Varian Respiratory Gating System’s Application In Lung Cancer Treated By Cyber Knife

Respiratory movement is an important element that influences stereotactic radiotherapy of lung cancer, because the identification of internal target volume(ITV) is difficult. Synchrony is the greatest advantage of lung cancer treated by Cyber Knife. It implants cylindrical Fiducials into someplace around focal lesion of patients by B-scan or CT-guided puncture. At the beginning of treatment, patients wear synchronous respiratory track vest to gain wave of whole respiratory process. At the same time, it can shoot a series of x-ray lung film to acquire position of Fiducials at different breath stages and establish mutual relationship between Fiducials position and breath wave. It can guide mechanical arm to control ray cluster to move with patients ’ breath rhythm. It realizes real-time tracking of tumor by ray. The technology frees doctors from considering influence of tumor moving with breath movement in contouring target volume, reducing range of contouring target volume and shrinking normal organization range around tumor.But in the clinical practice, a part of patients can not accept Fiducials implanting surgery because of refusing or lower pulmonary function. To these patients, we should better use 4D-CT location scanning method to identify movement range of tumor in breath process to find the boundary of ITV. When treating, Xsight-Spine technology is often used. But 4D-CT scanning technology machine requires relatively high configuration. The scanning process is more complicated than common locating CT scanning. Patients will receive more radiation dose in 4D-CT scanning than that in CT scanning.Therefore, the research chooses 37 lung cancer patients treated by Cyber Knife to get real-time respiratory phase of the patients, observe patients ’ breath wave to train expiration, end-inspiratory hold and scan CT photo sequence of expiration and end-inspiratory hold by Real-time Position Management(RPM) to find three-dimensional coordinate of tumor center in two figure sequence. Compare it with three-dimensional coordinate of tumor center in expiration, end-inspiratory hold sequence of the same patient and analyze it to get difference of each lesion of patients to provide evidence for clinical work.The research results prove the differences are influenced by the following elements: The coordinate difference value increases as age growing. As fo r the same patient, lesion has the greatest difference in lower part of lung, then the middle of it and at last the upper part of lung.