Usefulness of PET scans
Peeyush Bhargava, MD
Last Modified: October 27, 2002
Dear OncoLink "Ask The Experts,"
I have heard that there is a new scan for cancer patients? that is called a PET scan. They say that it lets doctors detect the exact location of the cancer. This keeps patients from having to have surgery to locate the cancer. Can you tell me more?
Peeyush Bhargava, MD, Chief Fellow in the Department of Nuclear Medicine at the University of Pennsylvania, responds:
PET scans have been around for quite a long time but they have recently gained popularity in the management of a variety of cancers. They are useful in the diagnosis, the initial staging (to decide the treatment modality best suited for that stage of the disease) and restaging (monitoring response to therapy). Currently, PET scans are commonly used in the management of patients with lung cancer, colon cancer, melanoma, lymphoma, head and neck cancer, esophageal cancer and breast cancer.
Typically, in a whole body FDG PET scan, the patient is scanned from the chin down to the upper thighs and additional images are required if there are further areas of concern. Sometimes they show wide spread disease which makes the cancer inoperable. At other times, the PET scan rules out metastases indicating that the patient is a good candidate for curative surgery. PET scans are also very useful in evaluating suspicious findings on other studies such as CT scans and MRI's. They may be useful in detecting recurrent or residual disease in patients who have been treated for cancers and the follow up blood test (for example: CEA for colon cancer, CA 125 for ovarian cancer) is abnormal.
Please see the example below. These are the images of a patient who was recently diagnosed with lung cancer. The patient was being considered for surgical resection of the lung cancer. Image 1 is from the patient's CT scan that shows a mass in the right lung (outlined by the red arrows) and suggests malignancy. A whole body PET scan was performed for staging the lung cancer (to decide whether the cancer is operable or not). Image 2 is the whole body FDG PET image. The body contour has been outlined for better visualization. It shows a large area of intense activity (bigger red arrow) in the right lung that corresponds to the mass described in the CT scan. Also seen are multiple scattered foci of intense activity (smaller red arrows) suggesting diffusely scattered soft tissue and bony metastasis. Clearly this patient is not a candidate for curative surgery as the cancer has spread all over the body. The green arrow on image 2 points to normal activity in the urinary bladder. This example clearly illustrates how the FDG PET scan may help in staging patients with lung cancer.