bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐T‐449: Verification of Multi‐Leaf Collimator Position Accuracy Using a Commercial EPID and Vendor Supplied Portal Dosimetry Software
Authors: Taylor M , Lambert M , Harris B
Published: July 2007

Purpose: To develop and implement an efficient QA routine capable of verifying multi‐leaf collimator position accuracy using a commercial EPID and vendor supplied portal dosimetry software. With proper implementation, this routine will provide a rapid technique for detecting minor leaf position misalignments which could result in significant deviation from planned dose distributions for Dynamic delivered IMRT. Method and Materials: A common dynamic MLC leaf position verification test, the Picket Fence, was utilized. This test consists of a series of five continuous 1.0 mm strips, with a separation of 2.0 cm between strips, delivered in dynamic mode. Testing was performed on a Varian EPID aS500 (0.78mm pixel resolution) at 100 cm SSD. A baseline integrated image of the picket fence MLC file was captured. A second picket fence MLC file, with intentional single leaf discrepancies of ±0.2, ±0.3, and ±0.5 mm, was also imaged. Integrated EPID images were first visually inspected for deviations in absolute leaf position and then analyzed with the Varian portal dosimetry software. Within the software, a profile was taken to determine peak intensity between strips, which should have a 2.0 cm separation. Additionally, the profile tool was used to determine peak intensity changes along the length of the 1.0mm strips. These peak intensity changes along the strips can be correlated to leaf positioning errors. Results: All single leaf deviations greater than ±0.3mm were visually recognized and profile analysis confirms that leaf errors of this magnitude produce approximately a 10% change in peak intensity along the 1.0mm strips. Profile analysis did not detect the ±0.2mm error. Conclusion: As noted in relevant literature, leaf position accuracy is of paramount importance for dynamic MLC IMRT delivery. Once a baseline image is validated, these tests can be conducted daily and evaluated in a matter of minutes.
SU‐GG‐AUD‐03: The Development and Validation of An Image‐Based Dosimetry System for 90Y Microspheres Used to Treat Hepatic Tumors
Authors: Selwyn R , Jaskowiak C , Nickles R , McDermott J , Welsh J , DeWerd L , Thomadsen B
Published: July 2007

Purpose: To develop and experimentally validate an image‐based dosimetry system for determining the three‐dimensional (3D) dose distribution from microspheres used to treat hepatic tumors. Method and Materials: A rapid, efficient, and stable batch technique was used to label yttrium‐loaded microspheres with . These ‐labeled microspheres served as surrogates for ‐labeled microspheres. and microspheres were coinjected into a gel‐based phantom and the activity distribution was determined using a GE Discovery LS PET/CT scanner. The activity distribution was converted from to by applying a precise activity ratio, which was determined using germanium detection and a low uncertainty positron branching ratio. To calculate the dose, the image data was convolved with a dose point kernel using 3D‐ID software. This dose was compared to the dose measured in the central plane using HD‐810 radiochromic film and a new film protocol. The film protocol and the gel‐based phantom were validated using a single source seed. The film was calibrated using two NIST‐traceable ophthalmic applicators and was analyzed using a flatbed scanner in reflective mode. Additionally, the image‐based dose to the entire gel phantom was compared to a Monte Carlo‐derived dose. Results: The image‐based (3D‐ID) dose in the central plane was 90.20 Gy ± 6% and the film measured dose was 90.64 Gy ± 5%. A mean phantom dose of 74.30 Gy ± 6% and 74.70 Gy ± 2% was determined using 3D‐ID and Monte Carlo, respectively. Overall, these results agreed to within 0.5%. The image‐based in vivo dose volume histogram (DVH) for this study was in excellent agreement with the film measured DVH. Conclusion: Through the implementation of ‐labeled microspheres, a precise non‐destructive assay of , and a validated film protocol, a new image‐based dosimetry system for microspheres was experimentally validated.
SU‐GG‐AUD‐05: Segmented Crystalline Scintillating Detectors for Radiotherapy Imaging: A Monte Carlo Investigation of Swank Factor
Authors: Wang Y , Antonuk LE , El‐Mohri Y , Zhao Q , Du H , Behravan M
Published: July 2007

Purpose: A systematic theoretical investigation of Swank factor for thick, segmented crystalline scintillating detectors is reported. The Swank noise, originating from variation in the x‐ray‐to‐photon conversion gain, degrades the detective quantum efficiency (DQE) performance of radiotherapy imagers. Therefore, it is of great interest to examine the Swank factor, in particular the optical Swank factor, as a function of various detector design parameters. Method and Materials: Swank factor was investigated using a recently implemented Monte Carlo package (MANTIS) that simulates both radiation and optical transport. The radiation and optical Swank factors were examined using a 6 MV photon beam as a function of various parameters, such as the material and thickness of the scintillator, the element‐to‐element pitch of the detector, as well as the material and thickness of the septal wall separating detector elements. Moreover, the optical Swank factor was examined as a function of the optical properties of the scintillator, top reflector and septal wall. Results: Radiation Swank factor improved when thicker scintillators or higher density septal walls were employed. The optical Swank factor dropped dramatically when the scintillator surfaces facing the walls were not polished. Moreover, the results indicate that septal walls must be highly reflective, as the optical Swank factor was found to drop sharply with decreasing septal wall reflectivity, even for a relatively clear scintillator. Furthermore, the optical Swank factor was also strongly affected by the thickness, absorption and scattering of the scintillator, and modestly affected by the reflectivity of the top reflector. Conclusion: Simulation of radiation and optical transport in segmented scintillating detectors provides the means to examine properties that are critically important to performance, such as optical Swank factor. It is strongly anticipated that such studies will greatly assist in the design of detectors exhibiting very high DQE.
SU‐GG‐AUD‐07: Development of a Novel Detector for Measuring Proton Energy Spectra
Authors: Charara Y , Townsend L , Ramsey C
Published: July 2007

Purpose: The purpose of this study was to design an instrument for measuring proton energy spectra, and present energy deposition results that compare calibration runs with two state of the art Monte Carlo codes, HETC‐HEDS, and GEANT. Method and Materials: The proton energy spectrum analyzer developed in this study is based on a telescope called the Cosmic Ray telescope of the Effects of radiation (CRaTER), originally designed to achieve characterization of the global lunar radiation environment and its biological impacts. It employs a stack of silicon detectors and tissue‐equivalent plastic (TEP) to establish the linear energy transfer (LET) spectra of cosmic radiation relevant for human and electronic parts considerations. Measured and calculated spectra were obtained using dE/dX= (E0−Ef)/L, where E0 and Ef are the energies of the particles as measured by the silicon detectors at either end of each TEP section and L is the length of the material. Results: Results show a very good agreement between experimental and computer models. A comparison of the peak position shows that HETC‐HEDS simulation of the instrument in a clinical proton beam yield a peak at channel 50. In comparison, the peak channel was 55 with Geant and 57 from the MGH data. The reason for the discrepancy is that the HETC‐HEDS analysis was performed for energies down to 0.2 MeV, while the analyses with GEANT and the MGH data included around 20 more energy channels. Conclusion: An LET energy spectrum was designed and computational testing for proton therapy. Comparisons between calibration runs and two simulation runs using GEANT and HETC‐HEDS show promising results in being able to use the instrument for proton therapy calibration purposes. Future investigations will include analyses for different geometrical configurations, as well as investigating the detector's response to other charged particles.
MO‐A‐L100E‐01: Parallel Imaging: Techniques, Quality Control, and Applications (Preview of TG118 Repo
Authors: Clarke G
Published: July 2007

Task Group ♯118 of the AAPM was established to describe the basis of parallel magnetic resonance imaging (pMRI) and its applications to the Medical Physics community. This presentation reviews the aspects of parallel imaging methods that have led to this technology becoming important clinically. The signature enhancement attributable to pMRI is faster MR image acquisition which leads to decreased motion artifact, reduced breath‐hold time, shorter durations of exams or more series acquired per exam. Increased flexibility is also achieved since parallel imaging has distinct advantages for limiting specific absorption rate (SAR) at higher magnetic field strengths.

There are currently two general approaches to pMRI; one based on image‐space reconstruction and the other on k‐space based methods. Details of the design of RF coils, or the entire RF systems, for improving imaging performance in pMRI will be surveyed. Additional benefits may be derived from the use of pMRI in balanced gradient echo imaging, fast spin echo imaging, dynamic MRI, BOLD contrast MRI and diffusion MRI. In addition, the image quality trade‐offs in pMRI will be considered with particular focus on the different ways that signal and noise are handled in pMRI image reconstruction.

Finally advanced results, which will likely lead to continuing improvements in pMRI technology, will be discussed. In summary, this presentation will provide practical guidance and assistance for the practicing medical physicist so that pMRI may be more readily applied and understood within the clinical environment.

By the end of this presentation the attendee should:

1. understand the basic concept of parallel imaging and how it can be used to reduce the acquisition time of MR images.

2. recognize in which clinical protocols the use of parallel imaging methods is most advantageous and what benefits are bestowed on each.

3. be aware of the image quality trade‐offs involved in implementing pMRI and

4. understand the new image artifacts inherent with this approach.
MO‐A‐M100J‐02: Performance Evaluation for New‐Technology CT Systems: 256‐Channel C
Authors: Geleijns J
Published: July 2007

Medical physicists are challenged to assess image quality and patient dose for 256‐channel CT scanners. Whereas current concepts for measurement of image quality still remain valid for 256‐channel scanners, concepts for CT dosimetry will have to change fundamentally. Current methodology for CT dosimetry, e.g. assessment of CTDI with a 10 cm CT ionization chamber and standard CT dose phantoms, is not compatible with the x‐ray beam geometry of the new 256‐channel CT scanner. The beam width exceeds the length of the CT ionization chamber and, at the exit surface of the phantom; the beam width even exceeds the length of the body phantom. Several options to overcome dosimetric problems of cone beam CT scanners will be considered.

Educational Objectives:

1. Understand the design and operation concepts a new 256‐channel axial CT scanner.

2. Understand concepts for specifying and measuring absorbed dose for a new 256‐channel axial CT scanner.

3. Understand shortcomings in current concepts for assessment of absorbed dose and and patient dose for the new 256‐channel axial CT scanner.
MO‐A‐M100F‐01: Integrating the Healthcare Enterprise (IHE) in Radiation Oncology: Will It Help You?
Authors: Curran B
Published: July 2007

Initiated in 2005, Integrating the Healthcare Environment for Radiation Oncology (IHE‐RO) is a multi‐society, multi‐vendor effort to improve the safety, reliability, and integration of computer and information systems within the radiation oncology arena. IHE‐RO works to accomplish this by coordinating the use of standards such as DICOM and HL7 to effectively exchange information between diverse computer systems involved in the process of planning and delivery of radiation therapy treatments. It attempts to remove ambiguity where it exists in these standards by defining consensus profiles to solve real‐world situations.

Each IHE domain (radiology, cardiology, radiation oncology, …) identifies areas where improvements need to be made in the sharing / exchange of information between disparate systems. An IHE Planning Committee then defines a real‐world use case illustrating this process and a trial Integration Profile for improving it. This profile is then discussed by the Technical Committee, which defines the specific standards and methods for exchanging information that will be used to satisfy the needs of the profile and use case. Finally, the Integration Profile and detailed implementation specifics are published in the domain's Technical Frameworks documentation.

Once published, those vendors participating in the IHE process develop / refine products to meet the Integration Profile's requirements. Testing occurs via test tools developed for the profiles and then demonstrated in a formal Connectathon, held under the auspices of the society sponsoring the domain. Companies that successfully demonstrate their compliance with the profile are then included in a public demonstration, held at the society's annual meeting. The complete process from profile initiation to public demonstration typically takes 20–24 months.

In this session, the progress of the IHE‐RO effort will be reviewed. The profile selected for demonstration at the ASTRO 2007 Annual Meeting will be discussed. The proposed profiles for 2008 will be compared, and the rationale for those selected for inclusion in the 2008 demonstration will be given. Profiles developed within other IHE domains, such as Information Technology Infrastructure, will also be discussed.

Educational Objectives:

1. To describe the structure and purpose of the IHE effort, including a brief history of IHE and the formation of the IHE‐RO effort.

2. To review the development process of the 2007 IHE‐RO profile; how it was developed, its benefits, and its limitations.

3. To discuss the profiles currently under consideration for future IHE‐RO efforts, particularly the 2008 public demonstration.

4. To describe efforts in other IHE domains that may influence the development of information systems in radiation oncology.
MO‐SAMS‐L100J‐01: Digital Mammography Update: Design and Characteristics of Current Systems
Authors: Pfeiffer D
Published: July 2007

Mammography still remains the best screening tool for early detection of breast cancer, and the recent ACRIN DMIST results draw attention to the fact that digital mammography is better at detecting cancers in dense breasts. Digital mammography equipment has continued to develop and improve and more vendors and models have entered the marketplace with FDA approval. The technology used in these systems generally falls into four main categories: direct capture detectors, indirect capture detectors, slot scanning, and cassette‐based storage phosphors (computed radiography). Additionally, a photon counting system is being developed. Each of these technologies has its advantages and disadvantages. A review of the systems currently available is presented, including the detector technology utilized. Features of these systems are also presented. This is a Self Assessment Module (SAM) to help fulfill the requirements of the Maintenance of Certification (MOC) process as defined by the American Board of Radiology (ABR). As such, audience participation through interactive questions will be provided during the course of the lecture.

Educational Objectives:

1. Become familiar with the detector technologies currently used in digital mammography systems.

2. Become familiar with the digital mammography systems available from each manufacturer.

3. Become familiar with the unique elements of each system.
MO‐SAMS‐L100J‐02: Digital Mammography Quality Assurance: Comparing the Manufacturers Recommendations
Authors: Berns E
Published: July 2007

Digital mammography is quickly becoming 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 by the FDA different Quality Control tests. 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 review quality control for review workstations and laser printers designed for digital mammography.

Educational Objectives:

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

2. To describe current quality control procedures for review workstations in digital mammography.

3. To describe current quality control procedures for laser printers in digital mammography.

4. To review the impact of QC on ACR accreditation for FFDM systems.
MO‐SAMS‐AUD‐02: Frequencies, Tolerance Limits, and Action Levels for IMRT QA
Authors: Palta J
Published: July 2007

Each intensity‐modulated radiation therapy (IMRT) field includes many small, irregular, and asymmetric fields that completely obscure the relationship between monitor unit (MU) setting and radiation dose. Uncertainty and inaccuracy of dose delivery with IMRT is primarily attributed to the leaf positioning accuracy, modeling of radiation output for small field sizes, modeling of beam penumbra, and the dose outside the IMRT field. Dose‐difference distribution, distance‐to‐agreement (DTA), and a numerical gamma index are often used to evaluate the quality of agreement between measured and calculated dose distributions for the IMRT fields. The tolerance limits based on these indices for IMRT QA are often not adequate because all these methodologies do not account for space‐specific dose uncertainty information. In other words, single tolerance criterion is applied to all test points even when dose uncertainty is significantly different from point to point. At any given point, the dose uncertainty depends on different levels of dose and gradients from multiple small beams rather than that of the overall dose profile. Therefore, new methodologies are needed that determine dose uncertainties based on the dose level and gradient information of each small field.

In IMRT, it is sometimes difficult to have agreement between calculation and measurement of dose at all points in a 3‐D dose distribution. A disagreement at a few points does not necessarily lead to negative overall result if other comparable points are well within the established tolerance limits. We will describe a new approach in establishing tolerance limits and action levels for IMRT QA that will ensure delivery of prescribed radiation dose within an acceptable limit of 5%.

Educational Objectives:

1. To describe the uncertainties in IMRT planning and delivery.

2. To describe the impact of spatial and dosimetric uncertainties on the IMRT dose distribution.

3. To describe the limitations of current methodologies of establishing tolerance limits for IMRT QA.

4. To describe new methodologies for establishing tolerance limits for IMRT QA.
MO‐B‐M100J‐01: Determination of Dose to Individual Patients in Radionuclide Imaging Procedures Including Planar, SPECT, and PET
Authors: Williams L
Published: July 2007

Patient absorbed dose estimation due to internal emitters requires two separate computations prior to using the D = S*Ã formula. Here, D is the desired vector of target organ doses, S is a rectangular matrix of dose per radiodecay and Ã is a vector of cumulated activity curves for the various source organs in the patient. While S may be accessed from tabulations such as the OLINDA program from Vanderbilt University, Ã may be computed only by integrating activity curves A(t) out to sufficiently long times. Several methods are available to determine the activity in a given source organ. One may have tissues or lesions near the surface so as to use inverse square computations. At depth, the observer can use gamma cameras and a geometric mean image (GM), CT assisted matrix inversion (CAMI) or quantitative SPECT imaging. In the latter two cases, hybrid imaging devices such as SPECT/CT make the computations easier since image registration is greatly facilitated. There is also a possibility of PET/CT hybrid images being implemented with the SUV value being used to find the activity at‐depth. Lack of suitable positron labels makes PET studies problematic in the case of a general radiopharmaceutical, however. Errors in activity quantitation are typically on the order of +/− 30%, although they can be much larger in geometrically complicated cases. Two types of S values are commonly used. In type I computations, S refers to a phantom of appropriate size; e.g., adult male or female. Such dose estimates are included in applications to regulatory agencies (e.g. FDA). Additionally, type I results may be used to compare similar radiopharmaceuticals with regard to absorbed dose levels. Both diagnostic and therapeutic radiopharmaceuticals may be of interest. Type II calculations usually refer to a specific patient undergoing internal emitter therapy. Generally, alpha or beta emitters are used in this context. One may use Monte Carlo (MC) methods to find the S or correct tabulated phantom S elements to those approximating the patient. Since therapy involves short‐range emitters, S becomes diagonal and the correction is done via; S(patient) = S(phantom)*organ mass (phantom)/organ mass (patient). Such corrections can be very large — on the order of factors of two‐ or three‐fold. Finally, the uncertainty in the dose values may be estimated by combining errors in both S and Ã.

Educational Objectives:

1. Understand the matrix equation D = S*Ã for estimating internal emitter radiation doses to target organs.

4. Know the various methods to estimate source organ activity.

5. Realize that there are two types of calculations for dose; standard phantom or patient‐specific.

6. Know how to estimate uncertainties in the dose calculation.
MO‐D‐L100J‐02: Automated Propagation of Region‐Of‐Interest Contours Between 4DCT Images Using a Regional Deformable Model
Authors: Chao M , Schreibmann E , Li T , Xing L
Published: July 2007

Purpose: To develop a regional algorithm for contour propagation between difference phases of 4D CT and show its impact on 4D radiation therapy simulation. Methods and materials: The ROI contours were manually delineated on a selected phase of 4D CT on one of the breathing phases by a physician. A narrow band encompassing the ROI boundary was created on the image and used as a compact representation of the ROI boundary. A free form B‐Spline deformable registration was carried out to map the band to other phases of 4D CT. A Mattes mutual information function was used as the metric function and the limited memory Broyden‐Fletcher‐Goldfarb‐Shanno algorithm (L‐BFGS) was employed to optimize the multidimensional metric function. Upon successful registration, the deformation field was extracted and utilized to transform the manual contours to other phases. A bi‐directional contour mapping method was introduced to evaluate the success of the proposed technique. Three thoracic patients with 4D CT scans were used to test the proposed algorithm. Results: A formalism of automated contour mapping has been developed based on a regional narrow band deformable registration. Application of the algorithm to three thoracic patients indicates that clinically satisfactory results are achievable with a spatial accuracy better than 2mm for ROI mappings between adjacent phase, and 3mm between opposite phase mapping. As compared to the conventional whole image‐based registration, the computation here was found to be two orders of magnitude more efficient, in addition to the much reduced requirements in computer memory. Conclusions: A regional deformable registration is an efficient and accurate way for contour mapping and should find widespread application in 4D simulation and treatment planning in the future to maximally utilize the available spatial‐tempo information.
MO‐D‐L100J‐06: Evaluation of An Automatic Algorithm Based On Kernel Principal Component Analysis for Segmentation of the Bladder and Prostate in CT Scans of Prostate Radiotherapy Patients
Authors: Wang P , Lovelock D , Radke R , Jeong Y , Chen S , Mageras G , Amols H
Published: July 2007

Purpose: to evaluate the performance of an automatic segmentation algorithm used to segment the prostate and bladder in CT scans of patients undergoing external beam radiotherapy. Method and Materials: A nonlinear kernel principal component analysis (KPCA) based algorithm has been developed to model the surface shapes of soft tissue organs in the pelvis of prostate patients. A library of 25 patients, each with approximately 13 CT scans acquired during their treatment, has been manually segmented by a physician. The library is used to both train and evaluate the algorithm. In this preliminary analysis, the training sets consisted of the contours from 8 to 10 scans of a single patient. Evaluation was performed using 3 CT studies previously unseen by the system from each patient, from the beginning, middle and end of treatment. Performance was measured by comparing the volumes and center‐of‐gravity positions of the generated surfaces with those of the physician‐drawn surfaces. The prostate shapes were also compared by generating maps of the surface separation after center‐of‐mass alignment. Three models were evaluated: a prostate‐only model, a bladder‐only model, and a joint prostate‐bladder model. Results: All models demonstrate the ability to successfully segment the soft tissue structures in the majority of cases. The average ratios of the prostate and bladder overlap volumes to the references volumes for the first seven patients were found to be 0.829 and 0.868 for the prostate only and bladder only models. The joint model results are similar, the corresponding ratios being 0.853 and 0.844. Surface separations for the two models were similar, the models generally being within 1 mm of the physician‐drawn shapes at mid‐organ, and along the right and left sides. Conclusion: Preliminary results from the proposed automatic segmentation method indicate it is sufficiently accurate for radiotherapy applications.
MO‐D‐L100F‐02: Nanotube Based Multi‐Pixel Field Emission X‐Ray for CT and Radiotherapy
Authors: Zhou O
Published: July 2007

Purpose: To develop a new field emission x‐ray source with multi‐pixel and multiplexing capability for high speed computed tomography Method and Materials: The new x‐ray source utilizes the carbon nanotubes (CNTs) as the “cold cathode” to replace the thermionic cathode used in the conventional x‐ray tube. The x‐ray tube current is generated by applying an external electrical field to extract the electrons from the carbon nanotubes. By controlling the triggering signal, x‐ray radiation with programmable waveforms can be readily generated. One‐ and two‐dimensionally pixilated x‐ray source with spatially distributed focal spots is constructed by using a matrix addressable multi‐pixel CNT cathode. The electronics for controlling and integration of the x‐ray source have been demonstrated. Results: A new x‐ray source based on the CNT field emission technology has been developed. The x‐ray source is capable of generating the flux, energy and spatial resolution required for medical imaging. A micro‐focus x‐ray source with 30–50μm isotropic focal spot size has also been developed. A micro‐CT scanner using the field emission x‐ray source was constructed for imaging for small animal models with respiratory and cardiac gating capability. The results from preliminary studies will be discussed Conclusion: The CNT based field emission x‐ray source offers unique capabilities that are attractive for high speed CT imaging such as spatially distributed x‐ray pixels. It enables collection of multiple projection images from different viewing angles without mechanical motion either sequentially or simultaneously which can potentially lead to stationary gantry‐free CT scanners for high resolution and high‐speed imaging.
MO‐D‐M100F‐01: Emerging Techniques Using Digital Tomosynthesis
Authors: Yin F
Published: July 2007

In‐room radiolographic imaging systems is being rapidly implemented in routine clinical operations for target localization. A typical system consists of a kV x‐ray source and an amorphous‐silicon flat panel detector mounted orthogonally to the MV‐beam axis. The available clinical imaging capabilities from this configuration are 2‐D radiographic or fluoroscopic imaging and 3‐D CBCT. These techniques may have potential limitations either on not sufficient anatomical information for positioning verification (such as 2‐D technology) or long imaging time (several breathing cycles), mechanical constraints, and excessive dose to the imaging volume (such as CBCT technology). Therefore, limited‐angle digital tomosynthesis (DTS) is being investigated as an alternative 3‐D imaging technique. Much of the investigations have been focused on the clinical feasibility and efficacy of using DTS for on‐board target localization and comparison between DTS technology with 2‐D radiographic and CBCT technologies. This talk will summarize emerging clinical research to develop the DTS technology for on‐line patient positioning and target localization for image guided radiation therapy, specifically for anatomical sites of head and neck, abdomen, breast and prostate.

Educational Objectives:

1. Brief review of DTS imaging technique in the treatment room.

2. Clinical feasibility and efficacy of using DTS for in‐room target localization.
MO‐D‐M100F‐04: In‐Room Imaging for Treatment of Lung and Breast Cancer
Authors: Galvin J
Published: July 2007

New in‐room IGRT techniques for treatment of targets in and around the lungs allow margin reduction compared to the use of more traditional MV radiographic verification techniques. Unlike targets in the head & neck, liver or prostate, the lung is interesting in that tumors are frequently easily visualized so that the use of surrogates is not always necessary. This is particularly true for volume imaging devices that can produce thin sections through the patient in various different orientations. These devices include diagnostic quality helical CT scanners placed in the treatment room in close proximity to the treatment unit as well as various MV or kV Computer Tomography approaches that use the capabilities of or simply attach to the treatment unit structure. Devices that use kV photons to produce dual stereoscopic 2D views of the patient do not allow such easy visualization of lesions in the lungs, but they are extremely helpful when reliable anatomic surrogates can be identified, or when fiducial markers can be surgically placed to identify the target position.

Hypofractionated dose schedules are gaining popularity for treatment of some early diagnosed non‐small cell lung cancers. Treating these tumors to a high dose in just a few fractions is challenging in that field placement is critical. In‐room IGRT has played an important role in positioning these treatment fields with the required accuracy. Treating the breast, another structure in the thorax region, presents a somewhat different challenge in that this part of the patient's anatomy is hard to reproducibly position for each day of treatment. In‐room IGRT can also be used to advantage to treat this structure. This is particularly true for the boost portion of the treatment.

Treating in or near the thorax is complicated by the fact that targets can move as a result of respiratory and/or cardiac motion. When breath hold, abdominal compression to damp a tumor's trajectory, target tracking, or treatment unit gating techniques are employed to control the effects of respiratory motion, using IGRT to verify patient positioning prior to treatment will not necessarily guarantee acceptable tumor targeting during dose delivery. However, the use of real time in‐room kV and MV fluoroscopy can provide extra information that is useful for this level of verification.

Using the new IGRT techniques does not assure that apertures are correct in terms of either their shape or orientation. Thus, it is important to combine the new IGRT techniques with the older standard approach. That is, portal imaging using the MV beam and treatment apertures remains an important step in the overall QA process.

1. To understand the design, functioning, advantages, and limitations of the different IGRT systems used for treating in and around the thorax region.

2. To understand how different IGRT systems can be used to provide the information needed to target moving lesions in the thorax region.

3. To understand the workflow issues for IGRT used to treat targets in the thorax.
MO‐D‐M100F‐05: Latest Clinical Development for H&N and CNS
Authors: Wu Q
Published: July 2007

Daily target localization is a critical step to ensure accurate delivery of 3‐D conformal radiation therapy and intensity‐modulated radiation therapy. Current in‐room localization technologies for HN and CNS treatment include 2D kilovoltage (kV) or megavoltage (MV) radiography, CT on‐the‐rail, cone beam CT (CBCT), megavoltage CT (MVCT), and optical guidance systems.

This lecture will provide an overview of the current in‐room target localization technologies for HN/CNS treatment, including the system design and characteristics, patient alignment process, and their integrations in clinical workflow. The accuracies of these technique and consequently the margin considerations will be discussed.

Educational Objectives:

1. Understand the latest commercial available in‐room localization techniques for HN treatment.

2. Understand the accuracies of these localization systems.

3. Understand the margin considerations associated with using these systems.
MO‐D‐AUD‐01: A Comprehensive Study On the Heterogeneity Dose Calculation Accuracy in IMRT Using An Anthropomorphic Thorax Phantom
Authors: Davidson S , Popple R , Ibbott G , Followill D
Published: July 2007

Purpose: To provide a comprehensive study on the accuracy of many commonly used Intensity Modulated Radiation Therapy (IMRT) treatment planning systems using the Radiological Physics Center's (RPC) anthropomorphic thorax phantom. Method and Materials: Treatment planning systems (TPSs) from Corvus, Eclipse, Pinnacle, and Tomotherapy were evaluated using the RPC anthropomorphic phantom. Treatment plans were designed using the same clinical constraints and prescriptions so that 96% of the planning target volume (PTV) was covered by the prescription dose. The phantom is equipped with TLD located in the tumor, heart, and spinal cord and radiochromic film located in three anatomical planes intersecting the tumor center and extending into the lung. IMRT QA was performed to adjust the calculated dose distributions in order to isolate the effects of heterogeneity. Comparisons were made between each TPS calculation and measurement. In two instances, re‐calculations of the original correction based pencil beam (PB) plans were performed using the superposition convolution (SC) method. Results: TPSs employing superposition convolution algorithms predicted dose within 3.6% of the target TLD, while TPSs using correction based pencil beam algorithms predicted dose within 5.0% of the target TLD. Both algorithm types showed variations (2% to 38% in the cord and heart) in predicting low dose to normal structures. The dose distributions within the PTV and penumbra lung regions showed good agreement when using an SC algorithm. However, TPSs using the PB type algorithm overestimated dose in the PTV and underestimated the extent of penumbra broadening corresponding to the surrounding lung. Conclusion: This work demonstrated that superposition convolution algorithms found in widely used IMRT treatment planning systems are able to calculate the dose accurately to the PTV and penumbra regions when low density heterogeneities are involved. Conflict of Interest: This work supported by PHS CA010953 and CA081647 awarded by NCI, DHHS.
MO‐D‐AUD‐03: Verification of Lung Tumor Doses Calculated by the Eclipse AAA and Pinnacle CC Algorithms
Authors: Aydogan B , Tiryaki H , Al‐Hallaq H , Roeske J
Published: July 2007

Purpose: The goal of this study was to investigate the dosimetric accuracy of the analytical anisotropic algorithm (AAA) for the treatment of lung tumors. This algorithm, recently implemented in Eclipse (Varian Inc., Palo Alto, CA), was also compared to the Pinnacle's (Philips Medical, Cleveland, OH) collapsed cone (CC) algorithm. Methods: Four phantoms were used in this study. Three lung‐, bone‐ and water‐equivalent slab phantoms were designed to validate the accuracy of the calculated doses in simple geometries. Doses were additionally measured in the CIRS (Norfolk, VA) thorax solid water phantom, which includes lung cavities and a cylindrical spine. All four phantoms were CT‐scanned with thermoluminescent dosimeters (TLD) in place. Plans were generated with the AAA algorithm using anterior‐posterior (AP), AP/PA, oblique, and intensity modulated (IMRT) beams with both 6MV and 18MV photons. The dose distributions for all plans, excluding the IMRT, were re‐computed with Pinnacle using monitor units matched to the AAA plans. Dose measurements were performed with TLDs and ion chambers at 6 different positions including three in tissue, one in spinal cord, and two in lung. Results: The AAA algorithm was found to calculate the dose in lung and tissue accurately to within 6% in all four phantoms. Ion chamber measurements showed 2–3% better agreement than the TLDs in the thorax phantom. For 6 MV, the differences between measured and calculated doses were less than 2% for both AAA and Pinnacle for all six points. However, for the 18 MV beam, the dose measured in the spinal cord was 5.9% greater than the calculated dose with both algorithms. Measured and calculated doses agreed to within the 2% for the IMRT plan. Conclusion: The AAA algorithm provides accurate dose calculations in and around heterogeneities, similar to that provided by the CC algorithm implemented in Pinnacle.
MO‐D‐AUD‐07: Determination of Output Factors for Stereotactic Radiosurgery Beams by Monte Carlo and Measurements
Authors: Fan J , Paskalev K , Li J , Wang L , Chen L , Price R , Jin L , ElDib A , Ma C
Published: July 2007

Purpose: The Varian Trilogy accelerator provides high dose rate (1000MU/min) photon beams for stereotactic radiosurgery (SRS). Different output factors have been reported and their use may impair observations of dose response and optimization of prescribed dose. In this work, we investigated the output factors for the Trilogy 6 MV SRS beam using Mote Carlo simulations and measurements. Method and Materials: The Trilogy SRS cone collimators are 5 mm to 30 mm in diameter. Chamber measurement of output factors is difficult for small cone sizes. In this work, the measurement was carried out using a 0.015cc pinpoint chamber and Gafchromic EBT film. The Monte Carlo simulation was performed using the MCBEAM/MCSIM codes for linac head simulation and phantom dose calculation. The Monte Carlo calculations were validated using the measurement results and compared with the Varian recommended beam data. Results and Conclusions The agreement in percent depth doses and dose profiles between the simulation results, the measurement results and the Varian data was within 2%/1mm for the 10×10 cm2 reference field and all the cones at a 100 cm source to surface distance. The output factors obtained from the Monte Carlo simulations were in excellent agreement with the values from the film measurements. Similar agreement was found between the Monte Carlo results and the pinpoint chamber values except for cones with diameter less than 20 mm where the 2 mm chamber diameter has become comparable to the field size. However, the Varian recommended output factors are consistently higher than the Monte Carlo results, especially for the 5 mm cone, where the difference reaches 10.9%. Therefore, great caution must be taken with the use of the Varian recommended beam data.
MO‐D‐AUD‐08: Dose Verification at the Surface of Air Cavities During Radiation Therapy Using the TomoTherapy Hi‐Art System
Authors: Schoen A , Gerbi B
Published: July 2007

Purpose: Air cavities are a significant inhomogeneity in radiation therapy. TomoTherapy, a helical dose delivery system, is dependent on a heterogeneity based treatment planning system. Plan optimization can be affected by changing the pitch of treatment delivery along with the modulation factor for the treatments. The system allows for calculations using a fine, normal, or coarse calculation grid. In this investigation, we assess the dose delivered to the surface and superficial regions of the cavity, the influence of the above parameters on dose delivery, and the accuracy of the planning system to represent the dose in these regions. Method and Materials: Four different 3×3 cm2 air cavities configurations in solid water were investigated‐with 9 and 1cm solid water above the cavity, with the cavity open at the surface, and with no cavity to measure the surface dose. Each cavity had a reference plan, two plans changing pitch, and two plans changing modulation. We compared the predicted dose to measured dose using both the Attix chamber and TLD powder. Results: A large variation in the percent difference between measured and expected dose depends on the location of the air cavity below the phantom surface. The accuracy of the delivered dose varied with both modulation factor and pitch dependent on the cavity location in the phantom. The Attix chamber and TLD powder showed essentially the same response, but the Attix chamber data was more precise. Conclusions: The accuracy of the delivered to expected dose on the cavity surface was greater when the air cavity was far below the surface (0–5%). As the cavity moved closer to the surface, the deviations in measured to expected dose increased to minus 40–50% of the measured dose at the surface.
MO‐D‐M100J‐02: Trajectory Based Radiation Therapy
Authors: Otto K
Published: July 2007

Purpose: To develop a time efficient IMRT delivery platform that simultaneously exploits all mechanical degrees of freedom of the linac. Method and Materials: Trajectory Based Radiation Therapy (TBRT) is a new technique for planning and delivering optimized dose distributions where the radiation source moves along a continuous 3‐dimensional trajectory defined by gantry angle, couch angle, and couch position. The trajectory is constructed using a series of control points distributed along the trajectory. For planning, continuous source motion is modeled as a series of static beams with one beam defined at each control point. Highly restrictive constraints are placed on MLC and source motion to preserve a continuous, efficient and accurate delivery. Normally these restrictions would also severely limit the ability of the optimization algorithm to derive a high quality plan. This problem is solved using a novel technique for aperture based optimization where a coarse sampling of unrestricted control points is used in the initial stages of optimization. As the optimization progresses additional control points are added with increasing restrictions on MLC and source motion. This approach maintains time efficiency and delivery accuracy while allowing the optimization to derive a high quality plan. Results: Time studies have shown that TBRT delivery times are reduced to ∼ 1.5 to 3 minutes for a 200 cGy fraction. Thus far, results have shown that treatment plans generated with TBRT have dose distributions that are equivalent to or superior to static gantry IMRT. Conclusion: On‐line imaging techniques have provided clinicians with tools for verifying patient position and adapting treatment plans but at the expense of increased treatment time. TBRT is well suited for on‐line verification and adaptation with delivery times that are substantially shorter than static gantry IMRT, IMAT and Tomotherapy. Conflict of Interest: Supported in part by Varian Medical Systems.
MO‐D‐M100J‐04: Exploiting Dosimetric Margins to Reduce IMRT Treated Volumes
Authors: Gordon JJ , Siebers JV
Published: July 2007

Purpose: To develop an IMRT optimization strategy in which CTV‐to‐PTV margins are iteratively reduced until the dosimetric margin distribution (DMD) meets a 90% population coverage criterion (PCC), with coverage being the percent of patients for which the CTV minimum dose is 100% or more of the planned PTV minimum dose. Method and Materials: The DMD is the 3D margin distribution between the CTV and the treated volume (TV). Consistent with ICRU guidelines, the TV is the volume enclosed by the PTV minimum dose isodose surface. Optimization utilizes an iterative approach which converges on a DMD that exactly meets a 90% PCC. In each iteration, the DMD is obtained by exporting the CTV and TV as meshes, and calculating the margins between them via a computational geometry package. Coverage with respect to the PCC is computed based upon the DMD. In the next iteration, the PTV is re‐created using a CTV‐to‐PTV margin determined via linear interpolation from prior coverage estimates to move the plan towards the desired PCC. Intensities are then reoptimized, and coverage is re‐evaluated. Iterations continue until the 90% PCC is met. Results: The proposed algorithm was run for a prostate IMRT plan. For 2mm simulated random and systematic setup errors, the algorithm yielded 3mm CTV‐to‐PTV margins, less than the 6.4mm margin prescribed by the van Herk margin formula (VHMF). While the DMD maintained the desired 90% coverage, the TV was reduced by 63% relative to a VHMF CTV‐to‐PTV margin plan. Conclusion: To accommodate patient setup errors in a self‐consistent manner, it is feasible and desirable to generate IMRT plans in which the DMD meets a population coverage criterion. DMDs assure the desired PCC is achieved and can result in lower treated volumes compared with traditional margin approaches. (Work supported by NIH R01CA98524).