Quantifying Interfraction and Intrafraction Tumor Motion in Lung Stereotactic Body Radiotherapy Using Respiration-Correlated Cone Beam Computed Tomography
Received 25 July 2008; received in revised form 7 November 2008; accepted 18 November 2008. published online 22 April 2009.
Purpose
Stereotactic body radiation therapy (SBRT) is an effective treatment for medically inoperable Stage I non–small-cell lung cancer. However, changes in the patient's breathing patterns during the course of SBRT may result in a geographic miss or an overexposure of healthy tissues to radiation. However, the precise extent of these changes in breathing pattern is not well known. We evaluated the inter- and intrafractional changes in tumor motion amplitude (ΔM) over an SBRT course.
Methods and Materials
Eighteen patients received image-guided SBRT delivered in three fractions; this therapy was done with abdominal compression in four patients. For each fraction, cone beam computed tomography (CBCT) was performed for tumor localization (± 3-mm tolerance) and then repeated to confirm geometric accuracy. Additional CBCT images were acquired at the midpoint and end of each SBRT fraction. Respiration-correlated CBCT (rcCBCT) reconstructions allowed retrospective assessment of inter- and intrafractional ΔM by a comparison of tumor displacements in all four-dimensional CT and rcCBCT scans. The ΔM was measured in mediolateral, superior-inferior, and anterior-posterior directions.
Results
A total of 201 rcCBCT images were analyzed. The mean time from localization of the tumor to the end-fraction CBCT was 35 ± 7 min. Compared with the motion recorded on four-dimensional CT, the mean ΔM was 0.4, 1.0, and 0.4 mm, respectively, in the mediolateral, superior-inferior, and anterior-posterior directions. On treatment, the observed ΔM was, on average, <1 mm; no ΔM was statistically different with respect to the initial rcCBCT. However, patients in whom abdominal compression was used showed a statistically significant difference (p < 0.05) in the variance of ΔM with respect to the initial rcCBCT in the superior-inferior direction.
Conclusions
The inter- and intrafractional ΔM that occur during a course of lung SBRT are small. However, abdominal compression causes larger variations in the time spent on the treatment couch and in the inter- and intrafractional ΔM values.
∗Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Ontario, Canada
†Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
‡Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands
Reprint requests to: Jean-Pierre Bissonnette, Ph.D., Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Ontario, Canada. Tel: (416) 946-4501, ext. 2151; Fax: (416) 946-5655
This research was supported by the Addie MacNaughton Chair in Thoracic Radiation Oncology and by Elekta Oncology Systems. Kevin Franks, M.D., is the recipient of a grant from the Canadian Institute of Health Research (CIHR) Strategic Training Fellowship in the Excellence in Radiation Research for the 21st Century (EIRR21) program.
Conflict of interest: This research was supported in part by grants from Elekta Oncology Systems. The authors' institutions are members of the Elekta Synergy Research Group, together with the William Beaumont Hospital, Royal Oak, MI; Thomas Jefferson University, Philadelphia, PA; Christie Hospital, Manchester, UK; and Elekta Oncology Systems Ltd., Crawley, West Sussex, UK.
ABSTRACT