Biological effects of the Auger emitter iodine-125: a review. Report No. 1 of AAPM Nuclear Medicine Task Group No. 6.

The biological implications of Auger electron cascades following inner shell ionization of atoms have been of interest for over 25 years. By virtue of their decay via orbital electron capture and/or internal conversion, several biomedical radionuclides emit numerous low-energy electrons spontaneously. The biological effects of such radionuclides incorporated into tissues cannot be predicted a priori because of the highly localized patterns of energy deposition by the electrons. Results of extensive research using Iodine-125 as a model Auger electron emitter are now available. This article presents an up-to-date review of the physical and radiobiological data on this Auger emitter. Valuable concepts concerning the action of internal Auger emitters are identified phenomenologically, and questions that need to be answered are indicated. The present understanding provides a scientific basis toward estimation of risk associated with Auger emitters used in diagnosis, and suggests potential applications to therapy.     

Intraoperative radiation therapy using mobile electron linear accelerators: report of AAPM Radiation Therapy Committee Task Group No. 72

Intraoperative radiation therapy (IORT) has been customarily performed either in a shielded operating suite located in the operating room (OR) or in a shielded treatment room located within the Department of Radiation Oncology. In both cases, this cancer treatment modality uses stationary linear accelerators. With the development of new technology, mobile linear accelerators have recently become available for IORT. Mobility offers flexibility in treatment location and is leading to a renewed interest in IORT. These mobile accelerator units, which can be transported any day of use to almost any location within a hospital setting, are assembled in a nondedicated environment and used to deliver IORT. Numerous aspects of the design of these new units differ from that of conventional linear accelerators. The scope of this Task Group (TG-72) will focus on items that particularly apply to mobile IORT electron systems. More specifically, the charges to this Task Group are to (i) identify the key differences between stationary and mobile electron linear accelerators used for IORT, (ii) describe and recommend the implementation of an IORT program within the OR environment, (iii) present and discuss radiation protection issues and consequences of working within a nondedicated radiotherapy environment, (iv) describe and recommend the acceptance and machine commissioning of items that are specific to mobile electron linear accelerators, and (v) design and recommend an efficient quality assurance program for mobile systems.     

Quality assurance for computed-tomography simulators and the computed-tomography-simulation process: report of the AAPM Radiation Therapy Committee Task Group No. 66

This document presents recommendations of the American Association of Physicists in Medicine (AAPM) for quality assurance of computed-tomography- (CT) simulators and CT-simulation process. This report was prepared by Task Group No. 66 of the AAPM Radiation Therapy Committee. It was approved by the Radiation Therapy Committee and by the AAPM Science Council.     

Recommendations on performance characteristics of diagnostic exposure meters: report of AAPM Diagnostic X-Ray Imaging Task Group No. 6.

Task Group 6 of the Diagnostic X-Ray Imaging Committee of the American Association of Physicists in Medicine (AAPM) was appointed to develop performance standards for diagnostic x-ray exposure meters. The recommendations as approved by the Diagnostic X-Ray Imaging Committee and the Science Council of the AAPM are delineated in this report and provide specifications on meter precision, calibration accuracy, calibration reference points, linearity, energy dependence, exposure rate dependence, leakage, amplification gain settings, directional dependence, the stem effect, constancy checks, and calibration intervals. The report summarizes recommendations for meters used in mammography, general purpose radiography including special procedures, computed tomography, and radiation safety surveys for x-ray radiography.     

Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations

Since publication of the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report in 1995 (TG-43), both the utilization of permanent source implantation and the number of low-energy interstitial brachytherapy source models commercially available have dramatically increased. In addition, the National Institute of Standards and Technology has introduced a new primary standard of air-kerma strength, and the brachytherapy dosimetry literature has grown substantially, documenting both improved dosimetry methodologies and dosimetric characterization of particular source models. In response to these advances, the AAPM Low-energy Interstitial Brachytherapy Dosimetry subcommittee (LIBD) herein presents an update of the TG-43 protocol for calculation of dose-rate distributions around photon-emitting brachytherapy sources. The updated protocol (TG-43U1) includes (a) a revised definition of air-kerma strength; (b) elimination of apparent activity for specification of source strength; (c) elimination of the anisotropy constant in favor of the distance-dependent one-dimensional anisotropy function; (d) guidance on extrapolating tabulated TG-43 parameters to longer and shorter distances; and (e) correction for minor inconsistencies and omissions in the original protocol and its implementation. Among the corrections are consistent guidelines for use of point- and line-source geometry functions. In addition, this report recommends a unified approach to comparing reference dose distributions derived from different investigators to develop a single critically evaluated consensus dataset as well as guidelines for performing and describing future theoretical and experimental single-source dosimetry studies. Finally, the report includes consensus datasets, in the form of dose-rate constants, radial dose functions, and one-dimensional (1D) and two-dimensional (2D) anisotropy functions, for all low-energy brachytherapy source models that met the AAPM dosimetric prerequisites [Med. Phys. 25, 2269 (1998)] as of July 15, 2001. These include the following 125I sources: Amersham Health models 6702 and 6711, Best Medical model 2301, North American Scientific Inc. (NASI) model MED3631-A/M, Bebig/Theragenics model I25.S06, and the Imagyn Medical Technologies Inc. isostar model IS-12501. The 103Pd sources included are the Theragenics Corporation model 200 and NASI model MED3633. The AAPM recommends that the revised dose-calculation protocol and revised source-specific dose-rate distributions be adopted by all end users for clinical treatment planning of low energy brachytherapy interstitial sources. Depending upon the dose-calculation protocol and parameters currently used by individual physicists, adoption of this protocol may result in changes to patient dose calculations. These changes should be carefully evaluated and reviewed with the radiation oncologist preceding implementation of the current protocol.     

Intravascular brachytherapy physics: report of the AAPM Radiation Therapy Committee Task Group no. 60. American Association of Physicists in Medicine

Recent preclinical and clinical studies indicate that irradiation using ionizing radiation in the dose range of 15 to 30 Gy may reduce the occurrence of restenosis in patients who have undergone an angioplasty. Several delivery systems of intravascular brachytherapy have been developed to deliver radiation doses in this range with minimal normal tissue toxicity. In late 1995 the American Association of Physicists in Medicine (AAPM) formed a task group to investigate these issues and to report the current state of the art of intravascular brachytherapy physics. The report of this task group is presented here.     

A dosimetric uncertainty analysis for photon-emitting brachytherapy sources: report of AAPM Task Group No. 138 and GEC-ESTRO

This report addresses uncertainties pertaining to brachytherapy single-source dosimetry preceding clinical use. The International Organization for Standardization (ISO) Guide to the Expression of Uncertainty in Measurement (GUM) and the National Institute of Standards and Technology (NIST) Technical Note 1297 are taken as reference standards for uncertainty formalism. Uncertainties in using detectors to measure or utilizing Monte Carlo methods to estimate brachytherapy dose distributions are provided with discussion of the components intrinsic to the overall dosimetric assessment. Uncertainties provided are based on published observations and cited when available. The uncertainty propagation from the primary calibration standard through transfer to the clinic for air-kerma strength is covered first. Uncertainties in each of the brachytherapy dosimetry parameters of the TG-43 formalism are then explored, ending with transfer to the clinic and recommended approaches. Dosimetric uncertainties during treatment delivery are considered briefly but are not included in the detailed analysis. For low- and high-energy brachytherapy sources of low dose rate and high dose rate, a combined dosimetric uncertainty <5% (k=1) is estimated, which is consistent with prior literature estimates. Recommendations are provided for clinical medical physicists, dosimetry investigators, and source and treatment planning system manufacturers. These recommendations include the use of the GUM and NIST reports, a requirement of constancy of manufacturer source design, dosimetry investigator guidelines, provision of the lowest uncertainty for patient treatment dosimetry, and the establishment of an action level based on dosimetric uncertainty. These recommendations reflect the guidance of the American Association of Physicists in Medicine (AAPM) and the Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) for their members and may also be used as guidance to manufacturers and regulatory agencies in developing good manufacturing practices for sources used in routine clinical treatments.     

Clinical use of electronic portal imaging: report of AAPM Radiation Therapy Committee Task Group 58

AAPM Task Group 58 was created to provide materials to help the medical physicist and colleagues succeed in the clinical implementation of electronic portal imaging devices (EPIDs) in radiation oncology. This complex technology has matured over the past decade and is capable of being integrated into routine practice. However, the difficulties encountered during the specification, installation, and implementation process can be overwhelming. TG58 was charged with providing sufficient information to allow the users to overcome these difficulties and put EPIDs into routine clinical practice. In answering the charge, this report provides; comprehensive information about the physics and technology of currently available EPID systems; a detailed discussion of the steps required for successful clinical implementation, based on accumulated experience; a review of software tools available and clinical use protocols to enhance EPID utilization; and specific quality assurance requirements for initial and continuing clinical use of the systems. Specific recommendations are summarized to assist the reader with successful implementation and continuing use of an EPID.     

QA for helical tomotherapy: report of the AAPM Task Group 148

Helical tomotherapy is a relatively new modality with integrated treatment planning and delivery hardware for radiation therapy treatments. In view of the uniqueness of the hardware design of the helical tomotherapy unit and its implications in routine quality assurance, the Therapy Physics Committee of the American Association of Physicists in Medicine commissioned Task Group 148 to review this modality and make recommendations for quality assurance related methodologies. The specific objectives of this Task Group are: (a) To discuss quality assurance techniques, frequencies, and tolerances and (b) discuss dosimetric verification techniques applicable to this unit. This report summarizes the findings of the Task Group and aims to provide the practicing clinical medical physicist with the insight into the technology that is necessary to establish an independent and comprehensive quality assurance program for a helical tomotherapy unit. The emphasis of the report is to describe the rationale for the proposed QA program and to provide example tests that can be performed, drawing from the collective experience of the task group members and the published literature. It is expected that as technology continues to evolve, so will the test procedures that may be used in the future to perform comprehensive quality assurance for helical tomotherapy units.     

Stereotactic body radiation therapy: the report of AAPM Task Group 101

Task Group 101 of the AAPM has prepared this report for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for the external-beam radiation therapy technique referred to as stereotactic body radiation therapy (SBRT). The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information is provided for establishing a SBRT program, including protocols, equipment, resources, and QA procedures. Additionally, suggestions for developing consistent documentation for prescribing, reporting, and recording SBRT treatment delivery is provided.     

Supplement to the 2004 update of the AAPM Task Group No. 43 Report

Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43U1), several new low-energy photon-emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical use as of January 10, 2005, and are posted on the Joint AAPM/RPC Brachytherapy Seed Registry. Consequently, the AAPM has prepared this supplement to the 2004 AAPM TG-43 update. This paper presents the AAPM-approved consensus datasets for these sources, and includes the following 125I sources: Amersham model 6733, Draximage model LS-1, Implant Sciences model 3500, IBt model 1251L, IsoAid model IAI-125A, Mentor model SL-125/ SH-125, and SourceTech Medical model STM1251. The Best Medical model 2335 103Pd source is also included. While the methodology used to determine these data sets is identical to that published in the AAPM TG-43U1 report, additional information and discussion are presented here on some questions that arose since the publication of the TG-43U1 report. Specifically, details of interpolation and extrapolation methods are described further, new methodologies are recommended, and example calculations are provided. Despite these changes, additions, and clarifications, the overall methodology, the procedures for developing consensus data sets, and the dose calculation formalism largely remain the same as in the TG-43U1 report. Thus, the AAPM recommends that the consensus data sets and resultant source-specific dose-rate distributions included in this supplement be adopted by all end users for clinical treatment planning of low-energy photon-emitting brachytherapy sources. Adoption of these recommendations may result in changes to patient dose calculations, and these changes should be carefully evaluated and reviewed with the radiation oncologist prior to implementation of the current protocol.     

Verification of monitor unit calculations for non-IMRT clinical radiotherapy: report of AAPM Task Group 114

The requirement of an independent verification of the monitor units (MU) or time calculated to deliver the prescribed dose to a patient has been a mainstay of radiation oncology quality assurance. The need for and value of such a verification was obvious when calculations were performed by hand using look-up tables, and the verification was achieved by a second person independently repeating the calculation. However, in a modern clinic using CT/MR/PET simulation, computerized 3D treatment planning, heterogeneity corrections, and complex calculation algorithms such as convolution/superposition and Monte Carlo, the purpose of and methodology for the MU verification have come into question. In addition, since the verification is often performed using a simpler geometrical model and calculation algorithm than the primary calculation, exact or almost exact agreement between the two can no longer be expected. Guidelines are needed to help the physicist set clinically reasonable action levels for agreement. This report addresses the following charges of the task group: (1) To re-evaluate the purpose and methods of the "independent second check" for monitor unit calculations for non-IMRT radiation treatment in light of the complexities of modern-day treatment planning. (2) To present recommendations on how to perform verification of monitor unit calculations in a modern clinic. (3) To provide recommendations on establishing action levels for agreement between primary calculations and verification, and to provide guidance in addressing discrepancies outside the action levels. These recommendations are to be used as guidelines only and shall not be interpreted as requirements.     

Quality assurance of U.S.-guided external beam radiotherapy for prostate cancer: report of AAPM Task Group 154

Task Group 154 (TG154) of the American Association of Physicists in Medicine (AAPM) was created to produce a guidance document for clinical medical physicists describing recommended quality assurance (QA) procedures for ultrasound (U.S.)-guided external beam radiotherapy localization. This report describes the relevant literature, state of the art, and briefly summarizes U.S. imaging physics. Simulation, treatment planning and treatment delivery considerations are presented in order to improve consistency and accuracy. User training is emphasized in the report and recommendations regarding peer review are included. A set of thorough, yet practical, QA procedures, frequencies, and tolerances are recommended. These encompass recommendations to ensure both spatial accuracy and image quality.     

Functional fitting of interstitial brachytherapy dosimetry data recommended by the AAPM Radiation Therapy Committee Task Group 43. American Association of Physicists in Medicine

This work was undertaken to expedite implementation of the AAPM Task Group 43 recommendations, which call for significant modifications in the way dose is calculated for interstitial sources of 192Ir, 125I, and 103Pd as well as significant changes in the dose rate constant for 125I sources. The TG43 recommendations include a new formalism for dose calculation at points defined by the radial distance, r, from the source center and the angle, theta, that such a radius makes with the source axis. For each source type, values are tabulated for the radial dose function, the anisotropy function, and the anisotropy factor. The TG43 report includes fitting functions for the radial dose function in the form of polynomials, which are poorly behaved outside the range of fitted data. No functions are offered for the anisotropy function data or the anisotropy factor data, both of which could profit from some smoothing by such functions. We have found a double exponential fit to the radial dose function that not only approximates the data adequately but also appropriately approaches zero for very large distances. The anisotropy function is conveniently fit with a form of type 1 - f(r,theta)cos(theta)e(cr), which is exactly 1 at theta=90 degrees and approaches 1 for large r (for c<0), where f(r,theta) is a selected polynomial in the two variables. The form chosen for the anisotropy factor was 1 - (a+br)e(cr), which appropriately approaches 1 for large r (and c<0). Functional fits of these types are expected to facilitate implementation of TG43 recommendations, in that they may be either incorporated into dose algorithms or used to generate lookup tables of either the x, y or the r, theta format.     

The management of respiratory motion in radiation oncology report of AAPM Task Group 76

This document is the report of a task group of the AAPM and has been prepared primarily to advise medical physicists involved in the external-beam radiation therapy of patients with thoracic, abdominal, and pelvic tumors affected by respiratory motion. This report describes the magnitude of respiratory motion, discusses radiotherapy specific problems caused by respiratory motion, explains techniques that explicitly manage respiratory motion during radiotherapy and gives recommendations in the application of these techniques for patient care, including quality assurance (QA) guidelines for these devices and their use with conformal and intensity modulated radiotherapy. The technologies covered by this report are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques. The main outcome of this report is a clinical process guide for managing respiratory motion. Included in this guide is the recommendation that tumor motion should be measured (when possible) for each patient for whom respiratory motion is a concern. If target motion is greater than 5 mm, a method of respiratory motion management is available, and if the patient can tolerate the procedure, respiratory motion management technology is appropriate. Respiratory motion management is also appropriate when the procedure will increase normal tissue sparing. Respiratory motion management involves further resources, education and the development of and adherence to QA procedures.     

Refinements to the geometry factor used in the AAPM Task Group Report No. 43 necessary for brachytherapy dosimetry calculations. American Association of Physicists in Medicine

Determination of the geometry factor is necessary for brachytherapy dosimetry calculations as recommended by the AAPM Task Group No. 43 (TG-43). The equivalence and errors associated with use of a point source approximation for an extended line segment source are examined. For all angles, the error using the point source approximation is less than 2% for distances in which the ratio of radius to active source length, (r/L), exceed about 3.6. A novel approach to determining the geometry factor using Monte Carlo methods is discussed in which the particle flux emanates from the active source and streams with no interactions occurring within the source or phantom. This method was performed for determining the geometry factor along the transverse axis for six brachytherapy sources. Differences in the geometry factor exceeding 2% between the point source approximation and that obtained using Monte Carlo methods occurred at distances ranging from 0.5 to 5 mm from the source center along the transverse plane. The merits of the Monte Carlo approach for solving the geometry factor are discussed in light of using a point or line source approximation for calculating additional brachytherapy dosimetry parameters.