Index of content:
Volume 35, Issue 6, June 2008
- Therapy: Continuing Education Course: Auditorium C
- CE ‐ Therapy: Deformable Image Registration: Methods and Clinical Endpoints
35(2008); http://dx.doi.org/10.1118/1.2962424View Description Hide Description
Acquisition of anatomic and functional data from magnetic resonance imaging and nuclear medicine studies is becoming increasingly common for patient management in radiation therapy. These data can help improve tumor localization and normal tissue delineation for treatment planning and may provide information about treatment efficacy during or after a course of radiotherapy. Time series data from serial and 4D CT before and during the treatment course, including CT data acquired in the treatment room at the time of treatment, is also helping to estimate motion and shape changes of relevant anatomy. In order to fully realize the benefits of these data, the different imaging studies must be registered to each other or to a common coordinate system. The geometric transformation required to register the different image data can range from simple rotate‐translate to account for differences in patient orientation to 3D or 4D deformation models to account for changes in internal anatomy during and over the course of therapy. Once registered, data derived from the various studies such as anatomic outlines and computed dose can be integrated or fused to help construct a more complete and accurate representation of the patient.
This lecture will focus on the mechanics of registering and displaying data from different imaging studies using distinct modalities or a single modality over time. A taxonomy of the different methods will be described. Methods for display and interaction with multimodality data will also be presented. The overall goal is to provide the basic knowledge required to understand what is happening “under‐the‐hood” of the different registration systems one might encounter in the clinic, the different ways these systems are being used for patient management and their limitations.
1. Understand the basic mechanics of deformable image registration and data fusion techniques.
2. Understand the tools used to combine, display & interact with multimodality/4D image and dose data.
3. Understand the clinical use and limitations of these techniques for Tx planning, Tx delivery and plan adaptation.
- CE‐Therapy: Clinical Implementation on Respiration Motion Correlated Imaging, Treatment Planning and Delivery
MO‐A‐AUD C‐01: Practical Considerations for Respiratory Colarated CT Imaging and Target Volume Delineation35(2008); http://dx.doi.org/10.1118/1.2962322View Description Hide Description
Accurate and conformal treatment of tumors in abdomen and thorax is challenging due to respiratory related motion. Respiratory corralled CTimaging combined with gated treatment delivery can improve both accuracy and conformality of delivered dose distributions. Implementation of respiratory correlated imaging and treatment delivery can be performed in multiple ways and understanding of different techniques and technical challenges is critical for efficient and safe clinical implementation. Formal recommendations for commissioning and clinical use of this technology is scarce. Inadequate evaluation and understanding of these systems can lead to significant treatment errors. This presentation deals with practical issues of respiratory correlated CTimaging and commissioning. Examples of some commonly seen image artifacts are also discussed. Furthermore, contouring based on respiratory correlated images is discussed, again with examples of some of potential pitfalls and artifacts.
1. Commissioning process for respiratory correlated CTimaging and delivery techniques.
2. Use of respiratory correlated images for target delineation.
3. Common image artifacts and contouring errors seen with respiratory correlated imaging.
MO‐A‐AUD C‐02: Clinical Implementation of Respiration Motion Correlated Imaging, Treatment Planning and Delivery35(2008); http://dx.doi.org/10.1118/1.2962323View Description Hide Description
Respiratory motion is a significant factor in determining a suitable planning target volume (PTV) that surrounds the demonstrable gross tumor volume (GTV) in the radiotherapy of mobile lesions. The advent of respiratory phase correlation (4D) and multi‐slice CT technology has enabled patient‐specific determination of both demonstrable tumor volume and its motion from a single acquisition. Management of such additional information during treatment planning and delivery however presents several challenges. Furthermore, guidelines for establishing clinical treatment planning and delivery protocols based on respiratory correlated imaging data differ from one institution to the other. The purpose of this presentation is to educate the community on the different respiratory correlated radiotherapy approaches currently available and compare the benefits and pitfalls in each case. Special focus will be on treatment planning,dose calculation and treatment delivery related issues.
1. Understand the different respiratory correlated treatment planning and delivery approaches.
2. Compare the benefits and pitfalls of each of the above approaches.
3. Develop and establish respiratory correlated imaging,treatment planning and delivery appropriate to the available equipment.
- CE‐Therapy: Dose Calculation Algorithms in 3DCRT and IMRT
35(2008); http://dx.doi.org/10.1118/1.2962678View Description Hide Description
The majority of photon dose calculation approaches today are model based dose calculation algorithms, in which the dose distribution is predicted from first principles. At the basic level there are the pencil beam convolution models, with further sophistication introduced by the collapsed cone convolution models. While the basic element of both is a convolution, which is performed between the energy released in each voxel and a dose spread kernel, different approximations have been introduced to deal with limitations in computer speed and incomplete physics. As it is important that the clinical physicist understands the limitations of these dose calculation approaches, this teaching lecture aims to describe these models and discuss the advantages and disadvantages of them. When possible, the individual implementation of the algorithms in commercial treatment planning systems will be discussed.
The models covered firstly include pencil beam models, which are still the basis for most dose calculations in 3DCRT and IMRT optimizations today. Secondly, more recent pencil beam implementation that include modelling of changes in electron transport, particularly in the lateral direction, will be discussed. Finally the highly accurate collapsed cone models will be covered. Some comparisons with Monte Carlo generated data will be presented to highlight the limitations of the algorithms in focus.
1. To provide an educational review of the physics and techniques behind convolution algorithms.
2. To review the methods used to improve the simulation efficiency i.e. pencil beam and collapsed cone convolutions.
3. To briefly review the vendor codes currently used for clinical treatment planning.
4. To discuss the issues associated with experimental verification of dose calculation algorithms.
5. To briefly review the potential clinical implications of accurate calculated dose distributions.
- CE‐Therapy: IMRT QA: Multiple Institution Planning and Dosimetry Comparisons
35(2008); http://dx.doi.org/10.1118/1.2963118View Description Hide Description
There is evidence that IMRT treatments may not always be as accurate as practitioners believe. In 2006, the Radiological Physics Center (RPC) reported that of the 155 institutions that had irradiated a head and neck phantom as part of an IMRT credentialing process, 54 (35%) had failed to meet accuracy criteria of 7% for dose in a low gradient region and/or 4 mm distance to agreement in a high gradient region. This experience strongly suggests that some clinics have not adequately commissioned their planning and delivery systems for IMRT. By “commissioning”, we mean beam modeling in the treatment planning system and initial verification by phantom studies that treatments can be planned, prepared, and delivered with sufficient accuracy.
Task Group 119 of the American Association of Physicists in Medicine (AAPM) has developed a specific set of tests for IMRT commissioning that are representative of common clinical treatments and pose a range of optimization problems requiring simple to complex modulation patterns. The tests include mock prostate, head and neck, and peri‐spinal geometries. Members of the group have planned and delivered the treatments using their local planning and delivery systems, and then assessed the resulting doses using broadly available dosimetry tools following a specified protocol. Measurements included ion chamber point doses and film dosimetry on selected planes for all fields irradiating the phantom. Institutions also evaluated dose distributions produced by individual fields using detector arrays, film, or EPID.
Eight institutions have reported their results with nine different combinations of planning systems and accelerators. All have passed the RPC IMRT phantom test. The summary of the preliminary data shows:
One institution identified the need to improve the beam modeling using these tests for better agreement between planned and delivered doses for IMRT.
The presentation will illustrate (1) that the percent of points passing the gamma criteria is highly dependent on the details of the implementation of the test and (2) that testing the individual fields with a gamma test can be insensitive to problems and is not sufficient for commissioning. (3) The tolerance limits based on Dose‐difference distribution, distance‐to‐agreement (DTA), and a numerical gamma index for IMRT QA are often not adequate because all these methodologies do not account for space‐specific dose uncertainty information. (4) beam modeling affects the plan and delivered dose agreement.
1. To describe the uncertainties in IMRT planning and delivery‐describe the impact of spatial and dosimetric uncertainties on the IMRTdose distribution.
2. Obtain examples of commissioning results for standardized IMRT studies that can be used for comparison with a clinic's IMRT system.
3. See how these standardized tests can be downloaded or created for local testing purposes.
4. See examples of how the gamma criterion can vary depending on details of its implementation.
5. See examples of limitation of gamma criterion testing for identifying problems with individual IMRT fields.
- CE‐Therapy: Imaging for Assessment/New Technologies
35(2008); http://dx.doi.org/10.1118/1.2962821View Description Hide Description
The clinical value of in vivo functional and physiological imaging (perfusion, diffusion, and diffusiontensorimaging) for assessment of therapeutic responses has been demonstrated in recent years. In vivo functional and physiological imaging can provide early prediction for treatment outcomes and organ and tissue complications, compared to conventional clinical methods and anatomic imaging. The advantage of early assessment is to allow for re‐optimizing individual patients' treatment plans, including decisions of total dose, modifying risks of critical normal tissue, and optimizing use of concomitant therapies. Clinical applications of perfusion, permeability, diffusion and diffusiontensorimaging are increasing rapidly.
This lecture will provide an overview of physiological origins of perfusion, permeability, diffusion and diffusiontensorimaging, as well as clinical applications, typical imaging acquisition protocols, and image processing methods. The limitations of these techniques will also be discussed.
1. Understand the physiological origins of perfusion, diffusion and diffusiontensorimaging.
2. Understand typical imaging acquisition protocols and basic image processing methods.
3. Understand clinical applications and limitations.
- CE‐Therapy: Margins in Radiotherapy
35(2008); http://dx.doi.org/10.1118/1.2962416View Description Hide Description
Conformal radiation therapy has historically used margins to account for geometrical uncertainties in the position of a target volume. The margins, in their simplest form, are simply expansions to the shape of a treatment beam, to ensure that dosimetric planning criteria are met in the presence of inter‐ and intra‐fraction setup variations. Historically, the size of the margin in a given treatment site was difficult to determine due to the available technology and the time and effort required to obtaining accurate data. Consequently, margins were estimated to accommodate a population of patients. As new technologies have emerged, target volume position errors have become easier to measure, their accuracy has increased, and the measurements can be made much more frequently. As the quantity and quality of data has increased for patient populations, and even for individual patients, the conceptual basis of employing margins has evolved. Strategies for ensuring dosimetric coverage may now be individualized to a specific patient's geometric uncertainty characteristics with customized margins, or they may incorporate geometric correction based on predefined action levels. Other strategies may incorporate continuous monitoring to gate or modify the beam. And finally, other strategies seek to eliminate margins by including the estimated geometrical uncertainty into the development of the dose distribution.
1. To provide an educational review of the technologies and methods of measuring target volume positioning errors.
2. To review methods of determining population margins from measured data.
3. To review corrective and intervention strategies for patients with individualized margins.
4. To briefly review planning strategies which seek to eliminate margins.
Conflict of Interest: DA Low: Research sponsored by Tomotherapy and Varian; DW Litzenberg: Research sponsored by Calypso Medical Technologies, Inc.
- CE‐Therapy: Protons: Planning and Delivery
35(2008); http://dx.doi.org/10.1118/1.2962331View Description Hide Description
The clinical advantages of protonbeams have become widely recognized and there has recently been a significant increase in interest for building additional proton therapy facilities. There are currently over 25 institutions worldwide treating patients with protonbeams and over 55,000 patients have been treated. There are at least 25 new facilities in various stages of planning and building. However, the fraction of patients treated with protons each year remains extremely small compared to the total number of cancer patients treated with external beamphotons and electrons. The advantage of protonbeams lies primarily in their excellent dose localization as compared to that which can be achieved using photonbeams. Due to the Bragg peak characteristic in the depth dose of protonbeams, the integral dose from proton therapy is, in general, about two times less that that for photontreatments. This allows higher doses to be delivered to target volumes, resulting in increased probabilities of local control, and lower doses delivered to critical normal tissues, resulting in decreased probabilities of treatment‐related morbidity. There are many challenges associated with increasing the accessibility of proton therapy not the least of which is the very limited number of clinical staff with knowledge of and training in proton therapy. The aim of the present Continuing Education Course is to provide a basic understanding of the rationale for proton therapy,physics of protonbeams, technology of protonbeam acceleration and transport,delivery of protontreatments,protontreatment planning and clinical results of proton therapy.
1. Understanding of the physical characteristics of protonbeams and interactions in tissues.
2. Understanding of the beam production and treatmentdelivery technology for protonbeams.
3. Understanding of the clinical commissioning of proton therapybeams.
4. Understanding of the basic principles of protontreatment planning.
5. Understanding of the clinical results for proton therapy.
- CE‐Therapy: Tomotherapy
TH‐SAMS‐AUD B‐01: Introduction To: Quality Assurance for Advanced RT Technologies—The Challenge for RT Clinical Trials35(2008); http://dx.doi.org/10.1118/1.2962805View Description Hide Description
We as medical physicists have a crucial role to play in ensuring that all patients on radiotherapy protocols are treated comparably. Without this comparability, the validity of outcome results from the pooled patient data may be jeopardized. Advances in radiation therapy technology and delivery techniques have naturally led to the desire to incorporate such new tools into clinical trials, yet standardized quality assurance (QA) procedures are not fully developed and widely practiced. Although several task groups within the AAPM have been formed to set standards for QA for these new technologies, a major challenge is to conduct clinical trials that involve both the old and new technologies without overwhelming individual physicists with additional testing. National and international multi‐institutional clinical trials uniquely challenge the medical physics community to maintain comparability while at the same time requiring or permitting patient treatments that incorporate advanced technologies such as IMRT, image guided radiotherapy,imagefusion, and other techniques.
The AAPM Working Group on Clinical Trials presents this continuing education symposium in order to discuss the efforts underway to design QA methods for advanced radiotherapy technologies especially in the context of clinical trials with the intent to address the issue of comparability and standardization of protocol data. We will present the work of Task Group 113, an important player in these efforts, on providing guidance as to physics practice standards for QA for radiotherapy clinical trials. The task group's recommendations on QA procedures and reporting methods are intended to facilitate highly consistent protocol treatments and data submission.
The Working Group on clinical trials has identified several topics that pose significant challenges with respect to consistency of physics practices: dose calculations with heterogeneity corrections, localization verification, imagefusion techniques, and the treatment of moving targets. In this course, the history and the current state of the art will be described for each topic. The discussion about these areas should be of interest whether or not one is involved in clinical trials.
1. Understand the quality assurance issues facing Medical Physicists using advanced technologies and how these relate to clinical trial data validity.
2. Learn what Task Group 113 is doing to address the accuracy and consistency of data we send to quality assurance review centers.
3. Understand the problems and potential solutions to controversies in quality assurance measures for imagefusion, target motion, patient localization, and heterogeneity corrections.
35(2008); http://dx.doi.org/10.1118/1.2962806View Description Hide Description
Imaging studies acquired at multiple times and using different modalities are important components to many clinical trials. Imaging is used for staging and protocol eligibility, for radiation therapy target definition, for adaptive radiation treatmentdelivery, for assessing response to therapy, and for outcome analysis. Currently co‐registration of CT, MR and PET scans may be important for any of these purposes; in the future, molecular and biomarker imaging may be incorporated.
The challenges for the QA centers are to verify that institutions participating in protocols requiring image registration have the tools and expertise to perform the registrations, and to verify the appropriate registration for individual protocol patients. There are many software systems, many with multiple methods, available for image registration.
One method to credential institutions is by benchmarking. QARC's “image fusion” benchmark requires the institution to download a DICOM MR and a DICOM CT scan set. The datasets are to be registered, the small lesion is to be outlined on the MR scan, and the geometrical center of the lesion on the CT scan is to be reported (lesion not visible on CT). Results from more than 50 institutions will be discussed.
An increasing number of protocols require PETimaging. Registration of PETimaging is problematic, except for PET/CT. Since the DICOM standard does not include specifications for SUV calculations, currently only ACRIN, by using the manufacturers' workstations, is able to receive PETimages and recalculate SUVs. Ideally these PETimages would be registered with the planning CT in radiotherapy protocols.
More and more protocols propose requiring IGRT, particularly for treatments with few fractions. For protocol participation, institutions need to demonstrate the reproducibility and accuracy of the imaging system used to adapt the daily treatment to the daily target position. Extensive questionnaires (QARC) and submission of representative patient data (RTOG) are required by the QA centers. The variety of systems — MV CT, kV CT, Tomotherapy, Cyberknife, ultrasound — provide a challenge for the QA center.
An even greater challenge is how to provide QA for individual patient treatments. If CT/CT or CT/MR registration is used for target delineation, assessment of the registration presents the QA center with several questions. Should the QA center redo the registration? What tools can be developed to register and verify CT/PET registration? For adaptive radiotherapy, what is the benefit of reviewing the daily assessment of required repositioning? Is the benefit worth the cost of such an effort?
1. Understand the issues faced by the QA centers in reviewing image registrations.
2. Understand the difference between credentialing and providing individual patient QA for image registration.
3. Become familiar with the current strategies of QA for image registration by the QA centers.
TH‐SAMS‐AUD B‐03: Requirements for Addressing Respiratory Motion in Cooperative Group Clinical Trials (SAM Session)35(2008); http://dx.doi.org/10.1118/1.2962807View Description Hide Description
In mid‐2006, the National Cancer Institute (NCI) published updated guidelines for the use of intensity‐modulated radiation therapy(IMRT) on clinical trials, specifically when the target volume included the thoracic region or other areas in which respiratory motion could have a significant effect. In addition to requiring heterogeneity corrections, the NCI now requires that the clinical protocol address the localization and immobilization of both the patient and the tumor.Imaging must be performed in a manner that provides a representation of the target volume without motion artifact. Procedures must be defined to document reproducible daily position of the patient and target. Some form of credentialing is required.
The Radiological Physics Center (RPC) has been enlisted to participate in the credentialing process for institutions participating in certain cooperative group trials in which respiratory motion is an issue. To accomplish this, the RPC has constructed several phantoms that mimic the thoracic and abdominal region, and which can be placed on a moving platform to simulate respiratory motion. The combination of phantom and moving platform have been used to evaluate compensation techniques for respiratory motion at several institutions. The techniques employed and the results of these measurements will be described as well as those reported in the literature.
1. Review the structure supporting cooperative group clinical trials in the US.
2. Become familiar with the NCI guidelines for the use of IMRT in clinical trials.
3. Learn about the effects of respiratory motion during thoracic treatments.
4. Understand the information derived from the RPC's moving anthropomorphic phantoms.
This research is supported by grants CA 10953 and 81647 awarded by NCI, DHHS.
35(2008); http://dx.doi.org/10.1118/1.2962808View Description Hide Description
Clinical trials rely on accurate dose reporting, both for the planning target volumes and organs at risk (OAR). Until recently, clinical trials have not mandated that heterogeneity corrections be applied in dose calculations. Therefore history of prescription and reported doses has been for homogenous water equivalent media. The reticence is attributed to lack of confidence in commercial treatment planning algorithms and in lack of direction as how to change prescriptions when accounting for heterogeneous media. Thorax irradiation is the most challenging example of where corrections and prescription changes are difficult but necessary. Two well reported studies, RTOG‐8808 and RTOG‐9311, required complementary parallel calculations performed. One set was the prescribed and treated homogeneous (water) based calculations, and the other was retrospective heterogeneous CT‐based calculations, but using the homogeneous based MU. The calculations demonstrated major variations in the doses that would have been reported depending if heterogeneity corrections were exclusively used. This was confirmed by dosimetric studies showing the failure of algorithms of the 1990s, particularly in regions of non‐equilibrium. As OAR, particularly lung volume, were often the limiting factor, dose calculations to the lung itself had to be accurate. High energy‐small fields had the largest deviations. The commercial introduction of superposition and Monte Carlo algorithms has remedied the situation by providing accurate calculations, provided they are implemented properly. Simultaneously, publication of AAPM's Report of TG‐65 (Inhomogeneity Corrections) gave direction to physicists as how to work with clinician partners to transition to correction based plans and change prescriptions accordingly.
1. The history of corrections for clinical trials.
2. Progression of algorithms.
3. Methods for making the transition to using heterogeneity corrections.
35(2008); http://dx.doi.org/10.1118/1.2962809View Description Hide Description
Paralleling the introduction of Intensity Modulated Radiation Therapy(IMRT) in the early to mid 1990s, Image Guided Radiation Therapy(IGRT) is an important but problematic new tool for the RadiationOncology community. The challenges are similar to IMRT in that IGRT is a general classification that covers many different approaches with numerous variations. Where IMRT ranges from tomotherapy to conventional MLC‐based dose delivery with many different treatment planning approaches, IGRT covers a broad spectrum of techniques ranging from stereoscopic x‐ray imaging with rigid‐body registration to cone‐beam volume imaging with deformable fusion. Thus, like IMRT, guaranteeing the safe and effective use of this new modality in a clinical trial setting will require procedures that are as comprehensive as the ones currently in place for IMRT. As quality assurance techniques are developed for routine clinical use of advanced technologies like IGRT, they must also be appropriately standardized for use in clinical trials.
Image Guidance is defined for RTOG protocols as the steps of obtaining daily in‐room images of the patient in the treatment position, matching or fusing these images to the ones obtained during the treatment planning process, and the procedure of manually or automatically changing the patient's position based on the fusioninformation. Notice that this description does not consider the patient as a deformable object. Using this simple definition, a number of Radiation Therapy Oncology Group (RTOG) protocols have employed or are including IGRT for targeting the lesion. These protocols require institutions to verify their IGRT methodology through a credentialing process. This process is aimed at guaranteeing that each institution understands the protocol requirements relative to the use of their fusion software or manual shift capabilities.
This presentation will discuss the process used by the RTOG to credential institutions for the use of IGRT in their protocols, and it will present the problems and considerations that will have to be addressed as the above definition of IGRT expands to include moving targets and deformable fusion.
35(2008); http://dx.doi.org/10.1118/1.2962810View Description Hide Description
The goal of AAPM Task Group 113 is to provide guidance to physicists, QA centers, and others involved in clinical trials on methods to improve the consistency and quality of data generated for trials involving external beam radiotherapy.
To date, there are no universally agreed upon standards for the physics practices related to clinical trials. In addition, as treatment techniques become more sophisticated, it is even more challenging to comprehensively maintain consistency across multiple institutions. Since hundreds of institutions may be involved in clinical trials, it is critical to review the entire treatment planning and delivery process and to identify areas where improvements can be made to ensure that high quality and consistent data are acquired from all institutions treating patients on clinical trials.
This presentation will focus on factors that impact data quality for the treatment planning and delivery process. In addition, methods to help individual physicists improve the consistency of clinical trials will be discussed. The scope of the task group includes image acquisition for volume definition, treatment planning systems, patient localization, treatment guidance and delivery, and credentialing for clinical trials.
1. To describe the goals of TG♯113 Physics Practice Standards for Clinical Trials.
2. To highlight factors that directly impact clinical trials that involve IMRT and IGRT.
35(2008); http://dx.doi.org/10.1118/1.2962811View Description Hide Description
Helical tomotherapy using the HiArt system can provide highly conformal dose distributions through the implementation of helically deliveredintensity modulated radiation therapy(IMRT). The TomoTherapy HiArt system uses a 6 MV linear accelerator mounted on a ring gantry with a simultaneously translating couch. The system also provides image guidance via megavoltage CT. Since this design is significantly different than traditional medicallinear accelerators, a unique quality assurance program must be implemented to thoroughly test the HiArt delivery system.
This course will provide an overview of the HiArt system components, acceptance testing and commissioning, beam “twinning” for recommissioning of an existing machine to match the TomoTherapy “gold” standard, and basic quality assurance recommendations. The use of ion chamber and diode arrays for patient‐specific delivery QA will also be discussed.
1. Understand the core concepts of helical tomotherapy.
2. Understand the commissioning process for a new HiArt system and the beam “twinning” and recommissioning of an existing HiArt system.
3. Understand the machine QA procedures for helical tomotherapy.
4. Understand the helical tomotherapy patient‐specific delivery QA process, including the use of ion chamber and diode arrays.
Conflict of Interest: Our group holds a research grant from TomoTherapy, Inc.