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Solitary Pulmonary Nodule—bronchogenic carcinoma    

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 Whole Body Oncologic PET

By far the most common usage of PET worldwide, whole body PET can more accurately identify malignancy, stage, restage, and closely monitor response to therapy than conventional imaging alone. There are a number of reasons for this but consider one: the anatomic based modalities of CT and MR generally use "size criteria" to determine if a regional or distant lymph node contains metastatic tumor. If a lymph node is less than or equal to one centimeter, it is considered "benign," and if greater than a centimeter, "malignant." However, this is really an educated guess based on statistical data and of course one can have early metastases in a tiny lymph node, and conversely an enlarged lymph node can be reactive and benign. By measuring the metabolic activity of the lymph node directly, PET can more accurately predict tumor involvement.

Below is a list of current CMS (Medicare) approved indications for whole body oncologic PET. The list does contain most of the common tumors. PET is typically used in staging and restaging (after completion of a course of therapy) cancer. Usually, a tissue diagnosis is achieved prior to PET imaging but occasionally, PET can assist in actual diagnosis where one of these tumor types is strongly suspected but the primary lesion cannot be located (e.g. suspected Head & Neck cancer with cervical metastases) or to help guide biopsy into the "malignant" portion of the tumor (as opposed to the adjacent reactive tissue). PET can also be used for diagnosis of possible malignancy in a solitary pulmonary nodule (versus a benign etiology such as a granuloma). Also note that two of the cancers, breast and thyroid are treated differently from the rest as far as insurance approval.

The typical whole body exam covers the neck, chest, abdomen, and pelvis. The exception is melanoma where given its metastatic pattern imaging is performed from head to toe. Given the normally intense brain grey matter, PET is considered relatively insensitive for brain metastases. If this a consideration, infused MR (or even CT) is more accurate. Here is the list of currently approved whole body PET indications:

Non Small Cell Lung Carcinoma: Diagnosis, Staging, and Restaging

Lymphoma (Hodkins or Non Hodkins): Diagnosis, Staging, and Restaging

Head & Neck Carcinoma (excluding CNS tumors): Diagnosis, Staging, and Restaging

Melanoma: Diagnosis, Staging, and Restaging

Colorectal Carcinoma: Diagnosis, Staging, and Restaging

Esophageal Carcinoma: Diagnosis, Staging, and Restaging

Breast Carcinoma: Staging, Restaging (after completion of a course of therapy), Response to Therapy (during a course of therapy). Not diagnosis (such as working up an equivocal mammographic or clinical finding) or staging the axilla only when distant metastases are considered very unlikely.

Thyroid Carcinoma: Restaging residual or recurrent thyroid cancer of follicular cell origin (i.e. papillary or follicular cancers) that has been treated previously by thyroidectomy and radioablation and with serum thyroglobulin > 10ng/ml and a negative I-131 whole body scan. Just as for I-131 scans, accuracy of thyroid PET is increased with elevated patient TSH levels (hormone withdrawal method or rTSH [Thyrogen] administration).

Solitary Pulmonary Nodule (SPN): Differentiating early bronchogenic carcinoma from other benign nodules (commonly granulomas). This is indicated for those nodules under 4-cm with indeterminate characteristics on CT. If they are very suspicious for lung carcinoma (such as with obvious spiculations) and/or greater than 4-cm, they can still be evaluated by PET under the Non Small Cell Lung Carcinoma category above (diagnosis/initial staging).

    How small a SPN can I attempt to image on PET? There is no hard and fast answer but as a rule of thumb, any nodule 10-mm or over is a good candidate. Even nodules down to 7-mm can be often be accurately characterized on PET. Visible uptake is dependent on a number of factors including lesion size, location, and metabolic activity. The real question is what is the negative predictive value of PET because even a 2-mm nodule that is "hot" is very suspicious for malignancy. So nodules that contain 7-mm of solid tissue begin to fall into PET consideration. You can consult with a nuclear medicine attending or radiology resident to inquire about a specific case.

    Two additional points to remember for SPNs. First, while PET has an excellent accuracy for categorizing indeterminate SPNs, there are rare false negatives (such as with low grade tumors like broncoalveolar) and false positives (such as with "active" granulomas). So if a nodule is positive on PET, it is strongly suspicious for malignancy and biopsy should be strongly considered (and the patient can be staged on the same PET exam). If negative on PET, consideration should be made to follow these nodules on CT for a reasonable interval to establish stability and likely benignity. Those rare tumors that are falsely negative on PET are usually of lower grade with a better prognosis.
In addition to the indications above, PET provides similarly increased accuracy in evaluating other tumor types, and many private insurers will reimburse accordingly. Examples include cervical, ovarian, pancreatic, musculoskeletal, multiple myeloma, and carcinoma of unknown primary. Our schedulers at the University of Chicago PET Center will do most of the reimbursement inquiries for you. If coverage is denied, a patient may choose to pay for the exam themselves (although it is expensive—several thousand dollars). The list of "approved" whole body indications is growing every year. It is likely that cervical carcinoma with be the next cancer type to make the CMS list. Call 773-702-0336 (or 2-0336 from in-house) for inquiries.