PET-CT is an investigation that today is part of the protocol for the diagnosis, treatment and monitoring of many cancers. PET-CT deals with nuclear medicine experts – a cutting-edge field in modern medicine – whose applications are of utmost utility in cancers, but also in other disorders. There are over 100 types of malignancies, and each cancer case has its own peculiarities. These can be viewed and evaluated thanks to the cutting-edge technologies in nuclear medicine, and the information that PET-CT offers is essential in long-term diagnosis, treatment and monitoring. Every top center in the world dealing with cancers deals with each case in multidisciplinary committees of oncologists, surgeons, doctors of various specialties, radiotherapists, anatomopathologists, imaging experts and nuclear medicine. And the ACIBADEM Group of Hospitals is among the elite centers, where nuclear medicine experts are instrumental in successfully treating patients. One of the most experienced physicians is Prof. Dr. Erkan Vardareli of the ACIBADEM Altunizade Hospital, which describes extensively the usefulness of PET-CT in topical oncology medicine.
Prof. Dr. Erkan Vardareli: PET-CT is a combination of PET, positron emission tomography and CT, computed tomography. In diagnostic medicine, we have been using computed tomography (CT) for years to scan the body and evaluate the patient’s anatomical details in screening or diagnostic situations. And positron emission tomography (PET) can provide us with information on how radiopharmaceuticals – radiolabelled substances in which we can assess the physiology of certain diseased tumors or tissues are received in various malignant tissues from the body. Thus, combining in the same investigation positron emission tomography with computed tomography provides both anatomic and functional metabolic information about the tumors we investigate. The indication of PET-CT is in the diagnostic protocol, the staging of malignant disease and in monitoring the body’s response to treatment. Also, in some cases, PET-CT helps us to establish the radiotherapy plan for metabolic active tumors or metastases. Also, with PET-CT we can evaluate the outcome of both immunotherapy and target therapies. We can assess glucose metabolism, the so-called SUV, the standardized uptake value, before and after therapy. If this is reduced during therapy, it is an indication that treatment works. SUV is one of the important criteria for assessing the success of oncology treatment today.
Prof. Dr. Erkan Vardareli: The most used substance in PET-CT is radiolabelled glucose, 18F-FDG. In a first step, we inject the radiopharmaceutical, such as FDG radioactively labeled glucose, wait for an hour, and then scan the patient’s body. Then, we see the areas with high metabolism of glucose, which means the presence of malignant cells. Today, in addition to FDG, we can also use other substances, such as galactose-labeled gallium-68 PSMA (gallic membrane-specific prostatic antigen) for prostate or gallium 68-DOTATED for neuroendocrine tumors. They can not be seen with FDG. Thus, CT PET scanning can be used for most malignant tumors, primary tumors or metastases, to diagnose them, monitor therapy to assess their status to plan radiotherapy. The patient does not have to eat for 6 hours, he can only drink water before the procedure. When it comes to us, it is injected with the radiopharmaceutical, there are no contraindications or allergic reactions. Then we wait between 45 minutes and one hour, and the screening takes between 15 and 20 minutes. This is the procedure for F18-FDG. For galium 68, no 6-hour food break. Depending on the situation, the result can be obtained on the same day or day.
Prof. Dr. Erkan Vardareli: Cancers do not resemble each other, and each case has its own peculiarities. For example, invasive breast ductal carcinomas have a higher affinity for FDG, unlike lobular breast carcinoma. And if you do PET-CT for lobular carcinoma, you can not see the lesions. So, in breast carcinoma, we only make PET-CT in high affinity types for FDG, such as invasive ductal carcinoma or ductal carcinoma in situ. So, PET-CT differs from other imaging investigations in that not all tumor types have affinity for FDG. Through PET-CT, we scan the whole body through a single imaging method, unlike other methods by which each area of the body is investigated differently. Therefore, PET-CT is important for assessing the physiological activity of malignant tissue in any area of the body. There are cases when we investigate drug-treated malignant tissue that is not yet operated but has a reduced metabolic activity after therapy. Thus, PET-CT helps us evaluate the body’s response to treatment, with several criteria for assessing resistance to treatment.
Prof. Dr. Erkan Vardareli: PET-CT is very important in the protocol which sets the most appropriate cancer treatment, especially in the case of personalized molecular therapies. We use tracking molecules in certain types of disease. Let’s take the example of prostate carcinoma. In this case, we can make PET-CT with gallium 68 PSMA. If malignant prostatic lesions express the membrane-specific prostate antigen, then we can radiolabe it with lutetium, erbium or actinium and thus we can treat these types of tumors with high energy radioactive components. We can do these therapies in advanced stages of prostate cancer to improve the survival rate. In the early stages, other therapies such as surgery, chemotherapy and radiotherapy are applied. In the screening and diagnosis of prostate cancer, magnetic resonance is useful. But to detect the disease outbreak before biopsy, we use PET-CT with 68-PSMA gallium.
Prof. Dr. Erkan Vardareli: This depends from the patient to patient and from affection to affection. If we are talking about lung carcinoma, the accuracy is 95 percent. In other types of cancer, it may be lower because glucose metabolism is not as intense. Accuracy is variable, but it is at least 90 percent for all malignancies.
Prof. Dr. Erkan Vardareli: We can use PET-CT in patients with neurological problems, to investigate epileptic outbreaks in the brain, in dementia cases, for diagnosis differentiated in Alzheimer’s, cardiovascular disease after myocardial infarction, to see if there is still healthy heart tissue that can be revascularized. PET-CT is the gold standard to detect viable cardiac tissues after a myocardial infarction. Thus, according to PET-CT results, physicians can take the best therapeutic decisions for patients. For example, in the case of patients with infarction, if after PET-CT it is found that there is viable tissue, a bypass surgery can be made for the revascularization of the area. Otherwise, if there is no viable tissue, the operation is of no use. The decision is based on PET-CT. And, in the case of heart patients, we use FDG.
Prof. Dr. Erkan Vardareli: An important indication for PET-CT is to evaluate the body’s response to oncology treatment. Follow-up programs are important for oncology patients to assess possible relapses or metastases.
Prof. Dr. Erkan Vardareli: In some tumors, marker evaluation is an important citation in follow-up programs, but it is not the only one. So, in some types of cancer such as colon, breast and ovarian carcinoma, we correlate FDG consumption assessed by PET-CT by tumors with tumor markers.
Prof. Dr. Erkan Vardareli: I prefer to do PET-CT after biopsy. The anatomopathological report gives us information about the type of tumor cells, invasiveness, and other aspects that we have to consider.
Prof. Dr. Erkan Vardareli: Yes, patients with diabetes are special cases for us if they need PET-CT with FDG. The blood glucose level should be below 200 for the investigation. Thus, if diabetes is under medication control, and blood glucose is below 200, there are no problems. But if blood glucose is greater than 200, we can not make PET-CT with FDG due to false negative results that may occur.
Prof. Dr. Erkan Vardareli: We can also make PET-CT in newborns, but there are different regulations for adults. The level of radiopharmaceuticals is adapted to children and we can do all the procedures in nuclear medicine. But in their case, we need anesthesia to be able to do the procedure.
Prof. Dr. Erkan Vardareli: Some patients ask us if they can use PET-CT as a screening method. There are families with oncological history, people with first degree relatives diagnosed with various types of cancer. If there is, for example, a history of family-based breast carcinoma, PET-CT can be used as a screening method.