Definition of medical terms used on the web.


Many tumors move with the patient breathing normally, which must be taken into account when planning treatment. Patients treated at MD Anderson with tumors that move may move with respiration are imaged with 4D CT , a special technique allowing tissue movement during breathing to be noted and taken into account when planning treatment. In some cases, breathing control techniques are used where the radiation beam will be activated only during a part of the respiratory cycle. This treatment is known as ‘gating’.

Gating can be done with the patient breathing normally or holding their breath. For gating during normal breathing, the radiation beam is activated only a certain part of the respiratory cycle, normally when the patient is breathing out.

For gating during breath-hold, the beam is activated only when the patient breathes in and holds their breath. This technique is used in left-sided breast irradiation. When the lungs are full of air, they push the heart down away from the wall of the thorax and the breast. In some cases, with left-sided breast cancer, delivery of the radiation beam during breath-hold reduces the exposure of the heart to radiation and prevents future cardiac injury.

In many cases the patient will be able to observe their breathing curve on a monitor to them help control their breathing, so that the treatment will as short and effective as possible.

Advantages: 4D CT allows the edges and movement of the tumor to be defined accurately. This means the fields of treatment are smaller and less toxic. It also means there is greater precision in the localization of the tumor, which increases the probabilities of controlling the disease.