AJR: True whole-body PET/CT changes management in cancer patients

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Adopting a true whole-body 18F-FDG PET/CT field of view in the imaging of cancer patients could lead to more accurate staging and restaging than achieved with the routinely used limited whole-body field of view, according to a study in the December issue of the American Journal of Roentgenology (AJR).

“Use of the routine field of view for whole-body FDG PET/CT can lead to underestimation of the true extent of the disease because metastasis outside the typical base of skull to upper thigh field of view can be missed,” said the study's lead author Medhat M. Osman, MD, PhD, associate professor and the director of the division of nuclear medicine and PET/CT at Saint Louis University in St. Louis.

The study included 500 patients who underwent true whole-body FDG PET/CT, from the top of the skull to the bottom of the feet. Fifty-nine of 500 patients had PET/CT findings suggestive of malignancy outside the limited whole-body field of view. New cancerous involvement was confirmed in 20 of those patients. Thirty-one of those patients had known or suspected malignancy outside the limited whole-body field of view at the time of the true whole body study. Among the other 28 patients, follow-up data were not available for two, six had false-positive findings, and new cancerous involvement was confirmed in 20, according to Osman and colleagues.

The presence of previously unidentified malignant sites outside the typical limited whole-body field of view was confirmed in four percent of the 500 patients. “Detection of malignancy outside the limited whole-body field of view resulted in a change in management in 65 percent and in staging in 55 percent of the 20 cases,” said Osman.

Adopting the true rather than limited whole body field of view in PET/CT of cancer patients required adjustments in the daily clinic schedule because scanning time increased 30 to 40 percent. However, the time saved from using CT for attenuation correction in PET/CT can be partially invested in performing true whole-body PET/CT, according to Osman and colleagues.

Finally, with advances in both hardware and software technology of newer PET/CT scanners, the time required for true whole-body image acquisition will continue to decrease, and the coaxial scan range will continue to expand, predicts Osman and colleagues. “For example, we are using a PET/64-MDCT scanner with time-of-flight technology and lutetium-yttrium oxyorthosilicate crystals that enables true whole-body acquisition in 20 minutes in patients with a normal body mass index. With that scanner we can use a one minute per bed position, as opposed to the three minutes per bed position used in this study, and patient comfort and scanner throughput can be maintained,” wrote Osman and colleagues.

Furthermore, although the FDG dose was kept constant, the patients were exposed to a slightly higher radiation dose owing to the inclusion of additional portions of the body in the low-dose unenhanced CT portion of the examination, added the authors.

“Our results show that compared with limited whole-body acquisition, use of true whole-body image acquisition may increase the accuracy of staging, change the treatment of cancer patients, and help in the selection of more accessible biopsy sites, avoiding unnecessary invasive surgical procedures and eliminating unnecessary imaging and its additional cost in time and money,” concluded Osman and colleagues.