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Most radiation therapy is planned using the results of a 3D CT scan. A 3D scan largely presents a snapshot of the body at a particular point in time, however due to the time of the acquisition, in which the patient is likely to have moved in some way (even if only breathing), there will be an element of blurring or averaging in the 3D scan. [ 6 ]
A CT scan is often the primary image set for treatment planning while magnetic resonance imaging provides excellent secondary image set for soft tissue contouring. Positron emission tomography is less commonly used and reserved for cases where specific uptake studies can enhance planning target volume delineation. [ 9 ]
The radiation used in CT scans can damage body cells, including DNA molecules, which can lead to radiation-induced cancer. [148] The radiation doses received from CT scans is variable. Compared to the lowest dose X-ray techniques, CT scans can have 100 to 1,000 times higher dose than conventional X-rays. [149]
Compared to most other diagnostic imaging procedures, CT scans result in relatively high radiation exposure. This exposure may be associated with a very small increase in cancer risk. The question is whether that risk is outweighed by the benefits of diagnosis and therapy [8] The procedure has a low rate of finding disease.
Modern radiation therapy relies on a CT scan to identify the tumor and surrounding normal structures and to perform dose calculations for the creation of a complex radiation treatment plan. The patient receives small skin marks to guide the placement of treatment fields. [10]
X-ray computed tomography (CT), or Computed Axial Tomography (CAT) scan, is a helical tomography technique (latest generation), which traditionally produces a 2D image of the structures in a thin section of the body. In CT, a beam of X-rays spins around an object being examined and is picked up by sensitive radiation detectors after having ...
The currently used low dose CT scan results in a radiation exposure of about 2 millisieverts (equal to roughly 20 two-view chest x-rays). [11] It has been estimated that radiation exposure from repeated screening studies could induce cancer formation in a small percentage of screened subjects, so this risk should be mitigated by a (relatively ...
After initial concern that CTPA would miss smaller emboli, a 2007 study comparing CTPA directly with V/Q scanning found that CTPA identified more emboli without increasing the risk of long-term complications compared to V/Q scanning. [3] A V/Q scan may still be recommended when a lower radiation dose is required. [4]