Tumors that originate in the brain are a relatively rare form of cancer, with only about 22,500 new cases diagnosed in the United States each year. The outlook for these patients is not good because most types of brain tumors are malignant and difficult to fully remove. Brain tumors account for only 1.4% of all cancers, but 2.4% of all cancer-related deaths. The American Cancer Society estimates that about 13,000 people will die annually from malignant brain tumors.
Source: American Cancer Society. Cancer Facts & Figures 2011. Atlanta: American Cancer Society; 2011
Tumors that originate in the brain are a relatively rare form of cancer. More commonly, tumors start in other organs such as the lung or breast and then metastatic disease spreads to the brain. Brain tumors are most often discovered because of symptoms that the patient has developed, symptoms caused by the degeneration of function in the area of the brain that the tumor is forming.
Once discovered, differentiating between primary brain tumors and metastatic disease is a key diagnostic point, and is confirmed by biopsy. Pinpointing the exact location to biopsy is difficult and can carry some risks, and physicians increasingly rely on medical imaging to help. MR and CT scans of the brain are used to look at the brain when an abnormality is suspected. These give exquisite detail of the structure and anatomy of brain tumors, but by adding metabolic information from a PET/CT scan, the physician can make a more precise determination of the location and extent of disease.
Fortunately, not all brain tumors are cancerous. Benign tumors do not metastasize and, with very rare exceptions, are not life-threatening. Cancerous tumors are “graded” by their level of aggressiveness and by the type of cells from which they grew. By studying the results of the PET/CT scan, a physician can separate a tumor as being high-grade, low-grade or benign, based on the degree of uptake of the radiopharmaceutical 2-Deoxy-2-[18F]fluoro-D-Glucose (FDG). Elevated FDG uptake in a brain tumor should be confirmed histologically, but is generally associated with a poorer prognosis compared with brain tumors with lower levels of FDG uptake.
Early determination of the grade of the tumor and how far it has spread helps the physician select the most appropriate treatment.
In the majority of cases, brain tumors are treated by surgery, alone or in combination with other treatments, such as radiotherapy or chemotherapy.
Before treatment, physicians utilize PET/CT scan results to guide treatment decisions by separating a tumor as being high-grade, low-grade or benign based on the degree of FDG uptake. A baseline PET/CT scan provides physicians with pretreatment information concerning the extent of disease, which can be compared after treatment with follow-up scans to determine whether treatments have been effective.
PET/CT imaging is a good tool for physicians to use to help determine the grade of the cancer, locate distant metastases, determine the best treatment approach, and assess if the treatment was effective.
A PET/CT scan can show where tumor cells are growing, which helps your doctor determine the best course of treatment.
Your doctor will schedule you for routine follow-up visits, depending on the stage of the cancer, and may order follow-up imaging tests. By comparing the FDG uptake in pre and post-treatment PET/CT scans, physicians can determine if lesions have fully regressed and if the treatment has been successful.
Many brain tumors have a risk of recurrence, and if the cancer does return, it is important that additional treatment begin immediately. Medical imaging is increasingly utilized to detect recurrent disease.
Anatomical imaging, such as MRI, shows changes in the structure of the brain, but fails to clearly differentiate recurrent tumor from scar or postradiation effects. After the completion of radiation therapy, contrast enhancement on CT or MRI in the area of the previous tumor mass may represent viable tumor or could represent radiation necrosis. When there is FDG uptake in the lesion, it strongly suggests the presence of residual tumor, whereas absence of FDG uptake suggests that necrosis is present.
A PET/CT scan can be used to image tumor response to therapy and to detect recurrence in treated lesions.