The value of PET/CT is being over‐sold as a clinical tool in radiation oncology
2005; Wiley; Volume: 32; Issue: 6Part1 Linguagem: Inglês
10.1118/1.1924458
ISSN2473-4209
AutoresLei Xing, Barry W. Wessels, William R. Hendee,
Tópico(s)Advanced Radiotherapy Techniques
ResumoMedical PhysicsVolume 32, Issue 6Part1 p. 1457-1459 Point/counterpointFree Access The value of PET/CT is being over-sold as a clinical tool in radiation oncology Lei Xing, Lei Xing Stanford University School of Medicine, Department of Radiation Oncology, Stanford, California 94305-5847 (Tel: 650/498-7896, E-mail: lei@reyes.stanford.edu)Search for more papers by this authorBarry Wessels, Barry Wessels University Hospitals - Case Western Reserve University, Department of Radiation Oncology, Cleveland, Ohio 44106 (Tel: 216/844-2519, E-mail: Barry.Wessels@uhhs.com)Search for more papers by this authorWilliam R. Hendee, William R. Hendee ModeratorSearch for more papers by this author Lei Xing, Lei Xing Stanford University School of Medicine, Department of Radiation Oncology, Stanford, California 94305-5847 (Tel: 650/498-7896, E-mail: lei@reyes.stanford.edu)Search for more papers by this authorBarry Wessels, Barry Wessels University Hospitals - Case Western Reserve University, Department of Radiation Oncology, Cleveland, Ohio 44106 (Tel: 216/844-2519, E-mail: Barry.Wessels@uhhs.com)Search for more papers by this authorWilliam R. Hendee, William R. Hendee ModeratorSearch for more papers by this author First published: 11 May 2005 https://doi.org/10.1118/1.1924458Citations: 14AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat OVERVIEW PET and CT are important imaging technologies in the diagnosis and staging of cancer and in monitoring and evaluating the effectiveness of treatment. Combined PET/CT units are being marketed as advantageous because they offer a common platform for the technologies so that patient convenience is improved and misregistration of information is reduced. Some physicists agree with this marketing message, while others believe that PET/CT is a technology that adds to healthcare costs without contributing substantive value. This controversy is the subject of this month's Point/Counterpoint. Arguing for the Proposition is Lei Xing, Ph.D. Dr. Xing earned his Ph.D. in physics from the Johns Hopkins University and obtained his medical physics training from the University of Chicago. He is currently an Associate Professor of Radiation Oncology at Stanford University. His major areas of interest are intensity modulated radiation therapy (IMRT), image-guided radiation therapy (IGRT), PET/CT and other emerging molecular imaging modalities, such as MR spectroscopic imaging (MRSI) and fluorescence/bioluminescent imaging, and their integration with radiation therapy treatment planning systems. He has served on the AAPM IMRT Subcommittee, and the Medical Physics Editorial Board. He is certified by the American Board of Radiology. Arguing against the Proposition is Barry Wessels, Ph.D. Dr. Wessels is currently Professor and Director, Division of Medical Physics and Dosimetry at Case Western Reserve University. He received his Ph.D. in nuclear physics from the University of Notre Dame in 1975. For the next two decades, Dr. Wessels served as a group leader at the MIT reactor laboratory and as a faculty member at The George Washington University. His areas of specialty include the dosimetry and radiobiology of radionuclide therapy, image fusion and clinical trial design. Dr. Wessels is currently a member of the MIRD and REIR committees of the SNM and has served as President of the American Board of Sciences in Nuclear Medicine (ABSNM), Chair of the AAPM Task Group on Radiolabeled Antibody Dosimetry, RTOG committee on physics and the ICRU Nuclear Medicine Advisory Committee. He has published over 200 peer-reviewed journal articles, book chapters, proceeding papers and abstracts. FOR THE PROPOSITION: Lei Xing, Ph.D. Opening statement Hybrid PET/CT scanners1 are advertised as cutting-edge technology. Many clinics are making purchasing decisions through the influence of advertisements and the pressure of competitors. Since 2000, more than 300 PET/CT units have been purchased, even though the clinical benefits of the technology have not been unequivocally demonstrated. At this point, the “hopes” for PET/CT greatly outweigh the “facts” about the merit of PET/CT. Subjective impressions have been the dominant factor influencing PET/CT purchase decisions.2,3 Hybrid PET/CT systems have several positive features that are absent with stand-alone PET and CT units. PET/CT is a hardware-based image-fusion technology that virtually eliminates the uncertainty and inconvenience of software fusion of separate PET and CT images that are acquired with patients in different positions. However, PET images alone often contain enough information to answer clinically-important metabolic questions3 without superposition of CT images. For treatment planning in radiation therapy, the use of CT/PET fiducials and software fusion has provided sub-centimeter spatial resolution4,5 and yielded excellent clinical results.6 Currently available fusion software performs well in the head and neck, and less well in the thorax, abdomen and pelvis because of positioning difficulties and involuntary motion. However, reasonable results can usually be acquired in these regions by use of PET transmission scans and close collaboration of PET and CT technologists. Image co-registration is sometimes a problem also with PET/CT in these regions, because the images are acquired sequentially rather than simultaneously.7 Software fusion requires multiple steps and is tedious, but these problems will ultimately be resolved through research. The bottom line is that hardware-based fusion is not the ultimate solution for image co-registration, and a hybrid machine is not needed for every combination of imaging technologies that can conceivably yield useful fusion images. For example, a hybrid PET/MRI unit hardly seems necessary, even though some researchers are considering it. It is indisputable that CT measurements for PET attenuation corrections greatly reduces PET scan time—but it also ties up the CT scanner and increases the radiation dose to the patient. A hybrid PET/CT unit is not a “must-have” clinical tool in radiation oncology, and does not automatically elevate an oncology service to “world-class” status. Conversely, an institution can be “world-class” without a hybrid PET/CT unit.9 Software fusion, including rigid and deformable image registration, has several virtues and should be targeted for further research. Further, the possible clinical benefits of hybrid PET/CT should be carefully documented by investigators. At the end of the day, the usefulness of any technology is justified only through definitive diagnostic and therapeutic gains. Rebuttal Dr. Wessels puts his faith in marketplace trends, and bets that the marketplace cannot be very wrong. That is exactly what concerns me. I caution that, historically, the marketplace can indeed be wrong, and even badly wrong. If one is not convinced, perhaps revisiting the competition between beta and VHS file formats as a video standard in the 1970s will help. That said, I do not totally disagree with Dr. Wessels’ argument, but would like to challenge him further by asking: “Can the marketplace be that right?” The marketplace is an interesting arena to watch but should never be a metric for technology assessment. Most likely, the truth of the debate about the value of PET/CT lies somewhere between our respective Point/Counterpoint positions. Clinical and scientific data are needed to objectively determine where PET/CT is located on the coordinate starting from “totally wrong” to “absolutely right,” whether the clinical benefit of PET/CT is sufficient to offset its higher capital and running costs, and whether the alternative software fusion is an option. Dr. Wessels also mentions that the hybrid PET/CT facilitates clinical operation. While the hybrid system is probably not a fundamental breakthrough that changes the paradigm of medical imaging, it does provide a more convenient solution for radiation oncology practitioners compared with the currently available software approach for fusion of PET and CT images. In an era where time, convenience, and efficiency are money, this value should certainly not be underappreciated. On the other hand, we should acknowledge that this benefit does not come for free; there are a number of practical issues associated with it.3 Aside from the capital and operational costs, increased radiation dose, changes in medical/administrative procedures, appropriate selection of patients, etc., should all be considered. One should also note that difficulties with current fusion software may be short-lived and things may improve in the near future. The fact sheet for the hybrid PET/CT is multi-dimensional. It is still too early to claim that PET/CT is a technology for everyone, and that the application of PET/CT should not in any circumstance be dictated by reimbursement. It is my view that if multi-modality imaging (not just PET, but also other related modalities) is to have a genuine impact in radiation oncology, a versatile, low cost, and long-term solution other than hardware fusion has to be in place. AGAINST THE PROPOSITION: Barry Wessels, Ph.D. Opening statement Many spirited discussions occur within one or more of the following scenarios: 1) one discussant is talking apples and the other oranges, 2) both positions have overlapping truth sets, and 3) the definitive experiments have not been performed. Such is the case with the present “value” discussion on the net worth of integrated PET/CT for radiation oncology. The fact that a New England Journal of Medicine article in 2003 by Lardinois et al.,8 and a Special Supplement in the January 2004 issue of The Journal of Nuclear Medicine, were devoted entirely to integrated PET/CT (Ref. 9) suggests that something major is afoot. Proponents of the proliferation of PET/CT machines would argue that the technology already has had a profound impact on the restaging of disease and for radiation therapy treatment using expanded or contracted target volumes for disease located in the head, neck, thorax and abdomen.10 The apples and oranges aspect of this argument may be largely due to the simple addition of functional information to the anatomical imaging process alone and may not have anything to do with the method of acquisition. This addition can be accomplished by any one of three image registration methods (visual side-by-side, software, and hardware fusion). The latter of these methods is currently accomplished by the use of relatively costly PET/CT units. Clearly, the definitive experiments have not been completed to resolve the argument over the value of PET/CT. Most studies compare “horse-and-buggy” visual side-by-side fusion with inherently coregistered PET/CT scans, and do not give relatively inexpensive, independent image fusion software packages an even technical match.11 A common truth set for all applications is 1) the need for a reliable automatic image segmentation algorithm for PET to draw corrected target volumes;12 2) the requirement for machine-based fiducial alignment and patient immobilization systems;13 and 3) respiratory gating for all.14 One might argue that this truth set is correct, but PET/CT may be the wrong combination of machines. The pundits may have a point here; PET/MR is probably not far around the corner.15 But at the end of the day from one who is constantly confronted with patient alignment, fusion, throughput and convenience concerns, the integrated PET/CT scanner has a unique advantage to potentially solve all of these problems in a single patient visit. The cost in physician, physicist, radiation oncology and nuclear medicine staff time needed for multiple imaging sessions that usually require redundant immobilization equipment in separate departments is just part of the challenge of a nonintegrated PET/CT approach to image fusion. The expanded utility of PET/CT for radiation therapy is driven not just by expert technocrats who have a vested interest in its proliferation. It is also being demanded by referring physicians during combined tumor board case presentations, and ultimately will be expected by patients. Is this not in the same class as the unproven “value added” benefit purported by IMRT treatment for patients in radiation oncology? To this end, can the marketplace be that wrong? Rebuttal Virtually all the “facts” stated by both my worthy opponent and me are in substantial agreement regarding this discussion topic. It is heartening that most of the cited literature is shared common ground. However, there is little agreement in the valuation of the cost/benefit ratio for both the investigator and the patient concerning this new technological combination. My colleague states that “software fusion requires multiple steps and is tedious” (agreed!), “but these problems will ultimately be resolved through research.” However, improvements to the software fusion process may only add to the tedium with limited returns on effort. This problem can be generalized to all image-guided therapy modalities, namely the functional definition of “real-time.” To properly gate for organ motion and provide reproducible patient positioning necessary for accurate therapy, “real time” will be most likely defined in units of milliseconds. Using this metric, both software fusion and PET/CT fail miserably. Typically for software fusion, “real-time” is on the order of several hours to days for the acquisition of separate PET and CT scans taken in the treatment position. For state-of-the-art PET/CT imaging using an attenuation map acquired from CT, “real-time” is still fractions of an hour. The potential for patient movement, misalignment and multiple organ motion remains problematic for both methodologies. It is reasonable to hypothesize that the “real-time” motion problem will be substantially reduced by the modality that acquires data over a window of time that is an order of magnitude closer to the motion-stopping, millisecond goal. Presently, there is a growing library where software fusion just gets it wrong for patients scanned in different positions using PET or CT originating from separate devices, and where there is no hope for organ-motion gating. Performed by skilled clinical staff, the single appointment PET/CT is the most practical solution to obtain the desired data from a single machine for patients scanned in a predetermined therapy position. REFERENCES 1D. W. Townsend, J. P. Carney, J. T. Yap, and N. C. 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