Inter- and intrafractional movement of the tumour in extracranial stereotactic radiotherapy of NSCLC

Purpose. The purpose of this study is to determine the inter- and intra-fractional respiration induced tumour movements as well as setup accuracy in a stereotactic body frame for stereotactic treatments of NSCLC patients. Patients and methods. From August 2005 to March 2008, 26 patients with NSCLC where given a stereotactic treatment. The patients were scanned with normal and uncoached respiration without use of abdominal compression. Each patient had CT-scans performed at four occasions throughout the treatment: As part of the CT-simulation and before the three radiotherapy treatments. At every occasion five individual CT-scans covering the tumour volume were obtained. In this way 20 scans where obtained from each patient. In each CT-scan the maximum positions of the tumour where located in all six directions, represented by the top, bottom, anterior, posterior, left and right part of the tumour. These coordinate constitute the data of this study. Results. The standard deviations of the respiration induced intra-fractional movements were: LR: 0.9 mm, AP: 1.6 mm and CC: 2.0 mm (1 SD). The inter-fractional movements were: LR: 1.1 mm, AP: 1.3 mm and CC: 1.7 mm (1 SD). Finally the set up accuracies in the body frame were LR: 1.5 mm, AP: 1.1 mm and CC: 1.7 mm (1 SD). Discussion and conclusions. Consecutive CT scans can be used to evaluate the respiration induced tumour movement. For patients immobilized in a stereotactic body frame, large movements of the tumour are rarely seen within the lung. With consecutive scans, using a conventional CT-scanner, it is possible to select those patients in whom the tumour movement is large. Application of 4D CT and Cone beam verification is strongly encouraged to minimize the requested treatment margin.