OCTOBER 20239The advantage of PET/CT is the ability to see the metabolically active cancer cellsPositron Emission Tomography with CT (PET/CT)Positron emission tomography generates images of the metabolic activities of cancer cells in the patient. This is done by intravenous injection of sugar that is bounded to a radioactive tracer (18-fluorodeoxyglucose) to the patient. Once the patient is positioned inside the tomography unit, the sugar is metabolically absorbed by the cancer cells, and the radioactive tracers (annihilation radiation) are detected by the ring of detectors located inside the tomography unit. The end result is the volumetric images of metabolically active cancer cells fused with CT images of the patient, hence called PET/CT. The reason why image fusion of CT is necessary is that PET itself does not provide adequate information about the physical anatomy of the patient to properly identify and locate the metabolically active cancer cells within the patient. By fusing the CT images with the PET images, the clinician can clearly identify and orient where the metabolically active cancer cells are located with respect to the patient's anatomy. The advantage of PET/CT is the ability to see the metabolically active cancer cells. Images like CT and MRI may show the solitary mass, but the mass may not necessarily be an active cancer (for example, it can be fibrotic tissue that looks similar to the solid tumor in CT images). PET/CT can provide supplemental information about the metabolic activity of the cancer cells. Typically, PET/CT is used in lung cancer and metastatic cancers to supplement the CT images in radiation therapyImaging Modality Integrated within Linear AcceleratorBecause the localization of cancers at the time of treatment is critical to the treatment outcome, multiple imaging modalities have been integrated with a medical linear accelerator. A medical linear accelerator is a machine that generates high energy X-rays that can deliver radiation with pinpoint accuracy to the target, provided that the target inside the patient can be localized. For this reason, there has been a significant push for the integration of various volumetric imaging modalities with linear accelerators. The most common integration is with cone beam CT. MRI has also been integrated into the linear accelerator in order to exploit the benefits of soft tissue contrast. Most recently, the integration of PET has been introduced to the market. By integrating various imaging modalities with the treatment machines, clinicians are able to better localize the tumor at the time of the treatment. The advantage of the integration is the ability to increase the radiation dose to the cancer while minimizing the dose to critical structures. IMAGING APPLICATION IN RADIATION THERAPY
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