Positron emission tomography (PET) is an advanced diagnostic imaging technique that is used for diagnosis, staging and restaging of various cancers. This technique exploits the increased metabolism of glucose in malignant viable cells. 2-[fluorine18]-fluoro-2-deoxy-D-glucose (FDG) which is an analogue of glucose detects the difference in glucose metabolism. Like glucose, FDG is transported into tumor cells, by means of glucose transporter protein and subsequently it is phosphorylated by an enzyme hexokinase to FDG-6-phosphate. As FDG-6-phosphate is not a substrate for glucose-6-phosphate isomerase (the next step in glycolysis), it is biochemically trapped within the cell. This process of metabolic trapping in cell constitutes the basis for imaging of distribution of tracer with PET. Since there is many fold increase in glucose metabolism in malignant tumors as compared to normal, it is easy to detect this difference in metabolism using PET. Therefore PET has high sensitivity and high negative predictive value as compared to conventional morphological modalities like computed tomography (CT), ultrasonography (USG), magnetic resonance imaging (MRI), which use size / density changes as the only or major criterion to distinguish between benign and malignant diseases. PET has well-established role in initial staging, restaging and monitoring the response to the therapy in the management of various cancers.
Fusion of PET & CT allows precise localization of the diseased sites, for optimal management of patient with cancer. Co-registration of a structural and functional image provided by PET – CT is essential for accurate planning of surgical procedures. Likewise, PET – CT imaging is becoming a standard of care in Radiation Oncology. PET guided IMRT can selectively target head and neck cancers, while reducing critical normal tissues. Staging, early response evaluation, detection of recurrence and follow-up of most of the malignancies can be done with this modality
We have standardized side by side fusion of PET – MRI images, which provide excellent soft tissue delineation with metabolic parameters, and are now being routinely used in Head & Neck cancers & also in Gynaecological Malignancies.
18 F FDG PET CT is done for the following indications:
Specialized PET CT procedures with 68Ga DOTA & PSMA peptides
68 Ga PET CT is done for Neuroendocrine tumors with DOTATOC and for Prostate cancer with PSMA for the following indications: