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J Thorac Cardiovasc Surg 2006;132:214-215
© 2006 The American Association for Thoracic Surgery
Letter to the Editor |
a Department of Radiology, UNC School of Medicine, CB 7510, Chapel Hill, NC 27599-7510
b Department of Surgery, Yale University School of Medicine, New Haven, Conn
(Email: khandani{at}med.unc.edu).
We read with interest the publication by Port and colleagues.
1
In fact, there is little information in the literature on the role of positron emission tomography (PET) in assessing lung lesions of this size range for malignancy, and well-defined studies are needed. However, the current publication has several shortcomings.
Most importantly, standard uptake value (SUV) should not have been used to assess the lung lesions for malignancy. SUV is a semiquantitative measure of the tracer uptake in the region of interest, which normalizes the lesion activity to the injected dose and body weight; SUV does not have a unit. Despite initial enthusiasm, it is generally accepted that SUV should not be used to differentiate malignant from benign processes and that the visual interpretation of PET studies by an experienced reader provides the highest accuracy in diagnosing malignancy.
2-5
There are many factors influencing the calculation of SUV, such as the body weight and composition, the time between tracer injection and image acquisition, the spatial resolution of the PET scanner, and the image reconstruction algorithm. The clinical role of SUV in therapy monitoring and as a measure of tumor aggressiveness is currently under investigation.
Furthermore, the intensity of malignant lesions on PET is influenced by the location in the body. During PET acquisition, which takes several minutes, lung lesions move up and down, and their effective acquisition time is reduced. Therefore the fluorodeoxyglucose avidity of small lung lesions is often underestimated. Consequently, it is justified to use a "sensitive reading" and consider tumors of mild intensity to be malignant, although this likely reduces the specificity. Additionally, the non–attenuation-corrected (NAC) images should be reviewed while dealing with small lung lesions. Considering the mildly intense appearance of small malignant lung lesions on PET, it is reasonable to use the NAC images and compare the tumor uptake with the surrounding normal lung tissue and not with the mediastinal blood pool activity, as is the case while reading the attenuation-corrected (AC) images. Although large and markedly intense malignant foci would likely be recognized on both NAC and AC images, this might not be the case for small foci. Also, the pathophysiologic basis of fluorodeoxyglucose PET rests on increased expression of Glut, upregulation of hexokinase activity, and downregulation of glucose-6-phosphatase activity in the cancer cells compared with the normal cells of the same organ, the lung in this case.
In our experience PET can be very helpful in detecting malignancy in lung lesions measuring 6 to 10 mm, provided the images are read with attention to the issues mentioned (NAC images, sensitive reading, and avoidance of SUV thresholds). Sensitivity and specificity of PET for detecting malignancy in small lung lesions (6-10 mm) is currently being evaluated by us in an ongoing prospective study.
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