|
Main indications for PET/CT
There are numerous reports which outline the appropriate indications for FDG PET for pretreatment, post-treatment and follow-up in the study of a variety of cancers 1, 2. There are, however, no precise indications for the use of PET/CT, since the literature available is relatively limited and refers for the most part to a small number of cases. Nonetheless the literature clearly identifies that PET/CT presents important advantages with respect to PET alone in localizing and interpreting hypermetabolic lesions, especially when they are in anatomically complex body regions and in all cases where normal anatomy has been altered following surgery or radiation therapy 18, 19. A higher sensitivity and specificity of PET-CT compared with PET alone has been documented in demonstrating recovery from colorectal cancer 20, 21, ovarian cancer 22 and non-small-cell lung cancer. Studies comparing PET and PET-CT have shown that PET-CT is capable of providing additional information regarding pretreatment staging of patients with non-small-cell lung cancer, with an improvement in diagnostic accuracy particularly regarding the assessment of the N and M parameters 23, 24, 25. With regard to esophageal cancer PET and PET-CT 22, 26 have proven useful in preoperative staging, with a diagnostic accuracy greater than CT in identifying lymph node involvement . The treatment of esophageal cancer, head-neck cancer and rectal cancer often involves neoadjuvant chemoradiotherapy before possible surgery, especially when at diagnosis the cancer presents local-regional diffusion. PET and especially PET/CT 27 are able to assess the extent of treatment response with greater precision, with important consequences for treatment choice and patient prognosis. PET/CT has excellent possibilities in providing more useful information than CT with regard to performing radical radiotherapy, both for modifying treatment in the case of identifying lesions not encountered with conventional imaging techniques and for optimizing treatment plans. In modern conformation radiotherapy the precise definition of the fibrous or necrotic component of the tumor allows for appropriate corrections of the volume to be irradiated 28. With reference to the data published in the literature the PET/CT study is most appropriate in the following situations:
- staging of tumors situated in anatomically complex body regions (head-neck, mediastinum, pelvic cavity);
- staging of tumors where assessing possible lymph node involvement is particularly important, such as in non-small cell lung cancer in the pretreatment phase or ovarian cancer or colon-rectal cancer where relapse is suspected;
- assessing doubtful and inconclusive CT findings regarding relapse;
- tumors with indications for radical radiotherapy, with the aim of staging and optimizing the treatment plan.
As well as these indications, which may lead to preferential planning for the use of a PET/CT study, unforeseen cases may arise where there is difficulty in localizing and interpreting hypermetabolic lesions. These considerations underline the problem of choice a PET centre equipped with only one scanner must currently face: a centre with two or more scanners, including a PET/CT scanner, may perform several patient beds with the PET/CT scanner at the level where there are interpretative problems regarding the localization of hypermetabolic lesions. A PET centre with a single scanner, which is the most frequent situation, should look to acquiring a PET/CT scanner, which offers clear advantages for the study of numerous tumors and which compensates the greater financial investment with an increase in productivity of 25-30%. Further support for this affirmation is provided by several indications still under study which necessarily require the use of a PET/CT scanner, such as studies with 18F- FDG of multiple myeloma and with 11C-choline of prostate cancer 2.
|
|
