Image generated from Lung 4DCT -
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Four-Dimensional Computed Tomography (4DCT) represents the next step forward in imaging. New technology makes taking a CT image much faster and more accurate than before. 4DCT uses this technology to take images that don't just capture the tumor, but also capture the movement of the body's organs or of the tumor over time. This is very important for tumors located on or near organs that move, in that it makes treatment much more accurate.
Taking a 4DCT image is similar to traditional CT scanning. In the procedure, the patient lies on his or her back. A scanner spins around the patient in a corkscrew path, taking constant images for the approximately 30 seconds it takes to complete its path. The images make a 3D image showing the body's breathing, which also shows how the tumor moves or is affected by moving organs nearby.
This information allows for the design of more accurate treatment. For instance, a tumor on the lung will move along with each breath as the lung inflates and deflates. Using traditional imaging, the oncologist would know where the tumor is positioned at only one point in the breath. Radiation could then be aimed at the tumor, but the beam would only hit the tumor as intended during the one point of the breath matching the image; at other times, the beam could miss the tumor, or healthy tissue would be irradiated. To compensate for this possibility, lower, less effective levels of radiation would have to be used to reduce damage, reducing the effectiveness of the entire treatment.
The information gathered from 4DCT allows for radiation to be delivered to the tumor within a certain interval in the breathing cycle. This is done using gated IMRT, a form of IMRT where the radiation is stopped when the tumor is not in the correct position. This allows the use of higher, more effective levels of radiation while minimizing the impact on healthy tissue, making new levels of treatment possible.
