A number of medical conditions involve creating lesions whose positions are significant during the course of treatment, such as lesions that are located on the heart or on other organs close to the heart. In many cases, it is necessary to create lesions on anatomical regions that undergo rapid motion, for example motion due to pulsating arteries. Traditionally, the creation of such lesions or moving anatomical regions has required invasive surgery, such as open heart surgery for cardiac-related treatments.
As one example, atrial fibrillation is a medical condition characterized by an abnormally rapid and irregular heart rhythm, because of uncoordinated contractions of the atria (i.e. the upper chambers of the heart.) A normal, steady heart rhythm typically beats 60-80 times a minute. In cases of atrial fibrillation, the rate of atrial impulses can range from 300-600 beats per minute (bpm), and the resulting ventricular heartbeat is often as high as 150 bpm or above. A curative surgical treatment for atrial fibrillation that is known in the art is the so called “maze procedure,” which is an open heart procedure involving incisions and ablations of tiny areas of the atria. The surgeon makes a plurality of incisions or lesions in the atria, so as to block the re-entry pathways that cause atrial fibrillation. Upon healing, the lesions form scar tissue, which electrically separate portions of the atria, and interrupt the conduction of the abnormal impulses. While this procedure can be effective, with a high cure rate, the procedure is long and difficult to perform.
In general, possible complications of an invasive surgery are significant, and include stroke, bleeding, infection, and death. One technique for avoiding the complications of invasive surgery is radiosurgery, which is recognized as being an effective tool for noninvasive surgery. Radiosurgery involves directing radiosurgical beams onto target regions, in order to create lesions to necrotize tumorous tissue. The goal is to apply a lethal or other desired amount of radiation to one or more tumors, or to other desired anatomical regions, without damaging the surrounding healthy tissue. Radiosurgery therefore calls for an ability to accurately direct the beams upon a desired target, so as to deliver high doses of radiation in such a way as to cause only the target to receive the desired dose, while avoiding critical structures. The advantages of radiosurgery over open surgery include significantly lower cost, less pain, fewer complications, no infection risk, no general anesthesia, and shorter hospital stays, most radiosurgical treatments being outpatient procedures.
In order to avoid the disadvantages of invasive surgery, such as the open heart surgical procedure described above, it is desirable to provide a method and system for using radiosurgery to treat diseases that require the creation of lesions in specifically targeted anatomical regions. These anatomical regions may be located on a beating heart wall of a patient, or on organs near the heart. Alternatively, these anatomical regions may be located in other places within the patient's anatomy that undergo motion, e.g. due to pulsating arteries.
For these reasons, is desirable to provide a method and system in radiosurgery for precisely applying radiosurgical beams onto these moving anatomical regions of a patient.