BACKGROUND: Stereotactic body radiotherapy (SBRT) is a technique used to deliver high, ablative doses of radiation in a limited number of fractions to !1 extracranial target(s). To the authors' knowledge, the prevalence of SBRT use among radiation oncologists in the United States is unknown. METHODS: A random sample of 1600 American radiation oncologists was surveyed via e-mail and facsimile (fax) regarding SBRT usage, including year of adoption, motivations, disease sites treated, and common prescriptions used. RESULTS: Of 1373 contactable physicians, 551 responses (40.1%) were received. The percentage of physicians using SBRT was 63.9% (95% confidence interval, 60%-68%), of whom nearly half adopted it in 2008 or later. The most commonly cited reasons for adopting SBRT were to allow the delivery of higher than conventional radiation doses (90.3%) and to allow retreatment (73.9%) in select patients. Academic physicians were more likely to report research as a motivation for SBRT adoption, whereas physicians in private practice were more likely to list competitive reasons. Among SBRT users, the most common disease sites treated were lung (89.3%), spine (67.5%), and liver (54.5%) tumors. Overall, 76.0% of current SBRT users planned to increase their use, whereas 66.5% of nonusers planned to adopt the technology in the future. CONCLUSIONS: SBRT has rapidly become a widely adopted treatment approach among American radiation oncologists. Further research and prospective trials are necessary to assess the benefits and risks of this novel technology.

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Algorithms for direct tumor tracking in rotational cone-beam projections and for reconstruction of phase-binned 3D tumor trajectories were developed. The feasibility of the algorithm was demonstrated on a digital phantom, a physical phantom and two patients. Tracking results were obtained by comparing reference templates generated from 4DCT to rotational cone-beam projections. The 95th percentile absolute errors (e(95)) in phantom tracking results did not exceed 1.7 mm in either imager dimension, while e(95) in the patients was 3.3 mm or less. Accurate phase-binned trajectories were reconstructed in each case, with 3D maximum errors of no more than 1.0 mm in the phantoms and 2.0 mm in the patients. This work shows the feasibility of a direct tumor tracking technique for rotational images, and demonstrates that an accurate 3D tumor trajectory can be reconstructed from relatively less accurate tracking results. The ability to reconstruct the tumor's average trajectory from a 3D cone-beam CT scan on the day of treatment could allow for better patient setup and quality assurance, while direct tumor tracking in rotational projections could be clinically useful for rotational therapy such as volumetric modulated arc therapy (VMAT).