumor velocity, and resizes the amplitude‐based sorting bins accordingly. Method and Materials: An infrared marker was placed on the patient's chest and tracked by a camera to record the breathing signal. Each CT image was correlated with the breathing signal and sorted into the appropriate bin using one of three methods: (i) phase sorting, (ii) amplitude sorting, and (iii) VBAS. The 8 resulting image sets for each method were interpolated when necessary. Methods (i), (ii), and (iii) were evaluated by comparing target volumes in reconstructed motion‐phantom images. Volumes of 3 patient tumors were also analyzed to determine their reproducibility over every bin for each method. Results: The volumes of the targets of the motion phantom were compared to those of a static phantom. The respective errors in the methods were (i) 27%, (ii) 34%, and (iii) 11%. The VBAS technique also resulted in the lowest variability in patient tumor volumes: these were (i) 18%, (ii) 32%, and (iii) 12%, respectively. Qualitatively, the spatial resolution of the VBAS images was greatest. Conclusions: Sorting by amplitude rather than phase is advantageous when the breathing signal is irregular. However, to maintain spatial resolution, bin size must be adjusted for tumor velocity, which can be accomplished with VBAS. This method proved to be the most effective in terms of volumetric analysis and reproducibility.
TH‐C‐224A‐02: QA for Linac KV Imaging Systems
Authors: Bissonnette J‐P , Moseley D , Purdie T , White E , Jaffray D
Published: July 2006

The recent commercialization of linac‐mounted kilovoltage imaging systems (i.e., kV systems) has allowed high‐precision verification and correction of patient position immediately prior to the delivery of radiation therapy using fluoroscopic, radiographic, or cone‐beam tomographic modes. This novel technology challenges the radiotherapy community to redefine their patient positioning practice. One can now correct patient position using image information displaying not only bony anatomy and airways, like portal imaging, but also markers and soft tissue structures within the patient, including the target to be irradiated. On‐line kilovoltage imaging further allows, using daily imaging sessions, on‐line correction of patient translations and rotations, and the comparison for successive daily volumetric images permits to track changes of anatomy through the course of therapy. Introducing kV systems within busy radiation therapy clinics requires thoughtful testing and quality assurance protocols (QA) of the device, and judicious modification of existing radiation therapy processes and protocols.

The individual components making up kV systems are well‐established technologies, and the quality assurance for each component follows accepted standards. However, the specific features of the integrated systems require particular attention. First, the kilovoltage beam may not share a common central axis with the megavoltage treatment beam; therefore, the relation of the kilovoltage imaging matrix to the megavoltage treatment beam must be monitored to ensure adequate localization, scaling, and geometric accuracy. Second, cone‐beam tomography differs from conventional or helical CT imaging, and thus encounters specific image quality issues. A well‐planned QA program integrates closely the kV system procedures with linac procedures described in accepted QA standards such as the AAPM task group 40 report.

This lecture will present a brief review of commercial systems, but will focus on a suitable QA program, with special emphasis on issues germane to the system and the clinical processes relying on its use. Examples of clinical use in a number of sites will also be presented.

Educational Objectives:

1. Understand the technical issues related to kV systems.

2. Understand the impact of kV systems on clinical processes.

3. Present a comprehensive commissioning protocol and QA program for kV systems.

This work is supported, in part, by a research grant from Elekta Oncology Systems.
TH‐C‐230A‐03: A Complete MR‐Based Treatment Planning Procedure for Radiotherapy of Intracranial Lesions
Authors: Stanescu T , Jans H S , Stavrev P , Fallone B G
Published: July 2006

Purpose: The purpose of this study is to develop a complete treatment planning procedure for radiotherapy of brain lesions based solely on magnetic resonance imaging. Method and Materials: The MR‐based treatment planning procedure relies on converting the MR images into CT‐like images by assigning electron density information to organ structures (i.e. brain, bone and scalp). First step in the process is to correct the MR images for 3D geometrical distortions by applying a novel distortion correction procedure. The next stage is to segment the datasets into anatomical structures by using an automatic segmentation tool suited for MR brain images. Once the MR images contain both the target volume and the electron density information, they are ready to be used for dose calculations. The resulting CT+MR and MR‐based plans were compared in terms of isodose distributions, DVHs and NTCP/TCPs. A plan ranking TCP‐based method for heterogeneous irradiation, which does not require the knowledge of radiobiological parameters, is used. Results: For all patients investigated, we found that MR‐based plans (1.5T and 3T) are in good agreement (within 1%) with their corresponding CT+MR‐based plans in terms of PTV dose coverage, DVHs and NTCP/TCPs. We compared tumor contours drawn on both 1.5T and 3T MR images in terms of shape, volumes and their impact on CRT plans. For all patients the delineation of the tumor was simpler for 3T images due to higher contrast. For some patients the tumor volumes drawn on the 3T images were up to 60% higher than on 1.5T images. RT plan ranking shows that the 3T plans are significantly better than 1.5T ones. Conclusion: The proposed MR‐based treatment planning procedure was found to perform as good as the current clinical procedure based on CT+MR. Due to a higher contrast the tumor may be significantly better delineated on 3T images.
TH‐C‐230A‐05: Neutron Scattered Dose Equivalent to a Fetus From Proton Radiotherapy of the Mother
Authors: Mesoloras G , Sandison G , Stewart R , Farr J , Hsi W
Published: July 2006

Scattered neutron dose equivalent to a representative point for a fetus is evaluated in an anthropomorphic phantom of the mother undergoing proton radiotherapy. The effect on scattered neutron dose equivalent to the fetus of changing the incident proton beam energy, aperture size, beam location, and air gap between the beam delivery snout and skin was studied for both a small field snout and a large field snout. Measurements of the fetus scattered neutron dose equivalent were made by placing a neutron bubble detector 10 cm below the umbilicus of an anthropomorphic Rando® phantom enhanced by a wax bolus to simulate a second trimester pregnancy. The neutron dose equivalent in milliSieverts per proton treatment Gray increased with incident proton energy and decreased with aperture size, distance of the fetus representative point from the field edge, and increasing air gap. Neutron dose equivalent to the fetus varied from 0.025 to 0.450 mSv per proton Gray for the small field snout and from 0.097 to 0.871 mSv per proton Gray for the large field snout. There is likely to be no excess risk to the fetus of severe mental retardation for a typical proton treatment of 80 Gray to the mother since the scattered neutron dose to the fetus of 69.7 mSv is well below the estimated radiation absorbed dose threshold of 600 mGy observed for the occurrence of severe mental retardation in prenatally exposed Japanese atomic bomb survivors. However based on the linear no threshold hypothesis and this same typical treatment for the mother, the excess risk to the fetus of radiation induced cancer death in the first 10 years of life is 17.4 per 10,000 children.
TH‐C‐230A‐09: Implementation of MINERVA/PEREGRINE as An ATC Review Tool
Authors: Purdy J , Lehmann J , Wessol D , Cogliati J , Milvich M , Frederickson C , Nigg D , Wemple C
Published: July 2006

Purpose: To test the feasibility of a system of software (MINERVA/PEREGRINE) developed by the Idaho National Laboratory (INL) and the Lawrence Livermore National Laboratory (LLNL) for supporting quality assurance (QA) review of cooperative‐group clinical trials treatment planning data within the Advanced Technology QA Consortium (ATC). Method and Materials: MINERVA is an open architecture, open source code system, designed to accommodate any computation engine through a plugin structure. MINERVA supports two types of data storage ‐ relational databases and XML files. Patient data is stored in a relational database. XML‐based import/export tools have been developed to transfer patient information between QA Centers and reviewers. Tools have been implemented as plugins to allow addition of more advanced tools. The research version of the LLNL PEREGRINE Monte Carlo code has been relocated to UC Davis Medical Center. The basis has been created for an integration of PEREGRINE with ITC, and it has been integrated with MINERVA as a calculation engine. Results: MINERVA supports submission of digital treatment planning data using RTOG format. Ability to import DICOM‐RT objects that satisfies the ATC DICOM conformance statement is needed. MINERVA provides display of DVHs and axial patient images with overlaid organ‐at‐risk/target‐volume contours, as well as user‐defined isodose curves. Users can edit contours, recalculate DVHs for these user‐defined structures, and display point doses. Test cases for several body sites have been calculated using PEREGRINE to demonstrate feasibility. We believe that the use of Monte Carlo simulation will become a key tool for credentialing and QA review of clinical trials treatment planning and verification data in the near future. Conclusion: The MINERVA/PEREGRINE software system appears to be well suited to meet the needs regarding QA of data submitted for future ATC‐supported clinical trials. Conflict of Interest: This work was supported by NIH U24 Grant CA81647.
TH‐C‐224C‐02: MicroRT/microRTP: A Conformal Small Animal Planning and Irradiation System
Authors: Stojadinovic S , Hope A , Vicic M , Mutic S , Deasy J , Cui J , Khullar D , Parikh P , Esthappan J , Grigsby P , Low D
Published: July 2006

Purpose: We have developed a novel small animal radiation therapy device (microRT), which integrates multi‐modality imaging, radiation treatment planning, and conformal radiation therapy. In this study, we evaluated the accuracy of the treatment planning and positioning systems of the microRT device. Method and Materials: The microRT system utilizes a clinical 192Ir HDR source collimated via machined tungsten inserts to deliver photon beams at a source to target distances of 1–8cm at four angles (0, 90, 180, and 270). Beams were modeled using Monte Carlo and a parameterized analytic dose engine was created. Radiochromic film (5mm steps) in a solid water phantom was used to evaluate actual delivered doses in multiple planes. Treatment plans using these beams were created by a custom treatment planning system (microRTP) based on imported fiducial‐registered imaging (CT, MR, PET) of animals immobilized in the treatment position. A three‐axis computer‐controlled stage supports and positions animals in the beams according to the microRTP plan. Validation of the positioning system was performed using a phantom and images of phantom and collimator via a kV C‐arm. Results: The analytic dose model agreed with the Monte‐Carlo predicted dose within 5% and 10% outside and inside the 1 mm deep build‐up regions, respectively. Film dosimetry agreed with the analytic model within 10% and also demonstrated an effective field diameter of 8mm at 17mm from the source. The 192Ir line source geometry caused a radial anisotropy of up to 12% at 17 mm depth from the source. The positioning accuracy of the animal support hardware was sub‐millimeter. Conclusions: The microRT system provides conformal radiation therapy based on pre‐treatment imaging and planning for small animal models of cancer and tissue injury.

This work supported in part by NIH R21 CA108677 and by a grant from Varian, Inc.
TH‐C‐224C‐07: EUD‐Assessed Impacts of Respiratory Motion On Breast Irradiation
Authors: Qi X , Lopez F , Driscoll C , White J , Wilson J , Li X
Published: July 2006

Purpose: Respiration results in intrafractional motion and anatomic changes for both target and normal structures (e.g., lung, heart) during the radiation treatment for breast cancer. The purpose of this work is to quantify the dosimetric and radiobiological impacts using the concept of equivalent uniform dose (EUD). Method and Materials: Intrafractional variations were assessed based on 4DCT datasets acquired using a GE LightSpeed‐RT scanner and Varian RPM‐respiratory‐gating system. The 4DCT datasets along with the conventional 3DCT images for 10 patients were analyzed retrospectively. Each set of 4DCT consisted of 10 CT image sets at a phase between 0–90% during one respiration cycle. For each case, a 3D dosimetric plan of two tangential beams irradiating the whole breast was generated based on the 3DCT images using Xio (CMS) planning system. The parameters for this dosimetric plan (e.g., energy, beam angles, beam shape, wedge, weighting, isocenter location) were copied to each phase image set of the 4DCT to generated 3D dose distribution. DVHs for each phase image set were generated and were used for EUD calculation based on LQ model for breast tumor and Lyman model for lung. Results: 4DCT showed breast position/shape and lung position/shape/volume are changed with respiration. For example, lung volume changed up to 20% for the cases studied. These changes result in significant intrafractional variations in dose distributions/DVHs. Our calculations show that, compared to the planned EUD (based on the 3DCT), the breast EUD was lowered by an average of 5% (when including all 10 breathing phases) and up to 10% (at a particular phase). Lung EUD varied by ±3% during respiration. Conclusion: Respiratory motion in breast radiation treatment can potentially result in decreased target coverage and normal structure sparing. This effect that can be assessed using EUD, and decreased EUD may be an indicator for gated breast irradiation.
TH‐C‐224C‐08: Estimating Differences in Volumetric Bone Growth by Treatment Method
Authors: Hua C , Krasin M , Shukla H , Merchant T
Published: July 2006

Purpose: To estimate potential differences in volumetric bone growth in children with sarcoma treated with intensity‐modulated (IMRT) and conformal (CRT) radiation therapy using an empiric dose‐effect model.

Methods: Volumetric bone growth was estimated 4 years after radiation therapy for 36 pelvic bones (ischio‐pubis and ilium) from 11 patients using a random coefficient model for flat bone growth that incorporated patients age, pre‐RT bone volume, integral bone dose >35Gy, and time after completion of RT. Dosimetry representing the actual CRT/IMRT plan, a non‐treated comparable IMRT/CRT plan and an idealized plan delivering dose only to the PTV, with no dose delivered to tissue outside the PTV, were entered into the model and the resultant volumes compared relative to modeled normal bone growth (integral dose of zero). The prescribed dose to the PTV ranged from 36–55.8 Gy and the median values for the PTV and studied bone volumes were 774 ml (147–1964 ml) and 76 ml (14–215 ml), respectively. Results: Relative to normal bone growth, patients were predicted to maintain 93%, 87% and 84% (p=0.06) of their expected growth with idealized, IMRT and CRT approaches, respectively. Older patients, age ⩾10 years were predicted to maintain a mean growth of 98% compared to normal regardless of method. Those age < 10 years maintained 87% (idealized), 76% (IMRT) and 70% (CRT) of expected growth (p=0.015). On post hoc testing (Tukey) CRT and IMRT both differed significantly from idealized but not from one another. Conclusions: Linear dose‐effect models facilitate comparison of treatment methods and potentially interventions. For older patients, treatment methods do not significantly impact growth for specific flat bones; however, for younger patients, treatment methods may significantly impact flat bone growth especially as we move towards idealized dose distributions potentially feasible with particle therapy.