Volume 36, Issue 6, June 2009
Index of content:
- Practical Medical Physics: Room 213A
- ACR Accreditation in Nuclear Medicine and PET ‐ A Practical Guide
36(2009); http://dx.doi.org/10.1118/1.3182243View Description Hide Description
The American College of Radiology's (ACR) Nuclear Medicine and PET Accreditation Programs evaluate qualifications of personnel, equipment, image quality, and quality control measures. It is believed that these are primary factors that impact the quality of patient imaging. The ACR accreditation allows facilities to critique and improve their practices as part of their preparation for the accreditation evaluation process. The goals of the ACR Nuclear Medicine and PET Accreditation Programs are improvement in the quality of imaging, provision of educational information by raising awareness of imaging issues, and the recognition of imaging facilities which meet program objectives. This presentation will outline the program requirements, highlighting some of the common pitfalls that may cause deficiencies in both the clinical and phantom submissions.
This presentation will provide participants with:
1. General information describing the ACR Accreditation Programs
2. Information about the Diagnostic Modality Accreditation Programs
3. Specific information about the ACR Nuclear Medicine and PET Accreditation Program, to include the application process, clinical images submission and quality control requirements.
36(2009); http://dx.doi.org/10.1118/1.3182244View Description Hide Description
This lecture will present a review of the specific aspects and requirements of the nuclear medicine accreditation process. Particular emphasis will be placed on the process for SPECTcameras. The specifics of the phantoms, acquisition procedures, and the review of submitted data will be presented. Examples will be given for specific cameras. Upon completion of the course participants will be able to describe:
1. The characteristics of the required ACR phantom for SPECT.
2. The acquisition procedures used for accreditation in nuclear medicine.
3. The image characteristics evaluated by the ACR phantom reviewers.
36(2009); http://dx.doi.org/10.1118/1.3182245View Description Hide Description
PET scanner accreditation is based on reviews of images acquired from the ACR PET phantom. The phantom is relatively easy to fill and set up for a PET study and can be used to measure tomographic uniformity, spatial resolution, and the detectability of “hot” lesions. The variety of resolution and “hot” components enables the reviewers to see relatively subtle differences in system performance.
The accreditation phantom images are submitted to a review panel of qualified medical physicists for scoring. The Nuclear Medicine Accreditation Committee has defined acceptable standards for uniformity, spatial resolution and lesion detection.
Uniformity and noise are evaluated qualitatively by inspection of reconstructed tomographic sections. Optimal density ranges should be comparable to those used for clinical images.Spatial resolution is judged by identifying the smallest “cold” rods in the phantom and lesion detectability is determined from the “hot” cylinders. The same protocol is also used for the “cold” cylinders that demonstrate the effectiveness of the attenuation and scatter corrections.
1. Be aware of the ACR PET accreditation process and PETPhysicist Qualifications.
2. Understand the ACR PET Phantom and testing required for ACR accreditation.
3. Understand how phantom images are reviewed by the ACR.
4. Be able to activate the ACR Phantom.
5. Understand phantom image acquisition and processing.
6. Understand PET phantom imagecontrast, resolution, and uniformity.
- Using and Contributing to Shared Quantitative Imaging Resources
MO‐E‐213A‐01: NCI: Quantitative Imaging Initiatives and Public Resources for Standarized Data Analysis36(2009); http://dx.doi.org/10.1118/1.3182274View Description Hide Description
NCI has developed a number of research initiatives to help promote more standardized methods for the measurement of drug or therapy response using quantitative imaging. These initiatives include the following:
1. PAR 07 214: (R01) Industry Academic Partnerships.
2. PAR 08 225 (U01): Quantitative Imaging Network (QIN)
3. RFA 08 225 (U54): Multi Modality Imaging Platforms
4. SAIC Contracts: Data collections for RIDER project
These initiatives involve the development of public resources for sharing image data and results of measurements that includes repeat and longitudinal measurements for phantom and clinical data for a range of imaging modalities (CT, PET CT, DCE MRI, DW MRI and optical imaging). This presentation will describe these resources and how they can be used to support more standardized quantitative imaging methods. In addition a review of recent juried consensus publications for how to use these NCI resources will be addressed. Finally NCI ongoing efforts to support the efforts of different imaging societies such as the RSNA (QIBA), AAPM, SNM and ISMRM will be presented.
1. Understand NCI initiatives for quantitative imaging
2. Understand how to use the public resources to promote imaging standards
3. Understand the importance of quantitative imaging as a biomarker for therapy related clinical trials.
36(2009); http://dx.doi.org/10.1118/1.3182275View Description Hide Description
Although it may appear relatively straightforward to extract quantitative metrics from static or dynamic imaging data, a variety of details are critical to the establishment of a data acquisition,analysis, and interpretation methodology that can significantly influence the fidelity of a clinical or fundamental investigation of imaging as a biomarker. While typical users will find available commercial tools and apply them, understanding these fundamental steps will help both the local investigator as well as national efforts to standardize the methodologies and understand the limits of information that can usefully be extracted by a given technique. As an example, the use of MRI‐based Dynamic Contrast Enhanced (DCE‐MRI) imaging and analysis of perfusion‐related metrics is described. The optimization of an image acquisition protocol, which varies by the tissue being studied, is presented. The steps to process this temporal data are described, including image registration for analysis of intrahepatic perfusion. The variables typically associated with DCE analysis, including Ktrans , blood flow, blood volume, and mean transit time, are defined. The dependence of these variables on image quality and temporal sampling are briefly mentioned. The step‐by‐step analysis of the data to extract regional information is presented. An example paradigm relating the analyzed metrics to external variables (e.g. local radiation dose) is shown.
1. To understand practical issues to extract quantitative imaging metrics
2. To understand how to increase robustness and objectiveness in the analysis
3. To understand limitations of derived quantitative imaging metrics
MO‐E‐213A‐03: The Cancer Biomedical Informatics Grid — A Tremendous Resource for Research and Clinical Care36(2009); http://dx.doi.org/10.1118/1.3182276View Description Hide Description
The cancerBiomedical Imaging Workspace is a part of the National Cancer Institute's caBIG initiative which is an effort to utilize grid computing and well defined standards to create a semantic web for exchange of research and clinical information including proteomic,genomic, laboratory, clinical, and imaging data. The Imaging Workspace consists of experts from the diagnostic imaging and radiology oncology communities across the United States with a wide variety of different areas of expertise. The purpose of the workspace is to identify and address challenges in the exchange and cross‐correlation of images and related information including imagevisualization and processing and analysis algorithms for research and secondarily clinical applications. The current major projects of the workspace include an effort to create a standard for annotation and image markup (AIM), a set of tools to facilitate the creation of applications that utilize the DICOM working group 23 standard (application hosting), middleware to create software bridges between DICOM and grid computing protocols and an algorithm validation toolkit which represents a resource for validation of a wide variety of imaging algorithms. The NCI has also created a free and open source DICOM image archive designed as a research repository for clinical trials that can also be used for a variety of other purposes. The Vasari Project represents a project which integrates the imaging workspace tools and is designed to allow correlation of MRI studies in patients with brain tumors with genomic and clinical data in a demonstration project of the potential role of diagnostic imaging in personalized or stratified medicine.
1. Understand the goals and objectives of the NCI's caBIG imaging workspace
2. Be able to list the major projects of the imaging workspace
3. Describe how the Vasari project will integrate the workspace projects in an initiative to allow cross correlation of image data with associated genomic, laboratory, and clinical data
- Routine Testing of CR and DR Radiographic Systems
36(2009); http://dx.doi.org/10.1118/1.3182363View Description Hide Description
Development of standards for performance verification of digital radiographic systems has been outpaced by commercialization of the technology. Practitioners, operators, vendors, and medical physicists are uncertain as to how to configure, calibrate, and verify systems for the best diagnostic quality images at the lowest practical radiation exposure to the patient. Several manufacturers have fielded commercial systems for performance verification, but long term data indicating trends and action limits is rare. Sources of definitive information on practical clinical methods are also scarce in the scientific literature. This has led to the current situation where clinical imaging operations are routinely conducted using systems that are not optimized.
This workshop will discuss four important aspects of traditional medical physics practice that are modified when dealing with DR systems. These processes are of primary importance to medical physicists, because they affect both the quality of DR images and the ionizing radiation dose to patients. First, we consider how to perform an inspection on a radiographic unit using CR or DR. Second, we discuss how to set up the AEC for CR or DR exams. Third, we address how to verify the exposure indicator for CR and DR. Finally, we discuss available phantoms and their characteristics and limitations when used with DR.
1. Understand how some conventional tests should be modified for a digital radiographic system that is integrated into an electronic image management system.
2. Identify key references and standards that can be useful in testing of DR.
3. Appreciate opportunities for improvement of testing of DR systems.
- Code of Practice for the Proton Therapy System
36(2009); http://dx.doi.org/10.1118/1.3182402View Description Hide Description
In the last few years, proton therapy systems (PTS) have become commercially available for routine clinical use. This development promises a new interest in conformal therapy and poses a challenge to a radiationoncology team to develop methods that ensure safe and efficacious use of this new technology.
The uses of protons for radiation therapy require greater expertise of all involved in their use: radiationoncologists,physicists,dosimetrists, therapists and supporting technical staff. The operation, control and quality assurance of PTS often involves a considerable degree of computerized control and data processing techniques. For all practical purposes, acquisition of such equipment requires making a choice between a limited numbers of commercially available FDA approved PTS. Nevertheless, the radiationoncology team that is ready to purchase a PTS is faced with the complex task of selecting the appropriate machine from those commercially available and developing a code of practice for its safe clinical use. The selection, installation, and clinical use of PTS involve:
1. development of the specifications of the proton therapy system, which should be based on;
a. a careful study of the clinical needs;
b. a careful study of technical and physical specifications of the commercially available equipment, including the technical and operational characteristics of the essential accessories;
c. available or needed physics or therapy staff, and available in‐house technical support;
d. an analysis of the financial implications, including warranties and the possible need for maintenance contracts;
2. design and construction of the facilities to accommodate the selected PTS, including radiation shielding;
3. installation of the selected PTS; verification of radiation safety in the environment of the radiation facility;
4. acceptance testing of the installed equipment;
5. commissioning of the PTS for active clinical use;
6. training of the staff in the safe and efficacious use of the PTS;
7. development and application of a comprehensive quality assurance (QA) program.
The focus of presentations is to, a) describe the process of acceptance testing and clinical commissioning b) discuss the clinical workflow for different disease sites and c) describe strategies to optimize the utilization of the PTS.
1. understand the process of developing specifications,
2. learn acceptance test procedures
3. understand clinical commissioning of a PTS
- Clinical Implementation of Newer Technologies
36(2009); http://dx.doi.org/10.1118/1.3182436View Description Hide Description
The Leksell Gamma Knife_ Perfexion_ is the latest gamma stereotactic radiosurgery (GSR) unit manufactured by Elekta (Elekta Instrument, AB, Sweden). Introduced in 2006, it is substantially different in design and operation from previous Gamma Knife (GK) models. The major differences are in the collimation system, the configuration of the radioactive 60Co sources, and in the patient positioning system. The Perfexion_ has one fixed tungstencollimator containing 576 different collimating channels, whereas older GK models have one primary collimator, located inside the unit, and 4 interchangeable secondary collimators that are mounted manually. In the Perfexion_, 192 60Co sources are situated on 8 moveable sectors (24 sources per sector), that slide over the collimator placing the sources over the planned collimating channels to deliver the desired radiation shot size. In older GK models, by contrast, 201 60Co sources are fixed in space and arranged in a pseudo‐hemispherical configuration. Finally, for the Perfexion™ the treatment table, which moves with sub‐millimeter accuracy in three orthogonal directions, is the patient positioning system. For older model GK units, patient positioning is accomplished by attaching the Leksell stereotactic frame to the secondary collimator via specialized hardware called trunnions or via the automatic‐patient‐positioner (APS).
The specific goals of quality assurance (QA) for gamma stereotactic radiosurgery include determining the dose rate for the largest available collimator, measuring the relative output factors and beam profiles for each collimator size and comparing the results to those used in or calculated by the treatment‐planning program, and verifying that the radiation focal point coincides with the center of the patient positioning system. Although these QA tasks for GSR units have remained essentially unchanged over the years, new tools and protocols designed for linear accelerator QA have become available that can be applied to QA for GSR devices. With this in mind, a new AAPM Task Group (TG‐178) has recently been formed and charged with updating QA procedures for older GSR devices that have static sources, creating new QA protocols for GSR devices that are characterized by moving sources, and suggesting a protocol for ionization chamber calibration specific to GSR devices.
This lecture will describe the operation of the Leksell Gamma Knife_ Perfexion_ and the unique features of QA for GSR units, with emphasis on the Perfexion_. Some of the questions faced by TG‐178 will be discussed, old QA procedures will be reviewed and possible new QA tests will be suggested.
1. Review QA requirements for GSR units
2. Understand the design differences between older GK models and the Perfexion_ and the implications of these differences on routine QA
3. Become familiar with tools provided by the manufacturer to facilitate GK QA
4. Understand the difficulties associated with dosimetriccalibration of GSR units
5. Review the use of radiochromic film for GK QA
TU‐E‐213A‐02: Implementing New Technologies for Stereotactic Radiosurgery and Stereotactic Body Radiation Therapy36(2009); http://dx.doi.org/10.1118/1.3182437View Description Hide Description
Stereotactic radiosurgery has become the standard of care in the treatment of many cranial neoplasms. This success has stimulated significant interest in the application of such an approach for the treatment of extracranial tumors. The development of image guidance techniques has rapidly facilitated adoption of Stereotactic Body Radiation therapy(SBRT) in a number of anatomical sites. Both SRS and SRT pose a number of practical challenges in acceptance testing, commissioning and clinical implementation. These include: uncertainties in small field measurement and dose calculation, appropriate use of phantoms for verifying image fusion and assuring end‐to‐end localization accuracy, implementing effective immobilization techniques, understanding and adapting for intrafraction motion, planning and delivery for fixed beam and rotational irradiation, and maintaining appropriate QA procedures. In this presentation we will review these challenges with respect to linac‐based SRS and SBRT.
36(2009); http://dx.doi.org/10.1118/1.3182438View Description Hide Description
The CyberKnife (Accuray, Inc. Sunnyvale, CA) is a stereotactic radiotherapy unit, designed to treat both intracranial and extracranial targets with sub‐millimeter spatial accuracy. An industrial robot has a compact 6 MV x‐band linac as its payload. The robot is able to orient the linac with six degrees of freedom, and to aim its x‐ray beam at the target volume in a non‐isocentric and non‐coplanar fashion. Typically, hundreds of beams (selected from thousands of possible beam angles) are delivered during each treatment fraction. A bi‐plane digital radiography system determines and feeds‐back target position coordinates to the robot throughout treatment, allowing the robot to continuously correct its aim to account for intra‐fraction patient and target movement. The CyberKnife uses several different tracking methodologies depending upon the type of target being treated. Both rigid body and deformable body geometries are employed. Special correlative tracking techniques have been developed to track targets that move with respiration. With nearly real‐time correction for target motion and highly precise dose delivery, the CyberKnife allows the practitioner to employ tighter margins and to deliver high doses per fraction accurately.
This talk is intended to review the unique features of the CyberKnife system, and to discuss how those features require special considerations in site planning, acceptance testing, commissioning, quality assurance,treatment planning, and clinical implementation. Examples of common clinical applications and dose regimens will also be presented.
1. Understand the fundamental design and functionality of the CyberKnife system.
2. Understand the impact of machine design on site planning, acceptance testing, commissioning, treatment planning, as well as system and sub‐system quality assurance.
3. Understand the different clinical considerations associated with roboticSRS and SBRT.
4. Enable the attendee to introduce a CyberKnife system into his/her clinical practice efficiently, effectively, and safely.
- ACR Accreditation for MRI ‐ Role of the Medical Physicist
36(2009); http://dx.doi.org/10.1118/1.3182502View Description Hide Description
The medical physicist plays an important role in several aspects of the ACR MRI accreditation program. In 2008 significant program changes were made. The new program is modular so that facilities can apply for accreditation in any or all of six clinical modules depending on the practice. Each of the modules allows flexible protocol choices for clinical image submission, while setting minimum requirements for spatial resolution, temporal resolution, and total scan time. Two phantoms are now available to allow accreditation of both large bore magnets and small bore orthopedic MRI systems.
During the application or renewal process the physicist can provide expertise to MRI facilities by acquiring the phantom images and assessing whether phantom image quality will meet ACR requirements. When image quality measures fall below standards, the physicist can identify the cause and offer recommendations for corrective action. In addition, prior to acquiring clinical images for accreditation, the physicist can determine whether the site's clinical protocols provide adequate spatial and temporal resolution.
1. Present an overview of the new modular ACR MRI Accreditation program as it applies to phantom image acquisition for accreditation application.
2. Discuss phantom image quality failures, possible causes and potential remedies.
3. Provide advice for avoiding common pitfalls in the phantom image submission process.
36(2009); http://dx.doi.org/10.1118/1.3182503View Description Hide Description
In recent years, the American College of Radiology (ACR) Magnetic Resonance Accreditation Program (MRAP) has been adopted by over 4600 sites, nearly half of the estimated MRI facilities in the United States. Those sites agree to follow a weekly QC program set up and monitored by a qualified medical physicist or MR scientist.
This lecture will overview the QC requirements for high and low field MRI units from multiple vendors. Each unit has different terminology for center frequency and transmitter gain and different methods of locating them. These need to be known by the medical physicist and shown to the technologist. Suggestions will be given for teaching the QC to technologists. Suggestions will be given for establishing baselines and monitoring the QC program. Examples will be shown of evaluations of both properly functioning MRI scanners and poorly functioning units.
1. Learn the technologist QC requirements for the ACR MR accreditation program and the physicist / MR scientist's role in setting up the program.
2. Learn how to locate the applicable QC parameters on different MRI systems.
3. Learn how to establish MR QC baselines and evaluate the technologist QC program.
36(2009); http://dx.doi.org/10.1118/1.3182504View Description Hide Description
The ACR MRI Accreditation program requires that sites applying for MRI accreditation submit an annual MRI system performance evaluation performed by a medical physicist or MR scientist. The medical physicist/MR Scientist follows the ACR MRIQuality Control (QC) Manual in order to perform a complete annual system performance evaluation. This evaluation includes an evaluation of the weekly QC performed by a technologist.
This presentation shall review a standard set of tests and procedures that satisfy the ACR compliance testing guidelines. A model program for satisfying the ACR MRI performance standards shall be provided. Steps for setting up the QC Program include determining which tests are appropriate, establishing a mutually agreeable testing frequency, training technologist and other personnel to carry out their portions of the MRI QC program, reviewing artifacts and other problems that result from the test data and documenting corrective actions that are taken. Attention will be paid to specific tests, such as Magnetic Field Homogeneity, in which spectral width, phase‐difference and bandwidth difference methods will be discussed and compared. Tests for gradient field linearity (geometric distortion) and radio frequency (RF) coil testing will be presented, including measuring slice thickness accuracy, determining mean and maximum signal‐to‐noise ratios, ghosting ratios and image intensity uniformity. The relevance, applicability, and performance of each element will be discussed.
A brief discussion of suggested, additional elements that would constitute an Acceptance Testing (AT) program for Magnetic Resonance Imagingdevices will conclude the presentation. Tasks under consideration will include comparing equipment received with purchase order specifications, checking environmental conditions of the MRI suite, RF room shielding survey, cryogen consumption, magnetic field stability, magnetic fringe field survey, gradient field strength, eddy current evaluation, evaluation of image acquisition and image processing software and optional features. Individual testing procedures and the rationale for their use will be presented and performance evaluation acceptance criteria will be suggested.
Upon completion of this presentation, participants will understand how to:
• Design Quality Control (QC) Testing and Acceptance Testing (AT) programs for Magnetic Resonance Imaging
• Define the role of the Technologist, equipment service personnel and the clinical medical physicist/MR scientist in this programs.
• Configure the equipment necessary for MRI QC and AT testing.
- Setting up a Stereotactic Body Radiation Therapy (SBRT) Program in the Clinic
WE‐D‐213A‐01: Establishing a Stereotactic Body Radiation Therapy (SBRT) Clinical Program, Part 1: Physics and Dosimetry36(2009); http://dx.doi.org/10.1118/1.3182550View Description Hide Description
Stereotactic body radiation therapy(SBRT) is a technique in which dose is delivered using either in a single fraction or a hypo‐fractionated schedule. The technique is characterized by the use of high doses per fraction, increased spatial accuracy of the radiationdelivery, and a rapid fall‐off of dose outside the treatment volume. The overall goal is to minimize the direct effects of radiation on the surrounding normal tissue while delivering a dose biologically equivalent (or greater) to several weeks of conventionally fractionated radiation therapy to the treatment volume. The intent of SBRTtreatment has been to deliver noninvasive tumor‐ablative doses to sharply demarcated lesions so that clinical outcomes comparable to surgery could be achieved without surgical complications. The majority of published clinical data describes the treatment of lung,liver and spinal tumors. The radiobiology of short‐course, high‐dose‐per‐fraction regimens suggests that utilizing SBRT, with significant local dose escalation even to curative doses, is feasible. The number of fractions and total doses currently in clinical use varies widely in the literature, typically ranging from 60 Gy delivered in 10 fractions to 30 Gy delivered in a single fraction.
The Physics and Dosimetry section of the session is to advise medical physicists establishing such a program. The presentation will include an overview of the AAPM Task Group No. 101 on recommendations for SBRT, which has been charged with (1) review the literature and identify the range of historical experiences, reported clinical findings and expected outcomes, (2) review the relevant commercial products and associated clinical findings for an assessment of system capabilities and technology limitations, (3) determine required criteria for setting‐up and establishing an SBRT facility, including protocols, equipment, resources, and QA procedures, and (4) to develop consistent documentation for prescribing, reporting, and recording SBRTtreatmentdelivery.
1. Present the recommended guidelines on establishing an SBRT clinic as presented in the current version of the AAPM Task Group No. 101.
2. Present the technical issues for clinical implementation of SBRT equipment, space considerations, time and personnel considerations.
3. Review the commercial products commonly employed for SBRT with regard to image guidance, localization devices, patient alignment and verification systems
4. Understand the limitation of some treatment planning systems and dose calculation alogorithms as they apply to the highly heterogenous doses within a small target volume typically planned for SBRT.
5. Review the overall quality assurance procedures for systems and patient specific parameters for SBRTdeliveries.
WE‐D‐213A‐02: Establishing a Stereotactic Body Radiation Therapy (SBRT) Clinical Program, Part 2: Clinical and Radiobiological Considerations36(2009); http://dx.doi.org/10.1118/1.3182551View Description Hide Description
Stereotactic Body Radiation Therapy(SBRT) has emerged as an important form of cancer therapy with broad application across a spectrum of tumor types in the primary and metastatic settings. The capability of safely administering a very high dose of therapeuticradiation to discrete extracranial tumor sites has raised new questions about the radiobiology of high dose per fraction treatment. Accumulating clinical experiences are yielding new insights into practical aspects of tumor and normal tissue responses to high dose per fraction treatment.
The current practice of SBRT has evolved to some extent from knowledge gained from principles learned from the practice of cranial stereotactic radiosurgery(SRS). For the integration of SBRT into clinical practice, medical physicists and radiationoncologists are advised to collaborate closely to establish clear guidelines for normal tissuedose constraints and tumordose prescription practices that are suitable to their own clinical environment. Published literature relevant to this objective will be discussed. A consistent strategy for contouring sensitive organs is encouraged. The technological challenges introduced by the high dose and high precision paradigm of SBRT are presented and the vital relationship between physicist and physician in this context cannot be overemphasized.
The radiobiological issues that have been parsed by this new paradigm of treatment will be explored, including understanding of conventional, hypofractionated and single dosetreatments, radiobiological modeling, and the concepts of equivalent doses. Future trends in SBRT will be discussed. Clinical outcomes after SBRT in a variety of setting will be summarized.
1. Review and understand the major issues related to the use SBRT for, including key strategies for uniform contouring and determination of organ tolerances.
2. Review and understand the common clinically observed normal tissue responses to SBRT and the inferences to be drawn regarding the practical radiobiology of high dose per fraction therapy
3. Discuss these new paradigms of fractionation as they relate to conventional regimes, including hypofractionation and single dosetreatments and their radiobiological threshold effects.
4. Review potential future application of SBRT
- Practical Application of Beam Calibration Protocols
36(2009); http://dx.doi.org/10.1118/1.3182581View Description Hide Description
Purpose: Since its publication in September, 1999 (Medical Physics 26(9), pp 1847–90), the TG‐51 calibration protocol has been implemented in most US institutions. This presentation, one part of a workshop session on practical aspects of treatment unit calibrations, will review the basics of TG‐51 calibrations for conventional linear accelerator beams. Methods and Materials: Using the TG‐51 publication as a guide, practical aspects of performing a TG‐51 calibration of a treatment unit will be described. Relevant definitions of the key parameters to be acquired, either through measurement or calculation, will be reviewed. Starting from the acquisition of valid absorbed‐dose to water calibration factor, methods for determining each of the parameters used in the TG‐51 calculation will be reviewed. Common techniques will be illustrated and some common mistakes will be discussed. Publicly available resources will be described. Methods for verifying the results of calibrations, particularly when spreadsheets or other calculations aids are utilized, will also be discussed.
1. Review the basic implementation of TG‐51 for conventional external beam measurements.
2. Discuss practical aspects of the selection of ion chamber,electrometer and measurement conditions for TG‐51 calibrations.
3. Demonstrate some techniques for determining TG‐51 parameters such as Pion, Ppol, and kQ
4. Discuss some common mistakes and how to avoid them.
36(2009); http://dx.doi.org/10.1118/1.3182582View Description Hide Description
Small field dosimetry for Cyberknife is the most challenging aspects of machine commissioning and annual QA. Accurate reference dosimetry, relative output factors, TPR and OCR data form the baseline for accurate dose delivery. This presentation will give practical guidance on ways to achieve an accurate dosimetricmeasurement in a time‐efficient way.
First, a new reference dosimetry concept based on a recent publication by the IAEA Working group on “Small Field Dosimetry” will be introduced. This new concept explains how to approach reference dosimetry for radiation therapy machines which do not have a 10 cm × 10 cm field as required by TG51 or IAEA Report 398. Using an example, it will be explained how to calculate kQ for the 60 mm collimator. Suitable detectors for the reference dosimetry with the 60 mm collimator will be discussed. This will include a review of the measureddose dependency on chamber length for the non‐flattened field of Cyberknife based on recently published literature. A discussion on reference dosimetry for the IRIS collimator will conclude reference dosimetry.
Second, relative output factor measurements, focusing on collimators ⩽ 10 mm, will be introduced. The importance of checking the detector for correct inverse‐square law will be shown with a clinical example. Suitable detectors for output measurements are different from detectors used for reference dosimetry. Special consideration will be given to IRIS collimator output factors and their dependency on the accuracy of the mechanical field size tolerance.
This presentation will end with a section on measurements of the TPR and OCR data. Especially measuring OCR data for the IRIS collimator, which require 15 degree and 105 degree scans in addition to the in‐plane and cross‐plane scans, will be discussed. Data processing as well as tips & tricks to streamline the process will be given. Quality assurance and secondary dose verification processes as applicable to the dosimetry will be covered.
1. Understanding the new IAEA “Small Field Dosimetry” Paradigm on reference fielddosimetry.
2. Understanding which detector types are suitable for Cyberknife small field dosimetry, and why.
3. Understanding Cyberknife‐specific challenges.
36(2009); http://dx.doi.org/10.1118/1.3182583View Description Hide Description
Despite the emphasis on megavoltage radiation therapy, kV units are still being acquired and used in clinical radiation therapy for superficial lesions and specialized treatment techniques. The dosimetry of kV X‐ray beams is tricky and subject to increased uncertainties due to the energy dependence of many quantities involved in determination of absorbed dose at the reference point. In addition, there are a large variety of beam modifiers and applicators used each of which requires separate relative output measurements sometimes affected by issues such as electron contamination and scatter. This presentation concentrates on the practical aspects of a typical clinical AAPM TG61 protocol implementation. Following aspects will be discussed: (1) a review of the calibration protocol formalism; (2) ionization chamber types and calibration; (3) beam quality measurements; (4) relative measurements for open and closed applicators; (5) other clinical aspects such as tertiary collimation, etc.
1. understanding of the concepts and formalism of the TG61 protocol
2. understanding the characteristics of ionization chambers with respect to kV dosimetry
3. elucidating aspects of the commissioning of orthovoltage units
4. illustrating special clinical situations
36(2009); http://dx.doi.org/10.1118/1.3182584View Description Hide Description
Electron beamdosimetry can be a deceptively simple endeavor. On one hand, the process of measuring and using unrestricted electron cone factors is remarkably straight forward. However, making measurements in restricted fields especially at extended treatment distances can prove to be quite a challenge, especially if the field is extremely narrow. Ionization chamber correction coefficients for cylindrical and plane‐parallel chambers can depend on many factors and ensuring that the correct factors are applied for measurements at depth in water or solid phantoms can be confusing.
This talk will cover proper measurement set up and technique, problems and pitfalls associated with detector selection for various electron measurement situations, chamber response characteristics that should be known and determined before use for electron dosimetry, and efficient techniques for performing routine commissioning measurements and special dosimetry for electron beams. The influence of TG‐51 calibration protocol on routine clinical measurements will also be covered along with some clinical techniques where electron beam measurements are particularly challenging and interesting.
1. Ionization chamber response characteristics in electron beams
2. Selection of detectors for measurements in electron beams
3. Use of ionization chambers and other detectors in electron beams measurements
4. Special measurement situations: restricted field measurements, measurements at extended distances, measurements in non‐water phantoms
5. Clinical situations involving special electron beam measurements