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Development prospects for PET/CT
The availability of PET-CT scanners opens up development prospects of metabolic imaging which although yet tobe defined are potentially highly relevant, with the possibility not only of increasing diagnostic accuracy of many indications already recognized as appropriate, but also in tackling problems of diagnostic precision and tumor staging, the study of which has so far proven difficult with PET scanners alone. The new indications, which still require studies on a sufficiently large number of cases in order to define their appropriateness, include the use of PET/CT with 11C-choline in the study of prostate cancer having already undergone treatment and suspected of relapse where conventional imaging findings are dubious or inconclusive 2. PET/CT can identify bone metastases, even small occurrences in the initial phase, as well as lymph node involvement, even when they are not enlarged, in correspondence with the pelvic cavity or the lumboaortic region. Progress has been made in multiple myeloma regarding treatment possibilities, with an improvement in cure rates or long-term survival. Owing to its ability to study the whole body and precisely locate lesions, PET/CT is able to provide more information than conventional imaging techniques not only in the pretreatment phase, but also post-treatment and in follow-up. PET/CT is able to identify a greater number of bone lesions than conventional radiography examinations, assess whether the bone lesions are in a state of activity and also demonstrate the presence or not of extra-osseous lesions 29. The PET/CT study which includes all the bone segments is capable of identifying additional lesions and completing the information provided by MR, which in general is limited to the spine and pelvis. Lastly, PET/CT has been recognized as an important technique in the study of plasmacytosis owing to its ability to identify lesion sites other than the one already known. PET/CT is particularly useful in the study of some cancers in the advanced stage or not susceptible to surgery, such as head-neck cancer, esophageal cancer, non-small-cell lung cancer and breast cancer 23. In these cases neoadjuvant chemoradiotherapy is performed, for which a pre and post-treatment assessment is vital for establishing the metabolic response to therapy. The PET/CT study precedes or at any rate is more sensitive than the simple morphological assessment 30. The availability of different chemotherapy protocols with different levels of toxicity has emphasized the need for an early assessment of patient response to treatment so as to avoid useless iatrogenic effects affecting non-responsive patients. With its greater accuracy than PET alone, PET/CT can perform a precise and early assessment even of the quantitative type regarding the response to chemotherapy at the level of the individual lesions, especially of malignant lymphomas and breast, ovarian and colon-rectal cancer 23, 24. In the study of head-neck cancer PET/CT is able to make an early assessment of the effectiveness of radiotherapy, preferably using in this case methionine labeled with 11C, for which unlike for 18F-FDG there is no uptake by inflammatory foci. PET/CT with 11C-methionine is also capable of performing a more precise assessment of residual or relapse cerebral glioblastomas following surgery or radiotherapy. Although still not fully defined, the use of PET/CT is promising in providing additional useful information for optimizing treatment management in modern conformation radiotherapy, both in its ability to reveal lesion not identified with conventional techniques, which can lead to a modification of either treatment or the size of the fields to be irradiated, and in its precise definition of the fibrous or necrotic component of the tumor, which may lead to the administration of additional dose on well defined areas, thus saving healthy tissue 2.
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