Index of content:
Volume 34, Issue 6, June 2007
- Therapy Continuing Education Course: Room M100F
- CE‐Therapy: Biological/clinical Outcome Models in RT Planning
34(2007); http://dx.doi.org/10.1118/1.2761306View Description Hide Description
The use of mathematical models to summarized clinical or biological endpoints with respect to the distribution of dose throughout an organ or tissue has great appeal. At its best, the overall cumulative effects of all parts of a heterogeneously irradiated object could be summarized in terms of a clinically relevant outcome such as a tumor control probability (TCP) or a normal tissue complication probability (NTCP). Further, it could be anticipated that a treatment planner would want to incorporate such information directly into the optimization of treatment planning parameters.
Despite this appeal, integration of these concepts into mainstream treatment planning has been slow in coming. Parameterization of the models is conceptually simple, requiring input data consisting primarily of dose, volume and outcome information from groups of patients. However, uncertainties in accumulated total effective dose and differential irradiated volumes together with heterogeneities in biological responses can make these determinations difficult. At best, it has been possible to obtain broad “population” based model parameters for some organs and tumors for “groups of similarly‐treated patients”. In general, as used today, these models are not within themselves (i.e., without additional stratification factors) “predictive” of outcome for “individual” subjects, nor can their use be generally extrapolated to the treatment of populations with techniques that vary greatly from those originally used.
However, disclaimers aside, the appeal remains great, and real progress has been made. In this session we will present some of the basic concepts associated with the models. Examples will be given as to how the models accommodate the responses of different tumor types and so‐called serial and parallel normal tissues. We will show how (as currently used) implementation of the models in evaluation or planning generally first requires reduction of a complex dose distribution (or DVH) into an equivalent “uniform” total (or partial) object dose.
Examples where the biological models appear to work well to describe the response of groups of patients will be provided. Specifically, the use of NTCP models for planning the treatment of tumors surrounded by volume effect normal tissues will be demonstrated, as will the use of EUD to allow rational heterogeneous irradiation of target volumes.
Some technical details associated with the implementation of biological models into IMRT planning systems will be discussed. Since mathematical structures of biological models are nonlinear, an optimization algorithm that can explicitly handle nonlinear objective and constraint functions is important. We will describe various ways of incorporating the models into optimization problems.
This session will be concluded with a short survey of existing software tools that utilize the biological models for dose‐response data analysis, plan evaluation, and IMRT plan optimization.
1. Understand the basis and statistical nature of standard NTCP and TCP models.
2. Recognized that dose distribution reduction remains a basic component of their implementation and understand how this is accomplished.
3. Appreciate that as currently used, most results apply to “populations” of “similarly treated” patients.
4. Understand numerical issues of implementing and using the biological models within optimization systems.
- CE‐Therapy: Daily Location III: Tomotherapy
- CE‐Therapy: IMRT Site Specific — II: H&N, CNS
34(2007); http://dx.doi.org/10.1118/1.2761471View Description Hide Description
Intensity modulated radiation therapy(IMRT) for the central nervous system(CNS) is being used more frequently in radiationoncology clinics. There are two general situations that the treatment of CNS disease may benefit from the use of IMRT compared to conventional, three‐dimensional conformal radiation therapy: 1) when multiple critical structures confined within the intracranial vault are to be avoided, one may desire an optimal dose distribution that allows for the dose to these structures to be minimized, and 2) since high‐grade gliomas tend to recur locally, IMRT should allow for dose escalation proportional to the corresponding heterogeneous cell populations. Based on the anatomic location of the treatment volumes, one can envision examples where IMRT could be of benefit. Patients with a concave or irregularly‐shaped target in a frontal lobe may require IMRT in order to spare the adjacent globe and any uninvolved optic apparatus. In patients with well‐lateralized tumors involving the brain parenchyma, complete sparing of the contralateral hemisphere is desirable. Patients with infiltrative gliomas traditionally have large margins placed around the treatment volumes, and these may often encompass uninvolved critical normal structures. For such cases, IMRT may allow for non‐uniform reduction of the treatment volume around these normal structures. The primary goal of this presentation is to provide a practical overview of IMRT for the CNS.
Though much attention has been given to the inverse planning and quality assurance aspects of IMRT, one should have an adequate understanding of the entire process; from proper patient selection to positioning/immobilization and continuing through treatment. A discussion of the steps of the CNSIMRT process will include: patient selection, immobilization, recommended imaging acquisitions, structure delineation, planning strategies/parameters, dose objectives, plan evaluation, QA, and potential delivery issues. Guidelines and practical examples for each component of this process will be presented.
To gain further familiarization of CNSIMRT, one should review the corresponding technological and clinical outcome literature. Comparisons to conventional radiotherapy methods will be examined in terms of technique, dosimetry and clinical outcome. Finally, current research and future directions of CNSIMRT will be introduced such as the novel use of sophisticated imaging techniques for improved structure definition, patient positioning and dose modulation.
1. To understand the general practice of CNSIMRT from patient selection through actual treatment.
2. To become familiar with specific details pertaining to the CNSIMRT process through several illustrative examples.
3. To be introduced to some of the research and future directions of CNSIMRT.
Research supported, in part, by Varian Medical Systems.
34(2007); http://dx.doi.org/10.1118/1.2761472View Description Hide Description
The purpose of this presentation is to discuss issues in IMRT treatments for head and neck cancers. The main focus will be on the details related to the planning process such as, immbolization, imaging and setup management, treatment planning, and plan evaluation. The conformal nature of IMRTdose distributions requires additional consideration on the degree of immbolization and expected reproducibility of setup. Custom neck molds, masking systems and additional shoulder constraints are required to maximize reproducibility of the head, chin, and clavicals (supraclavicular nodes). Even with these constraints, daily variability can be expected and the treatment plan should account for those effects. Localization tools such as on‐board kV planar imaging and cone‐beam CT can be used daily to aid in localization and patient set‐up. Target and normal tissue segmentation are very important in the planning process and must be considered in detail by the physicist. Various imaging modalities are frequently used. Contrast enhanced CT and MRI‐CT fusion is helpful for primary tumor segmentation. Fused 18FDG PET‐CT images can be used to identify positive neck nodes but lack anatomic definition and are not always useful for defining the primary tumor. Before treatment planning begins, a dialogue with the physician can reduce the number of IMRT plans that are attempted to arrive at the best plan. The conversation with the physician should contain information about dose/volume tolerances of normal tissues and other patient‐specific issues (e.g., previous treatment, chemotherapy, or already compromised tissues). With IMRTtreatment planning there are many more techniques at the physicist's disposal to develop the best treatment plan compared to conventional planning. Evaluating IMRT plans is a determination of tradeoffs. An important principle regarding target coverage is the trade‐off between dose conformity and dose heterogeneity across the target. It is essential to be realistic in the expectations of IMRT and be prepared to accept some dose to critical structures (but keeping them below tolerance) in order to get better target coverage than a conventional plan would provide. Slice‐by‐slice evaluation of isodose coverage for the location and magnitude of hot and cold spots is required during plan evaluation. Before starting treatment, a set‐up verification step is typically helpful, during which the immobilization system and isocenter location are checked. Orthogonal DRR images of the isocenter(s) location can be reproduced by simulator images for better visualization of bony landmarks. Kilovoltage and cone‐beam CTimaging techniques are more prevalent in the treatment room for this purpose.
1. Understand issues related to patient immobilization.
2. Identify normal tissues and know their dose/volume constraints.
3. Describe several planning techniques to achieve the best dose distribution.
- CE‐Therapy: Integration of the Health Enterprise in Radiation Oncology (IHE‐RO)
34(2007); http://dx.doi.org/10.1118/1.2761194View Description Hide Description
Initiated in 2005, Integrating the Healthcare Environment for Radiation Oncology (IHE‐RO) is a multi‐society, multi‐vendor effort to improve the safety, reliability, and integration of computer and information systems within the radiation oncology arena. IHE‐RO works to accomplish this by coordinating the use of standards such as DICOM and HL7 to effectively exchange information between diverse computer systems involved in the process of planning and delivery of radiation therapytreatments. It attempts to remove ambiguity where it exists in these standards by defining consensus profiles to solve real‐world situations.
Each IHE domain (radiology, cardiology, radiation oncology, …) identifies areas where improvements need to be made in the sharing / exchange of information between disparate systems. An IHE Planning Committee then defines a real‐world use case illustrating this process and a trial Integration Profile for improving it. This profile is then discussed by the Technical Committee, which defines the specific standards and methods for exchanging information that will be used to satisfy the needs of the profile and use case. Finally, the Integration Profile and detailed implementation specifics are published in the domain's Technical Frameworks documentation.
Once published, those vendors participating in the IHE process develop / refine products to meet the Integration Profile's requirements. Testing occurs via test tools developed for the profiles and then demonstrated in a formal Connectathon, held under the auspices of the society sponsoring the domain. Companies that successfully demonstrate their compliance with the profile are then included in a public demonstration, held at the society's annual meeting. The complete process from profile initiation to public demonstration typically takes 20–24 months.
In this session, the progress of the IHE‐RO effort will be reviewed. The profile selected for demonstration at the ASTRO 2007 Annual Meeting will be discussed. The proposed profiles for 2008 will be compared, and the rationale for those selected for inclusion in the 2008 demonstration will be given. Profiles developed within other IHE domains, such as Information Technology Infrastructure, will also be discussed.
1. To describe the structure and purpose of the IHE effort, including a brief history of IHE and the formation of the IHE‐RO effort.
2. To review the development process of the 2007 IHE‐RO profile; how it was developed, its benefits, and its limitations.
3. To discuss the profiles currently under consideration for future IHE‐RO efforts, particularly the 2008 public demonstration.
4. To describe efforts in other IHE domains that may influence the development of information systems in radiation oncology.
- CE‐Therapy: Protons: Planning and Delivery
34(2007); http://dx.doi.org/10.1118/1.2761204View 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 50,000 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 significantly less that that for photontreatments. This allows higher doses to be delivered to target volumes, resulting in increased rates of local control, and lower doses delivered to critical normal tissues, resulting in decreased rates 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. the physical characteristics of protonbeams and interactions in tissues.
2. the beam production and treatmentdelivery technology for protonbeams.
3. the clinical commissioning of proton therapybeams.
4. the basic principles of protontreatment planning.
5. the clinical results for proton therapy.
- CE‐Therapy: QA for Imaging System Used for Planning (CT, PET, MR)
34(2007); http://dx.doi.org/10.1118/1.2761611View Description Hide Description
Imaging for radiation therapytreatment planning has different goals than diagnosticimaging.Quality assurance (QA) of imaging devices (CT,PET, MR) which are used for radiation therapyimaging will therefore have different or additional goals compared to QA for diagnosticimaging purposes. Use of PET and MR imaging in radiation therapy is constantly increasing and reliable performance of these imaging modalities is important to avoid potentially significant errors.
Quality assurance for CTscanners used for radiation therapy scanning is relatively well established and defined. This process remains to be adequately defined for PET and MR scanners that are used for treatment planning. Evaluation of image quality of CT,PET, and MR scanners is generally adequately addressed by procedures which were established for diagnosticimaging. Design of QA protocols for radiation therapy scanning should be founded on procedures which are used for diagnosticimaging. Evaluation of mechanical accuracy and image spatial integrity is unfortunately not a major concern in diagnosticimaging and these parameters are often not sufficiently addressed in diagnostic QA protocols. All three imaging modalities have multiple potential sources of spatial and geometric errors and understanding of these parameters is necessary for design of an effective quality assurance program. The design of QA programs for these devices will be affected by the location of individual scanner and distribution of its utilization for diagnostic and radiation therapyimaging.Scanners which have dual purpose (diagnostic and treatment planningimaging) should have a QA program designed jointly by diagnostic and radiation therapy physicists to ensure that the program meets the needs of both groups.
The quality assurance for these imaging modalities in the radiation therapy goes beyond the QA of the scanners and should include evaluation of implementation of images in the treatment planning process. This should include evaluation of data transfer, image registration, potential degradation in image quality, image distortions, and evaluation of process for delineation of tumor and normal structure volumes. MR and PETimages can contain biologically active regions which may not correlate with any readily visible anatomic features. Correct identification and use of these regions in the treatment planning process should be a major concern of the QA program.
This lecture will provide an outline and description of QA program for CT,PET, and MR scanners used in radiation therapy. The fundamental goals of such program will be described and information which can be used for establishment institution specific QA programs will be provided.
1. Describe goals of QA programs for CT,PET, and MR scanners used for radiation therapyimaging.
2. Describe QA process for individual imaging devices.
3. Describe a concerns for verification of correct implementation of these imaging modalities in the treatment planning process.
34(2007); http://dx.doi.org/10.1118/1.2761612View Description Hide Description
Quality assurance (QA) for Intensity Modulated Radiation Therapy(IMRT) and Image Guided Radiation therapy(IGRT) is an essential component of the clinical treatment process. The goal of QA is to ensure that the prescribed doses are delivered to the target volume, and that the surrounding critical structures are spared within an acceptable tolerance. There are many sources of error that can arise during IMRT planning and delivery. However, it is ultimately the responsibility of the Medical Physicist to ensure that the prescribed doses agree with the delivered doses. Differences between planned doses and delivered doses in IMRT and IGRT can originate from errors in the treatment planningmodel, errors in the treatment delivery system, patient setup errors, anatomical changes in the patient, and/or physiological changes in the patient.
The first step in the IMRT QA process is to evaluate the treatment‐planningmodel as part of the initial IMRT commissioning, and again after major software upgrades. The AAPM Task Group 119 (Writing group on IMRT QA) is in the process of developing site‐specific acceptance and commissioning tests for treatment planning and delivery systems. These tests evaluate the IMRT system using standardized test plans for multiple geometric and anatomical targets. Using these tests, calculated and measured doses could be compared by medical physicists using their planning and delivery system. Thus providing a standardized mechanism for testing the entire IMRT process from planning to delivery.
An additional source of error in IMRT is the uncertainty in the position and shape of the target volume. The use of image‐guided radiation therapy can help minimize, but will not eliminate these errors. Changes in patient setup, normal physiological changes, tumor response, normal tissue response, and weight loss can cause changes in the position of the target volume relative to the surrounding critical structures. It is important that the Medical Physicist know how to identify these changes and determine when a new treatment plan is needed to adapt for these changes.
This continuing education course will discuss commercially available dose measurement tools, phantoms, and techniques for performing acceptance testing, commissioning, and routine quality assurance for the IMRT and IGRT process. Types of commonly encountered errors will be discussed, with a special emphasis on the lessons learned and manpower requirements.
1. To understand the issues surrounding IMRT and IGRTquality assurance.
2. To identify potential sources of errors in IMRT and IGRTquality assurance.
4. To review the tools used in IMRT and IGRTquality assurance.
4. To understand the impact of target localization and patient positioning.
- CE‐Therapy: Quality Assurance for IMRT and IGRT
34(2007); http://dx.doi.org/10.1118/1.2761627View Description Hide Description
Image‐guidedradiation treatment(IGRT) units are now available in the community and are capable of routine clinical use, offering unprecedented level of precision and accuracy in treatment delivery. These systems bring a substantial change in clinical practice for all the disciplines involved in radiation medicine. One can now correct patient position using image information displaying not only bony anatomy and airways, like portal imaging, but also implanted markers, soft tissue structures within the patient, and sometimes the target to be irradiated. Growing experience with kilovoltage IGRT systems has demonstrated the ability to verify, on a daily basis, the position of internal anatomy structures with respect to the treatment beam geometry for several anatomical sites. Kilovoltage IGRT systems further allow, using daily imaging sessions, on‐line correction of patient translations and rotations, and the comparison for successive daily volumetric images permits to track changes of anatomy through the course of therapy. Introducing kV systems within busy radiation therapy clinics requires thoughtful testing and quality assurance protocols (QA) of the device, and judicious modification of existing radiation therapy processes and protocols. While the modes of use of these novel systems will continue to evolve into the distant future, their performance needs to be of the highest level, as they will be depended upon in the treatment process.
There are two key features of the kilovoltage IGRT systems require particular attention: geometric accuracy and image quality. First, the kilovoltage IGRT system may not share a common central axis with the megavoltage treatment beam; therefore, the geometric relation of the kilovoltage imaging datasets to the megavoltage treatment beam must be assessed and monitored to ensure adequate localization, scaling, and geometric accuracy. Second, image quality metrics define the ability of the kilovoltage IGRT system to consistently produce an image of sufficient quality to localize the structures of interest. A well‐planned QA program integrates closely the IGRT system procedures with linac procedures described in accepted QA standards such as the AAPM task group 40 report.
This lecture will present a brief review of kilovoltage IGRT systems, and will focus on a suitable QA program, with special emphasis on issues germane to the system and the clinical processes relying on its use. Daily and monthly procedures, with phantoms constructed for these QA activities, will be suggested, and some quality assurance metrics, with their associated tolerance levels based on three years of experience on such devices will be presented. These levels are based on data accumulated over four years of experience on ten linear accelerators equipped with kilovoltage IGRT devices in our multi‐vendor environment. Successful strategies for clinical implementation of IGRT will also be discussed.
1. Understand the technical issues related to kV systems.
2. Understand the impact of kV systems on clinical processes.
3. Present a comprehensive commissioning protocol and QA program for kV systems.
This work is supported, in part, by a research grant from Elekta Oncology Systems.
- CE‐Therapy: RPC programs
34(2007); http://dx.doi.org/10.1118/1.2761486View Description Hide Description
Purpose: To describe the mission and activities of the Radiological Physics Center (RPC). Method and Materials: The RPC was founded in 1968 under an agreement between the AAPM and the Committee for Radiation Therapy Studies (CRTS). The agreement called for the AAPM to solicit applications to form a QA center that would be a resource in radiationdosimetry and physics for cooperative clinical trial groups and all radiotherapy facilities that deliver radiation treatments to patients entered onto cooperative group protocols. The RPC has functioned continuously for 38 years to support medical physicists and radiation therapy departments. Results: The RPC's mission has changed only slightly over the years. The primary responsibility is to assure NCI and the cooperative groups that the participating institutions have adequate quality assurance procedures and no major systematic dosimetry discrepancies, so that they can be expected to deliver radiation treatments that are clinically comparable to those delivered by other institutions in the cooperative groups. To accomplish this, the RPC monitors the basic machine output and brachytherapy source strengths, the dosimetry data utilized by the institutions, the calculation algorithms used for treatment planning, and the institutions' quality control procedures. The methods of monitoring include on‐site dosimetry review by an RPC physicist, and a variety of remote audit tools. During the on‐site evaluation, the institution's physicists and radiationoncologists are interviewed, physical measurements are made on the therapy machines, dosimetry and quality assurance data are reviewed, and patient dose calculations are evaluated. The remote audit tools include 1) mailed dosimeters (TLD) evaluated on a periodic basis to verify output calibration and simple questionnaires to document changes in personnel, equipment, and dosimetry practices, 2) comparison of dosimetry data with RPC “standard” data to verify the compatibility of dosimetry data, 3) evaluation of reference and actual patient calculations to verify the validity of treatment planning algorithms, and 4) review of the institution's written quality assurance procedures and records. Mailable anthropomorphic phantoms are also used to verify tumordose delivery for special treatment techniques. Any discrepancies identified by the RPC are pursued to help the institution find the origin of the discrepancies and identify and implement methods to resolve them. Conclusion: While conducting these reviews, the RPC has amassed a large amount of data describing the dosimetry at participating institutions. Representative data from the monitoring programs will be discussed and examples will be presented of specific instances in which the RPC contributed to the discovery and resolution of dosimetry errors.
The RPC is supported by PHS grants CA 10953 and CA 81647 awarded by NCI, DHHS, and by an educational grant from Varian Medical Systems.
1. Become familiar with the activities of the Radiological Physics Center.
2. Know how to contact the RPC for assistance or collaboration.
3. Understand the role of the RPC in monitoring institutions that participate in clinical trials.
4. Review common errors and misconceptions regarding dosimetry, credentialing requirements, and other issues.