Volume 34, Issue 6, June 2007
Index of content:
- Joint Imaging/Therapy Symposium: Room M100J
Spatio‐temporal Imaging for Radiation Treatment Planning and Delivery
34(2007); http://dx.doi.org/10.1118/1.2761274View Description Hide Description
This presentation surveys imaging systems, their limitations and expectations for target and organ‐at‐risk position determination, delineation and respiratory motion estimation. Discussion will focus on systems that are in current clinical use. Imaging techniques at simulation usually attempt to use the same patient breathing conditions as at treatment, among them, breath hold, free breathing, coached breathing, or abdominal compression. CT remains the dominant standard for anatomical imaging of external beam radiotherapy simulation. CT acquisition techniques for motion estimation include breath hold at different inspiration levels, or more recently, respiration‐correlated CT (RCCT), involving retrospective sorting of axial images by means of a respiration signal. A limitation of RCCT is that images at a given position along the patient are confined to a single respiratory cycle, and assumes that the breathing pattern is repeatable, which is known to be violated to some extent depending on the patient. Further, images are acquired over several cycles and resorted into a single one; thus cycle‐to‐cycle changes in breathing pattern lead to artifacts. Coached breathing attempts to achieve more repeatable breathing and has shown varying degrees of improvement in some patients. Breath‐hold CT fidelity is similarly dependent on breath‐hold repeatability. Ideally imaging over several breath cycles is desirable, but imagingdose imposes limitations with RCCT, while patient fatigue limits breath‐hold CT. A possible future direction of development is to complement CT with modalities that can image over several cycles with little or no additional dose. For example, repeat MRI in the sagittal plane provides not only a self‐consistent image in terms of respiratory motion but also an estimate of cycle‐to‐cycle variation in motion extent, which is valuable for evaluating the sensitivity of a treatment plan to such variation.
1. Understand the current technological advances in radiotherapyimaging at simulation to provide spatial information and respiratory motion estimation;
2. Understand the limitations, current expectations, and possible further improvements of these imaging systems.
34(2007); http://dx.doi.org/10.1118/1.2761275View Description Hide Description
Functional imaging is being increasingly used in radiation therapy for target definition and treatment planning. In this talk I will summarize recent advances in functional and molecular imaging techniques and discuss various issues related to the integration of the newly emerged imaging data into radiation therapy planning. In particular, techniques of time resolved 4D PET acquisition will be discussed and a few method of enhancing 4D PET images will be described. It is anticipated that the new imaging modalities will make significant impact in cancer diagnosis, staging, treatment planning, and monitoring of therapeutic response. The potential impact of biologically conformal radiation therapy (BCRT) or biologically guided radiation therapy (BGRT) will be discussed. Finally, issues related to the quality assurance of functional and molecular imaging and BCRT will also be addressed.
1. Introduce the concept of functional and molecular imaging.
2. Illustrate the steps involved in integrating molecular imaging such as PET and MRSI into treatment planning process.
3. Introduce PET/MRI/MRSI and CTimage fusion techniques (including deformable image registration).
4. 4D PET data acquisition and image enhancement.
5. Provide an overview on recent advances in PET/CT and MRSI, and update on the development of new PET tracers and data acquisition techniques.
This work was supported in part by NCI 5R01 CA98523‐01.
34(2007); http://dx.doi.org/10.1118/1.2761276View Description Hide Description
Regardless of the degree to which positioning is maintained later in treatment, the critical step in the radiation therapy process involves definition of the initial patient model. Many factors influence this process, most notably the sources of differential contrast in images used, the knowledge and experience of the users defining both normal tissue as well as targeted structures, and distracting factors such as organ movement and imaging artifacts. Significant attention has recently focused on the interobserver variation in target definition, with differences observed that exceed the gains expected through in‐room target localization and potentially through gating/tracking. While Radiation Oncology departments are consumers of advanced imaging information, we have yet to find ways to truly optimize imaging to aid in consistent definition of targeted and avoidance tissues.
The objectives of this talk are to:
1. Review the process of initial definition of target and avoidance tissues.
2. Discuss observed variances in target definition.
3. Describe the impact of motion and advances such as 4DCT in the process.
4. Suggest potential areas for improving consistency in these processes.
34(2007); http://dx.doi.org/10.1118/1.2761277View Description Hide Description
Treatment planning should be based on a high fidelity representation of the patient's anatomy, as it will be at time of treatment. The imaging setup (couch, immobilization, alignment) should therefore be representative for the treatment situation. When basing a treatment plan on a single scan (which is current clinical practice), the optimal imaging strategy is therefore to create an anatomical model that is as close as possible to the “average” anatomy. For random organ motion, plan optimization can therefore be achieved by averaging the geometry of multiple scans (i.e., adaptive radiotherapy). For periodic motion it has been proposed to use a scan with the organs as close as possible to their time‐weighted average position — by selecting a single scan out of 4DCT. Using these methods, the systematic errors due to treatment preparation are minimized and the dose distributions will be very close to a full 4D planning (using all scans out of a 4DCT scan). Using image guidance some other error sources can be eliminated. However, even with image guidance there are residual errors: such as uncertainty in GTV and CTV delineation, in image registration, and in setup correction and uncertainty due to intra‐fraction motion. Currently, simple margin recipes are used to estimate the correct CTV‐PTV margin such that the net effect of all these uncertainties does not compromise the goal of the treatment: eradicate the tumor while sparing normal tissues. One should be aware, however, that the most simple margin recipes are based on many assumptions: such as Gaussian distributions, penumbra width in water, systematic error SD > random error SD, and plans with a more or less uniform dose distribution. In case of image guidance for lungtumors all of these assumptions break down, and simple recipes typically will overestimate the required margin. Based on a more detailed analysis, it appears that the margin that can be used for hypofractionated lungradiotherapy can be very small (1 cm or less), even for large respiratory amplitudes (2 cm).
1. Understand the need for a representative planning CT, i.e., minimize systematic errors.
2. Understand the difference between systematic and random errors, and the effect that respiratory motion has on the delivery of radiotherapy.
3. Understand the need for margins, even in case of image‐guided.radiotherapy.
4. Understand the derivation of margins for image‐guidedradiotherapy of lungcancer.
34(2007); http://dx.doi.org/10.1118/1.2761278View Description Hide Description
34(2007); http://dx.doi.org/10.1118/1.2761279View Description Hide Description
The problem of intrafraction tumor‐target positioning can be divided into two separate processes: (1) estimating the real‐time target position and (2) repositioning the beam to account for intrafraction target motion. Several solutions exist for both target position estimation and beam repositioning, however in principal any method of position estimation could be integrated with any method of beam repositioning. Note that beam repositioning can include moving the target to align with the beam (e.g. couch motion), which in the target reference is the same as moving the beam to align with the target.
There are several common features in target position estimation systems. First, that in the absence of a real‐time volumetric imaging system, the target position is estimated from surrogates and thus there is uncertainty in the position of the target with respect to the surrogates. Second, for all but EPID‐based methods target position estimation is independent of the treatment beam and therefore careful quality assurance is required to ensure the accurate position estimation with respect to the treatment beam.
There are also several common features of the beam repositioning systems. First, control systems with secondary feedback are required to ensure accurate and precise real time mechanical motion. Second, that there is a delay between the target motion and the beam repositioning. This delay causes delay‐time dependent errors which can be reduced with prediction algorithms.
The various target position estimation and beam repositioning processes either in development or available for clinical use will be described and contrasted.
1. Understand the separation of the target position estimation and beam repositioning processes.
2. Understand the advantages and disadvantages of several real‐time target position estimation systems.
3. Understand the advantages and disadvantages of several beam repositioning systems.
Some research in this area at Stanford is supported by Varian Medical stems.
34(2007); http://dx.doi.org/10.1118/1.2761280View Description Hide Description
Purpose: In 2004, ASTRO published a curriculum for physics education. The document described a 54‐hour course. In 2006, the committee reconvened to update the curriculum. Method and Materials: The committee is composed of physicists and physicians from various residency program teaching institutions. Simultaneously, members have associations with the AAPM, ASTRO, ARRO, ABR, and the ACR. Representatives from the latter two organizations are key to provide feedback between the examining organizations and ASTRO. The subjects are based on ACGME requirements (particles, hyperthermia), while the majority of the subjects and appropriated hours/subject was developed by consensus. Results: The new curriculum is 55 hours containing new subjects, redistribution of subjects with updates, and reorganization of core topics. For each subject learning objectives are provided and for each lecture hour, a detailed outline of material to be covered. Some changes include: a decrease in basic radiological physics; addition of informatics as a subject, increase in IMRT; and migration of some brachytherapy hours to radiopharmaceuticals. The new curriculum was by the ASTRO board in late 2006. It is hoped physicists will adopt the curriculum for structuring their didactic teaching program, and simultaneously the ABR for its written exam. The ACR uses the ASTRO curriculum for their training exam topics. In addition to the curriculum, the committee added suggested references, a glossary, and a condensed version of lectures for a PGY2 resident physics orientation. Conclusion: To ensure continued commitment to a current and relevant curriculum the subject matter will be updated again in two years' time.
34(2007); http://dx.doi.org/10.1118/1.2761281View Description Hide Description
Purpose:Graduate students, residents, and allied health professionals rely on medical physicists to help them learn about medical physics, and online learning is increasingly being used to supplement or replace traditional didactic education. Free and Open Source Software (FOSS) versions of course management and authoring software are available for creating and managing media for online courses. These software packages can be easier to use in the long run because they tend to be more standards compliant, which makes maintenance of the content more manageable. Methods and Materials: FOSS course management software was implemented to supplement a yearly physics course offered to residents. Management of the system was relatively easy, and incorporating materials from a variety of sources was relatively straightforward. Additions and updates are immediately reflected in the online course, and features in the software allow the residents to take an active role in their own education.Results: Initially, the online content mirrored the handout binder given to the new residents, and residents adapted very quickly to using the new system. Residents appreciated the almost immediate feedback provided by computer‐graded quizzes, and the course faculty were able to generate reports showing questions that were either more difficult or not covered very well in the lectures. These reports provided the basis for review sessions that were interspersed with the lectures. In the short term, it placed an increased burden on faculty to move materials online, but modifying them is currently somewhat easier. Conclusion:Learning to use FOSS tools to author and manage course materials is one way to create an enhanced learning environment, benefiting both learners and teachers. As we learn to take advantage of more of the features of the software, the learning environment can be enhanced even further and can be applied to more than just resident education.
34(2007); http://dx.doi.org/10.1118/1.2761282View Description Hide Description
Purpose: The goal of this study was to develop tools for the training of radiation therapists, radiation oncologists,medical physicists, and medicaldosimetrists in the clinical usage of CT‐based Image‐GuidedRadiation Therapy. The training application was developed in MATLAB, and will be compiled for free distribution when completed. The first version of the application will include CT‐based IGRTimaging data. Method and Materials: When the IGRT Training and Simulation application is launched, the user will be prompted to 1.) Select one of the case studies for image review, or 2.) Review Random Images. The simulator will then load the reference CTimages and the IGRTCTimages into the simulator from an IGRTdatabase of example images. When loaded, the images will not be co‐registered with each other. The user will have the option to 1.) Perform an automatic image registration, or 2.) Manually register the images. Approximately one third of the stored image registrations will contain known positional errors that were purposely inserted by the investigators. In addition to developing skills with image‐registration, the IGRT simulator also contains tutorials and training datasets that address other clinical scenarios. Results:Images have been acquired from IGRT treatments that contain common errors and/or anatomical changes that occur during the course of therapy. These images will be used in the IGRT Training and Simulation application to aid in the identification of errors, such as a new tumor being developed in a lung patient, substantial tumor regression, or rectal and bladder filling in prostate patients. Conclusion: An IGRT simulator is currently being developed for the training of radiation therapists, radiation oncologists,medical physicists and medicaldosimetrists. Results from the initial release of the application will be presented at the meeting.
34(2007); http://dx.doi.org/10.1118/1.2761283View Description Hide Description
Purpose: Justification of clinical physics staffing levels is difficult due to the ever increasing time demands to implement new technologies and by lack of direction as how to equate clinical needs with the staffing levels and competency required. When a physicist negotiates staffing requests to administration, she/he often refers to “blue book” (ACR) staffing suggestions, and resources such as the Abt studies. This approach is often met with questions as to how to fairly derive the time it takes to perform tasks properly, and what level of experience is actually required. The result is often insufficient and/or inexperienced staff handling complex and cumbersome tasks. We undertook development of a staffing justification grid to equate the clinical needs to the quantity and quality of staffing required. Method&Materials: The first step is using the Abt study, customized to the clinical setting, to derive time per task multiplied by the anticipated number of such tasks. Inclusion of vacation, meeting, and developmental time is incorporated along with allocated time for education and administration. This is followed by mapping the tasks to the level of competency/experience needed, for example in an academic setting the faculty appointment levels. Non‐staff personal, such as IMRT QA technicians or clerical staff should also be part of the equation. This grid method not only equates the clinical needs with the quantity of staffing, but also generates the personnel budget, based on the type of staff and personnel required. Results: By using the staffing justification grid, we derived strong documentation to justify a substantial budget increase. Conclusion: Though our grid is for a large academic facility, the methodology can be extended to a non‐academic setting, and to a smaller scale. The grid is easily adaptable when changes to the clinical environment change, such as an increase in IMRT or IGRT applications.
34(2007); http://dx.doi.org/10.1118/1.2761284View Description Hide Description
Purpose: This presentation will explore the strategies employed in transitioning to paperless and film‐less department; the challenges, costs, reimbursement issues and the economic value created. Methods and Materials: Differential state analysis was performed using financial, time‐motion and qualitative metrics to examine and evaluate the effects of establishing a fully electronic EMR paradigm for a major hospital‐based RT department. Several project and change management strategies were employed to gain user and clinician acceptance, and to analyze and modify workflows to adapt to the new electronic paradigm. Evaluation and selection of a robust, adaptable and full‐featured EMR, along with imaging and treatment device interfaces was done using multiple data points and clinical references. Results: Once fully implemented, significant efficiencies and increases in productivity were measurable. Time savings and increased efficiencies in chart related activities that now allowed for distributed and simultaneous data access, and distributed image review were dramatic. Further improvements were seen in scheduling, charge capture and billing related activities. Quality measures due to improved and more comprehensive treatment documentation, along with qualitative measures relating to workplace psychology all showed improvement. Conclusion: Although the challenges may seem daunting from a financial and project management perspective, the measurable benefits of a fully paperless and film‐less department demonstrate a net positive benefit. In addition, pay‐for‐quality initiatives and tightening reimbursement standards will demand a level of data richness that can only be obtained from a suitable and fully utilized EMR.
34(2007); http://dx.doi.org/10.1118/1.2761285View Description Hide Description
Purpose: To discuss radiation safety issues that may arise in the event of death of patients who have received radiopharmaceutical therapy or a radioactive implant and to educate clinical medical physicists in specific procedures performed by pathology personnel, morgue personnel, funeral directors and crematory workers that present radiation safety risks to those workers. Also to provide guidance on lessons learned by the author in communicating appropriate radiation safety procedures to funeral professionals and working with state agencies that regulate funeral homes and crematories. Method and Materials: The author researched pathology, embalming, and cremation procedures and facilities and spent considerable time on‐site in such facilities to gain an understanding of the specific risks presented to personnel and safety precautions that are currently used (or not used). Results: The author prepared instructions to be provided to personnel in the event of the death of radiopharmaceutical therapy or radioactive implant patient to comply with state and federal radiation control regulations and ensure personnel safety. The author also provided education to local funeral directors and spoke on this subject at a state funeral directors conference. Conclusions: It is not a matter of “if” but rather “when” a clinical medical physicist at a facility performing radiopharmaceutical therapy or radioactive implant procedures will receive a call regarding radiation safety procedures for a deceased patient. It is preferable to be prepared with specific instructions and establish a relationship with your pathology laboratory, morgue, and local funeral professionals in advance than to flounder when the event occurs.
34(2007); http://dx.doi.org/10.1118/1.2761286View Description Hide Description
Purpose: Although well known for its work in dosimetry, the IAEA requires experts in medical radiation physics to assist with projects in developing countries such as commissioning radiotherapy machines and treatment planning systems. Consultants are used also to draft documents and provide advice on divergent topics such as quality assurance for IMRT and PET‐CT, and a methodology for comprehensive auditing in radiotherapy.Method and Materials: Through its publications, the IAEA's attention in developing countries is focused on redressing the dual gaps in access to basic technology using radiation medicine and in advanced technology that attempts to increase the fraction of patients treated with curative intent. Results: DMRP has produced information of relevance to the practice of medical physics in any centre of limited resources irrespective of geographic location. In educating medical physicists, the handbook for teachers and students in Radiation Oncology Physics has been supplemented by a β‐version of a set of 2,500 slides to assist in self‐directed studies, recently posted on the DMRP web site for comments and feedback. A syllabus for medical physics in diagnostic radiology has been prepared and co‐authors are being recruited to write individual chapters. TRS‐430 on QA for treatment planning systems has been supplemented by two additional documents on type tests to be done by the supplier, and acceptance and commissioning tests to be done on‐site. A methodology for comprehensive auditing of radiotherapy centres and a more specific document on physics auditing in radiotherapy have been prepared. A new document describing a basic radiotherapy facility including its human resources component has completed technical editing. Conclusion: New projects and up‐coming opportunities, and the process to become an IAEA consultant will be described in the hope that AAPM members will be encouraged to offer their services to strengthen the practice of medical physics internationally.
The Great Debate: The Future of IGRT is…
TU‐D‐M100J‐01: The Great Debate: The Future of IGRT Is…Megavolt CT…Kilovoltage CT…Ultrasound‐Based Hybrids…MRI Guidance…3D Deformable Image Registration34(2007); http://dx.doi.org/10.1118/1.2761378View Description Hide Description
Introduction:Image‐guided radiation therapy (IGRT) promises to reduce or eliminate conventional limitations posed by geometric uncertainty, opening the way for dose escalation, margin reduction, innovative treatment techniques, hypofractionation, patient‐specific protocols, reduced normal tissue toxicity, and increased tumor control. This symposium presents a debate regarding the numerous technologies brought to bear in IGRT, including image — and information‐based technologies for therapy guidance. Topics and Speakers: The symposium features five distinguished speakers. Dr. J. Pouliot will present on the topic of megavoltage (MV) CT and cone‐beam CT(CBCT), reviewing the advances and advantages associated with imaging the patient in the treatment position with the therapy beam itself. Dr. J.‐J. Sonke will present the case for kilovoltage (kV) CBCT, discussing the latest advances in CBCT technology, image quality and accuracy, and protocols for offline, adaptive, and online 3D and 4D guidance. In light of the radiation risk posed by such modalities, Dr. W. Tome will present a strategy that hybridizes MV or kV CBCT (obtained at weekly intervals) with 3D ultrasound (obtained for daily guidance), wherein a (weekly) gold‐standard 3D ultrasoundimage provides close correspondence to CBCT. In this way, conventional uncertainties in ultrasound‐based alignment are minimized, and accurate daily ultrasound guidance is achieved with a ∼80% reduction in cumulative dose to the patient. Dr. J. Lagendijk will offer an innovative approach in which the treatment machine is fully integrated with magnetic resonance imaging (MRI), allowing precise soft‐tissue visualization for online guidance, verification, monitoring, and biological optimization. The technological challenges and advances in such development are described, including potential applications in treatment of the prostate, cervix, liver, and lung. Finally, Dr. K. Brock will argue that the future of IGRT lies not within a given imaging modality, but in the use of multiple structural and functional modalities geometrically resolved by means of deformable modeling. By combining diagnostic quality images with daily IGRT, accurate tumor targeting can be achieved in a manner that accounts not only for daily setup error but also morphological deformation and physiological change over the course of treatment.Format: The debate will consist of three rounds: 1.) a summary / overview of each IGRT approach; 2.) presentation, debate, and rebuttal regarding the role of each approach in the future of IGRT; and 3.) open format question and answer from the panel and audience. Time and technology permitting, a winner will be informally determined by feedback from the audience.
Functional Imaging for Radiotherapy Guidance
34(2007); http://dx.doi.org/10.1118/1.2761590View Description Hide Description
34(2007); http://dx.doi.org/10.1118/1.2761591View Description Hide Description
Delivery of radiotherapy through hypoperfused pulmonary regions for lungcancer treatment has been shown to result in less pulmonary injury in a single prospective trial. This finding suggests a strategy for image‐guidedradiotherapy utilizing physiological images in radiotherapytreatment planning for image guidance to avoid the irradiation of highly functional regions and minimize the injury and/or function loss following thoracic radiotherapy. Patients may have inhomogeneous lung function distribution due to tumor invasion of the airway and vascular structures and/or preexisting pulmonary diseases. Imaging studies have found the prevalence of these hypoperfused regions adjacent to the primary tumor from 43 to 74% in non‐small cell lungcancer cases. However, the current thoracic treatment planning practice has been primarily based on using anatomical information from the treatment planningcomputed tomography(CT). Therefore, the non‐uniform distribution of regional function of normal lungtissue has not been considered in the process of treatment planning.Imaging modalities that have been reported in treatment planning studies to provide image guidance to identify the highly functional regions include single photon emission computed tomography perfusion, hyperpolarized gas magnetic resonance ventilation, and 4D CT derived ventilation imaging. No prospective studies demonstrating improvement in outcome using these modalities for functional image‐guidedradiotherapy have yet been reported. Strategies to incorporate functional image guidance include identification of highly functional regions by an expert for avoidance, automated segmentation of pulmonary regions with the highest function for avoidance, and optimization of functional metrics including the dose function histogram.
This lecture will provide an overview of the physiologic origins of the functional imaging methods, post‐acquisition processing, and strategies to integrated functional imaging into thoracic treatment planning.
1. Understand clinical basis for the use of functional imaging for treatment planning.
2. Survey the functional imaging modalities which may be utilized for image‐guidance.
3. Review strategies to integrated functional imaging into thoracic treatment planning.
34(2007); http://dx.doi.org/10.1118/1.2761592View Description Hide Description
PET/CT simulation of tumors in the thorax suffers from potential misalignment between the CT and the PETimages even though the data are acquired in the same imaging session on the PET/CT scanner. The misalignment was caused by the fast acquisition of the CTimages in sub‐second temporal resolution and the slow acquisition of the PET data of over several minutes. Current approach of degrading the CTimages in spatial resolution does not fix the problem. We will go over the pitfalls resulted from the mismatch of CT and the PET data, and will review a new average CT scan to mitigate this problem, and its potential impact to radiation therapy planning.