CyberKnife radiosurgery for an intracardiac metastasis.

1 of 2 DESCRIPTION Intracardiac tumours move both with breathing and with the cardiac cycle; they therefore pose unique problems for radiotherapy delivery. Conventional radiotherapy must encompass the tumour with a margin to account for this motion, and the prescription is limited by myocardial radiation tolerance. The greater accuracy of radiosurgery allows higher radiation-dose deposition, with relative myocardial sparing. A 67-year-old male underwent surgical resection of a right-ventricular metastatic adenocarcinoma in March 2009, followed by postoperative conventional radiotherapy close to myocardial tolerance (40 Gy in 20 fractions). Six months later the tumour regrew, obstructing the ventricle and leading to heart failure, with a prognosis of days. Further surgery was not possible. He was treated with fractionated radiosurgery (25 Gy in fi ve fractions) using the CyberKnife system (Accuray, Sunnyvale, California, USA) ( fi gure 1 ). Implanted pericardial fi ducial markers allowed near realtime x-ray monitoring of the tumour and heart position with breathing. The integrated Synchrony system correlated fi ducial position with real-time monitoring of chestwall movement, enabling the radiation beam to track the moving tumour continuously. Cardiac cycle motion was accounted for by outlining the tumour position on three different phases of a cardiac-gated CT scan, fused with the radiotherapy planning CT ( fi gure 2 ). Echocardiography showed a 27% reduction in crosssectional tumour area at 1 week following treatment, and Images in...