PET Scans (Positron Emission Tomography)

Since the turn of the millennium we are now using PET scans (which tag radioactive glucose metabolism) to evaluate the spread and activity of cancer. PET scans are more sensitive than other tests in evaluating cancer patients for many forms of cancer.

 Picture at the left is a PET scan showing colon cancer that has spread from the pelvis region to the liver. PET scans are much more sensitive than CT scans (see head and neck, lymph nodes,  lung,  more lung, liver , liver more liver,  bone and bone for some good examples.) Some comparisons from the literature are noted below:


Understanding the basics of pet scans. and atlas here

wbsmall.gif (61060 bytes)

picture on left is  CT scan in upper mediastinum with lymph nodes and vessels in a patient with  lung cancer. The PET scan (on the right) lights up the structures that contain cancer, thus helping prove that the cancer has already spread to these lymph nodes and changing the patient's stage from stage I to stage III and eliminating surgery as a good treatment option.

same patient lower in the mediastinum, again the PET helps identify the malignant lymph nodes and avoids confusing these structures with normal blood vessels
Test Accuracy
Cancer Type PET Scan CT or mammogram
Lung Cancer 81% 52%
Colon Cancer 95% 68%
Breast Cancer 85% 67%
pet_dementia.jpg (2617 bytes) The radioactivity used in a PET scan is attached to glucose and shows metabolism, in the brain normal metabolism and brain activity shows up as dark areas, with loss of brain function (e.g. dementia) will cause the PET to look more washed out (arrows.) (For comparison pictured at far left an MRI of doctor miller (on left) compared (middle) with a typical hospital administrator and (on the right) a typical urologist.
PET scan are useful for staging (determine if the cancer has spread to other sites) it is useful for determining response top treatment (if the cancer becomes less intense (decrease in the SUV number) then that correlates with a good response to therapy and predicts a better outcome.) If the cancer has a high SUV (i.e. rapid growing and using up allot of glucose) then it may be a more aggressive or rapid growing cancer and have a worse prognosis as in the study of sarcoma patients noted below
SUV Score Survival/5 years
< 1.5 84%
1.5 - 3.6 45%
> 3.6 38%
Prognostic significance of preoperative [18-F] fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging in patients with resectable soft tissue sarcomas.

Schwarzbach MH, Department of Surgery, University of Heidelberg,  Ann Surg. 2005 Feb;241(2):286-94.

OBJECTIVE: The objective of this study was to evaluate the prognostic significance of preoperative positron emission tomography (PET) using 2-fluoro-2-deoxy-D-glucose (FDG) by calculating the mean standardized uptake values (SUV) in patients with resectable soft tissue sarcomas (STS). In 55 cases, STS were completely resected: 5-year recurrence-free survival rates in patients with SUV <1.59, 1.59 to <3.6, and > or =3.6 were 66%, 24%, and 11%, respectively (P = 0.0034). SUV was a predictor for overall survival (5-year rates: 84% [SUV <1.59], 45% [SUV 1.59 to <3.6], and 38% [SUV > or =3.6]; P = 0.057) and local tumor control (5-year rates: 93% [SUV <1.59], 43% [SUV 1.59 to <3.6], and 15% [SUV > or =3.6]; P = 0.0017).

 

Intensity of 18Fluorodeoxyglucose Uptake in Positron Emission Tomography Distinguishes Between Indolent and Aggressive Non-Hodgkin’s Lymphoma
Heiko Schöder,   JCO Jul 20 2005: 4643–4651.

PET studies of 97 patients with non-Hodgkin's lymphoma who were untreated or had relapsed and/or persistent disease and had not received treatment within the last 6 months were analyzed, and the highest standardized uptake value (SUV) per study was recorded. Correlations were made with histopathology. FDG uptake was lower in indolent than in aggressive lymphoma for patients with new (SUV, 7.0 ± 3.1 v 19.6 ± 9.3; P < .01) and relapsed (SUV, 6.3 ± 2.7 v 18.1 ± 10.9; P = .04) disease. Despite overlap between indolent and aggressive disease in the low SUV range (indolent, 2.3 to 13.0; aggressive, 3.2 to 43.0), all cases of indolent lymphoma had an SUV ≤ 13. A receiver operating characteristic (ROC) analysis demonstrated that the SUV distinguished reasonably well between aggressive and indolent disease (area under ROC curve, 84.7%), and an SUV > 10 excluded indolent lymphoma with a specificity of 81%. With a higher cutoff for the SUV, the specificity would have been higher.

CONCLUSION: FDG uptake is lower in indolent than in aggressive lymphoma. Patients with NHL and SUV > 10 have a high likelihood for aggressive disease. This information may be helpful if there is discordance between biopsy and clinical behavior.