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Clinical Updates
PET/CT offers unique advantages in evaluating cancer treatment
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PET/CT — an imaging technique that combines positron emission tomography and computed tomography — has become an important tool in helping physicians diagnose and manage many types of cancers because of its unique ability to simultaneously image physical structures and biological processes. In addition to its use in diagnosing and staging cancer, PET/CT is changing how cancer therapies are evaluated by predicting therapeutic responses very early in the course of therapy.
Taking advantage of the fact that aggressive tumors often consume large amounts of sugar to fuel their growth, physicians use 18F-fluorodeoxyglucose (FDG) — a radio-labeled glucose — to reveal a tumor’s metabolic activity. These images of tumor glucose use are fused with CT images that show anatomic structures with great accuracy.
Determining chemotherapy response
In many cases, physicians can use PET/CT to determine if a chemotherapy treatment is effective after as little as a single treatment cycle. Based on changes in the tumor’s glucose metabolism, physicians can decide if the chemotherapy treatment should continue or if they should switch to another treatment modality. This early determination helps ensure that patients are receiving effective therapies in a timely manner and it reduces their exposure to the potentially harmful effects of treatments that ultimately will prove ineffective in treating their cancer.
PET/CT can provide excellent treatment response data for most cancers, including:
• lung cancer
• lymphoma
• breast cancer
• melanoma
• colorectal cancer
Some cancers, including prostate cancer, are not effectively imaged using this technique because they don’t metabolize a significant amount of glucose. This can indicate that the cancer is not very aggressive, but could instead mean that its growth is being fueled by something other than glucose, such as fatty acids or amino acids.
Radiation therapy planning
PET/CT is also being used to improve radiation therapy planning. By using the glucose uptake information provided by PET/CT, physicians are able to specifically target the metabolically active portions of the patient’s tumor — they can increase the radiation dose to active areas while reducing the dose to adjacent areas. PET/ CT can be used to monitor the efficacy of radiation therapy in the same way it is used to monitor chemotherapy treatments; physicians can look for a decrease in the tumor’s metabolic activity following one or more rounds of treatment.
About the procedure
Following the injection of the radioisotope, the patient waits for 45 minutes to one hour for the radio-labeled sugar to distribute throughout the body. The patient is then scanned, which takes about 20 minutes. Because cancer is a systemic disease, whole-body scans are performed to detect the full extent of the disease.
The same equipment can be used for standard CT protocols with intravenous contrast and all other imaging studies that would normally be performed using a stand-alone CT scanner. This offers patients the convenience of having multiple imaging studies performed at the same time and location.
PET/CT evaluation of cancer patients is available both at UCLA Medical Center, Santa Monica and at Ronald Reagan UCLA Medical Center.
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