Influence of Couch Tracking Motion

Radiation therapy is one of the main options in cancer treatments, alongside surgery and chemotherapy. Its efficacy largely depends on the absorbed radiation dose of the tumor cells. However, the irradiation of healthy cells results in negative side effects for the patient. Therefore, a big challenge in radiation therapy is to irradiate the tumor with sufficient dose, while keeping the irradiation of the healthy tissue reasonably low. Currently, the radiation treatment is planned by defining a volume enclosing the tumor, but with added margins to account for any uncertainties. These margins ensure that the tumor receives the prescribed dose.

Tumor motion contributes to the uncertainties. The tumor motions of tumors in different sites have different causes, but for this project the focus is on thoracic, liver, and adrenal gland tumors. The motion of these tumor types is mainly caused by the patient's respiration. So, the tumor motion pattern depends on the respiration pattern of the patient. The motion of lung tumors has been reported to have a peak-to-peak amplitude of up to 24 mm. Currently, the tumor motion is handled by enlarging the margins, such that the tumor is always inside the defined volume. But enlarging the margins also results in an increase of irradiated volume consisting of healthy tissue.

Tumor motion mitigation is concerned with reducing the margin increase caused by the motion of the tumor. There are several approaches to tumor motion mitigation and the one under consideration in this project is the tumor tracking approach, the technically most difficult approach. In tumor tracking the tumor motion is continuously compensated by moving the radiation source modifying the radiation beam, or moving the patient, which is denoted as couch tracking.

In couch tracking, the patient is moved by the robotic treatment couch. Such robotic treatment couches are in use with conventional, widely available C-arm linear accelerators, and, therefore, are readily available for implementing couch tracking. The patient is placed on a couch which moves in the opposite direction of the tumor motion. The goal is to minimize the patient's tumor motion relative to the radiation, which in turn allows the margins to be decreased. The margin decrease might ultimately lead to a reduction of side effects, e.g. pneumonitis.

The motion of the couch depends on the motion of the tumor, which in turn depends on the respiration of the patient. However, the couch motion may influence the patient's well being or the patient's respiration. So the question arises: Does the motion of the couch have an influence on the respiration behavior? And also: Does the motion of the couch have an influence on the well being (motion sickness)? And are the well-being and the respiration behavior connected? If the respiration behavior does depend on the couch motion, it may be necessary to control the respiration behavior. Additionally, in the study, the investigators will check an assumption in couch tracking, namely that the patient's body is rigidly fixed to the couch. If this assumption does not hold, the motion of the patient's body relative to the couch will have to be taken into account in couch tracking.