1. 3. Results (continued) Of single fraction regimens, 87% prescribed ≥16 Gy. Single fraction treatments were constrained by maximum spinal cord doses of ≤14 Gy and ≤10 Gy by 91% and 61% of respondents, respectively. Respondents were more likely to treat with 1 fraction in large practices (≥7 radiation oncologists) (74% vs 47%, p<0.001). Practice type, years of experience, use of fiducial markers and body frame, and target localization techniques were not associated with significant differences in fractionation. The median dose per fraction among all prescriptions was 16 Gy. Fraction sizes of ≥16 Gy were all delivered as single fraction regimens and were more common in large practices (65% vs 40%, p=0.002) and among physicians who have treated >10 spine SBRT patients (59% vs 41%, p=0.02). Of spine SBRT users, only 12% reported routine usage of fiducial markers, which was associated with the use of a body frame (r s =0.14, p<0.05) by rank correlation. A Survey of Spine Stereotactic Body Radiation Therapy (SBRT) Practice Patterns in the United States Hubert Pan, Brent S Rose, Daniel R Simpson, Loren K Mell, Arno J Mundt, Joshua D Lawson University of California San Diego, Department of Radiation Oncology, La Jolla, CA 2. Materials/Methods A random sample of 1600 US radiation oncologists was surveyed from July to September 2010 regarding SBRT usage. Physicians were asked about their practice (type, size, location), years in practice, years of SBRT experience, use of fiducial markers and body frame, target localization techniques, maximum spinal cord dose, and most common prescription. Chi- square tests were performed to identify differences in fractionation and dose per fraction. Spearman’s rank correlation coefficients (r s ) were calculated to identify associations with fiducial marker usage. 4. Conclusions: The majority of spine SBRT users deliver treatment in a single fraction. This was more common in large practices (≥7 radiation oncologists). Among single fraction regimens, almost all respondents reported spinal cord tolerance within the RTOG guideline of 14 Gy, but over one third of respondents exceeded the 10 Gy recommended in a recent study to prevent radiation-induced myelopathy. Further study is required to ascertain the optimal tumor dosage and acceptable spinal cord tolerance in spine SBRT. 1. Purpose/Objectives Although stereotactic body radiation therapy (SBRT) offers promising results in spine tumors, little is known about its use in clinical practice. We thus conducted a nationwide survey of radiation oncologists in the United States, with results regarding overall SBRT adoption reported elsewhere (Pan et al, Cancer 2011). We present here further analysis, with a focus on clinical practice patterns, including prescriptions, fractionation, and fiducial marker usage in spine SBRT. 3. Results Of the 1600 physicians surveyed, 40% of contactable physicians responded; 64% of evaluable respondents used SBRT, of which 68% treated spine. Of spine SBRT users, 168 (81%) supplied their most common prescription. Most prescriptions were delivered over 1 (57%), 3 (22%) or 5 (18%) fractions. Figure 1. Bubble chart of the most common spine SBRT prescriptions. The size of the bubble corresponds to the number of responses. The largest bubbles reflect prescriptions of 18 Gy x 1 (22%), 16 Gy x 1 (20%), 8 Gy x 3 (11%), and 6 Gy x 5 (11%). Figure 2. Histogram of prescription dose for single fraction regimens of spine SBRT. Figure 3. Histogram of spinal cord tolerance for single fraction regimens of spine SBRT. Figure 4. Factors significantly associated with high-dose single fraction spine SBRT regimens by Chi-square testing.