Volume 35, Issue 6, June 2008
Index of content:
- Joint Imaging/Therapy Symposium: Room 351
- MRI in Radiation Therapy: From Simulation to Online Image‐Guidance
35(2008); http://dx.doi.org/10.1118/1.2962397View Description Hide Description
CT‐simulation has become essential in the planning of external beam radiotherapy for prostate cancer. The 3D‐localization of the prostate has reduced setup uncertainty and permitted the use of smaller margins. The trade‐off is increased interobserver differences, particularly in contouring the apex of the prostate. MRI much more clearly delineates the borders of the prostate, especially the prostate‐bladder interface, prostate‐rectal interface and apex. MRI also provides greater resolution of tumor location and extent, although MRI‐simulation is typically accomplished using a body coil, which has lower resolution as compared to an endorectal coil. Of note, MRI prostate volumes are consistently less than that from CT. One pitfall of MRI‐simulation is that commercial planning systems are CT‐based. Heterogeneity corrections incorporate CT‐based Hounsfield units. Moreover, if fiducial markers or Calypso beacons are outlined on CT, it is best to demarcate the CTVs from the same image set, namely CT, using MRI as a reference. Accurate fusion of CT and MRI is essential in this process. If the fusion is based solely on bony anatomy, the prostate may be in a different position on MRI. The potential errors are magnified if the fiducials are outlined on CT and the anatomy defined on MRI, and the fusion is not based on soft tissue. A rationale for and the potential benefits of functional imaging (MR‐spectroscopy and dynamic contrast enhanced MR) to define the dominant tumor prostatic lesion will be described.
35(2008); http://dx.doi.org/10.1118/1.2962398View Description Hide Description
Magnetic resonance(MR)imaging has advanced to offer high intrinsic contrasts, biologically‐relevant signals, rapid volumetric imaging, and compatibility with intervention. These advances are strikingly compatible with the current efforts in advancing the precision and accuracy of radiation therapy. The growing drive towards conformal, biologically targeted RT will draw MRimaging data and MR technology into radiationoncology practice. Simulation and planning in RT now routinely draws on MR for target and normal tissue segmentation. This includes the growing trend toward installing dedicated MR systems in the radiationoncology department. Furthermore, there have been numerous reports on the development of integrated MR‐guided RT units for increased precision and accuracy in RT. The rationale for these developments and the technical challenges associated with successful execution will be discussed.
35(2008); http://dx.doi.org/10.1118/1.2962399View Description Hide Description
In vivo functional magnetic resonance imaging is becoming an increasingly important tool for assessment of therapeutic response and normal tissue toxicity. Early assessment and prediction of treatment response and potential risk for toxicity allow for individualized re‐optimization of therapy, which represents a novel concept and a paradigm shift from conventional clinical trials. Potential benefits and risks for therapy should be an integral part of clinical decision making. Organ perfusion, vascular permeability, tissue and tumor metabolism, and cellular structures can be assessed by functional and metabolic MRimaging. Recent studies have shown that functional and metabolic MRimaging can provide an indication of therapeutic response of tumor, and possibly do so prior to the radiographic changes. Also, potential organ and tissue toxicity can be assessed during and after therapy using the same imaging techniques, and possibly predicted prior to clinical symptoms. This presentation will provide an updated overview on functional and metabolic MRimaging in clinical trials for assessment of treatment response.
1. Overview potential values of functional and metabolic MRimaging in phase I/II trials for assessment of therapeutic responses and normal tissue toxicity.
2. Discuss the advantages and limitations of using in vivo functional and metabolic MRimaging in clinical trials compared to conventional paradigms.
- Image‐Guided Therapy: From Fundamentals to New Frontiers
35(2008); http://dx.doi.org/10.1118/1.2962591View Description Hide Description
Concurrent advances in medical imaging,therapeutics, and understanding the biological basis of disease progression and treatment response point convincingly to a transformative approach to medical interventions in the decades ahead. Such interventions are marked by a dramatic increase in the utilization of image information from multiple modalities and demand accurate coregistration of structural and functional information across a broad range of spatial and temporal scales. The scope of advanced therapeutic approaches enabled by such advances is broad, ranging from high‐precision image‐guidedradiation therapy and surgery to minimally invasive target ablation, cell‐based therapies, and other forms of novel therapeutics. Moreover, the information acquired during the course of information will drive patterns of therapy delivery that are increasingly adaptive and patient‐specific. This symposium focuses on the scientific principles of imaging, guidance, treatmentdelivery, and feedback / adaptation in the context of advanced medical interventions and looks ahead to new technologies being developed for novel image‐guided therapies. Four expert speakers have been invited to present on topics central to such advancement: Dr. Siewerdsen will discuss principles of imaging performance, imaging task, and new imaging technologies; Dr. West will address principles of geometry, registration, and uncertainty (e.g., target registration error) in relation to real‐time tracking and navigation; Dr. Sherar will discuss a broad spectrum of technologies for therapeuticdelivery, including physical, molecular, chemical, and cellular means by which a therapeutic insult can be delivered to disease under image guidance; finally, Dr. Yan will describe principles of feedback and control in the development of adapative therapies. Together, these topics present a “closed‐loop” in issues of imaging, navigation, therapy delivery, and adaptation that are central to the advancement of image‐guided interventions.
- Image Processing and Analysis for Radiotherapy Guidance
35(2008); http://dx.doi.org/10.1118/1.2962789View Description Hide Description
4D CT is routinely used in radiation therapy planning of moving targets. Its current role is commonly limited to assessing the extent of target motion, and designing an aperture that encompasses this motion. However, much more information can be extracted from 4D imaging, if computational and visualization tools were available. Examples include: 1) regional ventilation analysis in lung irradiation; 2) analysis of serial 4D CT to quantify tumor trajectory variations 3) identification of corresponding airway bifurcations to provide validation of deformable registration algorithms 4) interactive 4D volume rendering to permit visualization of structures within the radiation field. While the core tools of image processing remain the same (segmentation, image registration, change detection, visualization), extrapolation to 4D requires new and powerful implementations.
35(2008); http://dx.doi.org/10.1118/1.2962790View Description Hide Description
The accelerating introduction of molecular imaging into medicine holds promise for cures of numerous intractable diseases. In vivomeasurements of pathologic details at the molecular level are on the horizon but substantial work on improved precision and accuracy are necessary before methods can be clinically useful. Accurate knowledge of spatial and temporal dimensions of molecular measures is necessary before such measures can be validated as biomarkers of clinically significant endpoints. These are functions that AAPM members have performed over and over again in medicine over the five decade history of the association. The extension into molecular imaging, however, requires even broader participation in multi‐disciplinary teams extending beyond traditional departmental boundaries of radiology and radiation oncology. This presentation reviews developments in molecular imaging and the growing need to fuse molecular events to the spatial framework of well known anatomical imaging methods. The process of translation requires participation in preclinical studies using animal models to validate methods in experimentally controllable environments. The AAPM can play an important role in this process at numerous levels. Members can participate in the design and testing of new instrumentation for both preclinical/animal and human uses. Members can also use well documented society methods for developing nationally acceptable imaging standards and procedures for assuring the quality of data. This is especially important when data is intended for the use of regulatory agencies such as the FDA to prove the safety and efficacy of new methods of medical care.
1. Understanding the meaning of “molecular imaging”
2. Understanding the process for fusing molecular imaging into clinical medicine.
3. Understand the potential role for medical physics in applying molecular imaging.
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35(2008); http://dx.doi.org/10.1118/1.2962792View Description Hide Description
Ongoing developments in multimodality and 4D imaging technologies are providing opportunities to improve tumor localization and patient modeling for treatment planning and to reduce setup variations and margins for treatment delivery. Proper use of these technologies can provide greater sparing of dose to normal tissues and permit safer escalation of tumor doses. Imaging techniques are also being developed to help predict response to treatment during therapy when interventions and adaptations are still possible. The explosive growth in imaging technology has been followed by growth of technologies to manage the plethora of data now being generated.
One key technology is image registration, which can be thought of as producing the “glue” to allow quantitative integration of anatomic, functional and dosimetric information from different imaging studies. Indeed, most modern imaging workstations, treatment planning systems and even treatment delivery systems now provide tools for image registration and data integration. These tools range in sophistication from simple manual registration involving just a few degrees of freedom (DOF) to fully automated registration techniques which produce deformation fields at the resolution of the image data.
Unfortunately, widespread use of these techniques for all but simple situations has been impeded by lack of more realistic models which can accommodate processes other than just deformations such as tissue loss, gain, and sliding. The situation is also complicated by the realization that the optimal number of DOF and other registration parameters vary from tissue to tissue; using too few or too many DOF or inappropriate parameters can cause inaccurate or unphysical results. Fortunately, developments aimed at overcoming these obstacles continue to emerge and will pave the way to broader clinical use of image registration. These developments as well some of the remaining hurdles will be discussed.