In certain locations of the body such as the lungs, gastrointestinal tract, and pelvis, respiratory (breathing) motion leads to significant movement of your tumor and critical organs. In the past, respiratory motion has hindered doctors' ability to accurately map out the tumor and deliver radiation specifically to your tumor and not your normal tissue. At UCLA, we use an advanced technology that tracks your breathing, as well as the location of your tumor, allowing us to target your tumor accurately and precisely (Figure 1).
Figure 1:Gating Procedure
Future Technology - Will allow for "tracking" of tumor
How does respiratory gating work?
By using a special CT scan (4-dimensional CT scan) at the time of your radiation simulation, where we factor in time, we are able to obtain a movie of your body (Figure 2). This maps out not only the anatomical location of your tumor, but also where your tumor is located at a specific point in your breathing cycle. Using a special respiratory gating software, and integrating it into your radiation treatment planning, we then define a specific window in your breathing cycle, much like a baseball strike zone, when it is optimal to turn on the radiation beam. Ideally, this "strike zone" is a period of time in your breathing cycle that your tumor moves the least. Although your radiation treatment will take longer using this technology, the field of radiation is smaller and much more precise. Respiratory gating is often combined with intensity modulated radiation therapy to optimally deliver a precise dose to your tumor and spare your normal tissue.
Why is respiratory gating better?
Figure 2: 4-D CT Scan showing tumor movement in the lung.
Radiological treatment can be challenging due to the natural movement
of the body. UCLA uses cutting-edge technology to better understand movement
patterns specific to our individual patients - allowing for a more personalized and
precise treatment plan.
Before respiratory gating was possible, doctors often were not sure of the location of your tumor while you breathe. Therefore, doctors incorporated a large margin (1-2 cm usually) around where your tumor appeared to be to ensure appropriate coverage and dosing of the radiation. However, this led to unnecessary delivery of radiation to your normal tissue, causing unwanted short-term and long-term side-effects. In many cases, this roadblock prevented the delivery of adequate radiation doses to your tumor.
Respiratory gating eliminates unnecessary and harmful radiation to such a broad area, and focuses more radiation onto your tumor, while sparing more healthy tissue. Respiratory gating is most useful for tumors that have the most motion, such as lung tumors, and gastrointestinal tumors.
This technology, in some cases, makes it possible to limit the number of treatments that is needed, and therefore allows fewer visits to the radiation oncology department. It makes it easier for patients to receive their treatments in its entirety.
