Purpose/Objective(s): Although most radiation treatment is planned on a routine basis, there are several urgent indications for emergent treatment. Patients receiving emergent treatment are typically sicker and more advanced in their disease course. The primary objective of this study was to characterize a cohort of patients treated emergently with radiation, including both inpatients and outpatients, and to report on outcomes and predictors of survival. Materials/Methods: All patients treated emergently within a single insti- tution were identified by querying the treatment database for urgent simulation requisition orders during the 2014 calendar year. All treatment sites and fractionation schedules were included. Data recorded included demographic information, performance status, indication for urgent radi- ation, primary disease site, inpatient status, whether the patient completed the course of therapy, and whether palliative care was involved at time of treatment. All statistical analyses (Kaplan-Meier curves, chi-square ana- lyses) were completed in SAS. Results: Overall, 214 patients (with a combined total of 238 courses) underwent emergent treatment in 2014. Of the total courses, 44% (105) occurred while patients were hospitalized. Bone metastases were more commonly treated as an outpatient (P < 0.0001), while cord compression, leptomeningeal disease, and bleeding were more commonly treated on an inpatient basis (P < 0.05). Palliative care was more likely to be involved for inpatients (P Z 0.0008). Overall, 22% (23) of inpatients stopped treatment early, compared to 13% (17) of outpatients (P Z 0.06). In- patients had a significantly shorter survival compared to outpatients (2 months vs. 6 months; P < 0.0001), despite both groups being treated ur- gently. Both groups had an average of 8.4 fractions planned (range, 1-30; standard deviation 5.2). Conclusion: Patients treated urgently have a notably poor survival and a substantial proportion do not complete treatment. Inpatients do particularly poorly, with a shorter survival compared to outpatients also treated for urgent indications. Inpatients appear to be less likely to complete treatment than outpatients. Given the number of inpatients who discontinue treatment before receiving significant benefit and their particularly poor prognosis, shorter fractionation schemes may be warranted. Author Disclosure: S.A. Dudley: None. S. Aggarwal: None. M.M. Grade: None. K.A. Kumar: None. B.E. Turner: None. Y. Liu: None. R. Von Eyben: None. D.T. Chang: Research Grant; Varian Medical Systems. Honoraria; Varian Medical Systems. Stock; ViewRay. S.J. Knox: None. 1117 Fiducial Markers are Necessary for Accurate Delivery of Liver SBRT T.P. Robin, B.L. Jones, and K.A. Goodman; Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, CO Purpose/Objective(s): We standardly use fiducial markers for target localization when administering liver stereotactic body radiation therapy (SBRT). However, there are few data demonstrating the impact of matching to fiducials on accuracy of liver SBRT delivery. Given the risks of percutaneous placement of fiducials, the aim of our study was to evaluate the benefit of fiducial-based SBRT and to potentially define a subset of patients that can be treated without fiducial markers. Materials/Methods: Nineteen metastatic (n Z 15) and primary (n Z 4) liver tumors were treated with SBRT. Doses ranged from 30-54 Gy in 3-5 fractions, and 75 individual fractions were delivered in total. Target localization at the time of treatment was performed using fiducial markers on cone beam computed tomography (CBCT). To assess the difference between fiducial-based and non-fiducial based set-up, each CBCT was then retrospectively realigned to best match the liver edge. The fiducial marker position was considered the gold standard. Shifts from the fiducial to liver edge alignment were recorded and an absolute Cartesian shift was calcu- lated. To predict the dosimetric impact of these position errors, an artificial neural network was used to model the dose in the vicinity of the tumor. Results: When aligning to the liver edge, the mean absolute Cartesian shift from fiducial alignment was 4.5 mm (0.73 e 13.3 mm). The lateral, lon- gitudinal, and vertical shifts, were randomly distributed with mean values of 0.19 mm (-5.9 e 8.2 mm), -0.23 mm (-10.5 e 8.8 mm), and 0.43 mm (-9.0 e 8.4 mm), respectively. Thirty-three percent of fractions were found to have an absolute shift greater than 5 mm [our standard planning target volume (PTV) expansion] and 63% of patients had at least one absolute shift greater than 5 mm. In the neural network dose model, a 5 mm shift was associated with a dose reduction of 18.5% + 2.5%. The maximum shift seen was 13.3 mm which was associated with a projected target dose reduction of 45.0% + 5.6%. There were no tumor factors (including tumor size, distance from liver edge to the tumor, and distance from the tumor to the liver dome) that had a statistically significant correlation with worse alignment when matching to the liver edge without fiducials. Conclusion: Our findings demonstrate that treatment set-up without fidu- cial markers in liver SBRT leads to a mean positional error of 4.5 mm as compared to fiducial-based set-up. In one third of treatments, this variation was greater than our standard PTV expansion and would result in a sub- stantial decrease in delivered dose. We were unable to define a subset of patients where fiducial markers may not be necessary. While these data suggest that with current technology, fiducial markers are necessary for the accurate delivery of liver SBRT; further work is needed to improve on- board imaging and localization techniques to allow for fiducial-less liver SBRT. Author Disclosure: T.P. Robin: None. B.L. Jones: None. K.A. Goodman: None. 1118 Initial Clinical Experience with Using an Automated Dose Tracking Tool to Verify Dose Delivery and Trigger Adaptive Replanning K. Kainz, 1 S.N. LIM, 1 G.P. Chen, 1 C.A.F. Lawton, 2 M.L. Siker, 1 S. Firat, 1 J.R. Robbins, 1 B.A. Erickson, 3 and A. Li 1 ; 1 Medical College of Wisconsin, Milwaukee, WI, 2 Medical College of Wisconsin Department of Radiation Oncology, Milwaukee, WI, 3 Medical College of Wisconsin Department of Radiation Oncology and Clement J Zablocki VA Medical Center, Milwaukee, WI Purpose/Objective(s): We report on our initial clinical use of an auto- mated software tool which incorporates deformable registration and dose summation to identify and track inter-fraction anatomic changes and delivered doses based upon daily MVCT. We used this tool to verify dose delivery and to trigger adaptive replanning. Materials/Methods: For the first 32 patients (12 male pelvis, 9 female pelvis, 8 head and neck, 3 pediatric) treated on our helical tomotherapy system, daily MVCT IGRT images and MVCT-to-plan-CT shift informa- tion were input to the dose-tracking software tool. For each fraction, the tool calculates a deformable registration map to warp each region-of-in- terest (ROI) from the planning CT to the daily MVCT, and recalculates the “delivered” dose on the MVCT based on the planned beam configuration (sinogram). Changes to the ROI volumes and dose for each fraction are tracked, and the dose distribution is summed for all fractions to date. The planned DVH is compared with the delivered DVH in terms of accumu- lated dose for all fractions delivered to date, as well as projected dose (which assumes that the dose distribution for the most-recent fraction applies to the remaining fractions). The tool also enables review of image registration, ROI deformation, and dose recalculation for each fraction. Aside from initial enrollment of the patient’s plan within the software tool, no further user intervention is required. Results: Tests of the software tool upon a cylindrical solid-water phantom demonstrated that the MVCT-based dose distributions are consistent with the planned dose to within 1%. For several delivered pelvic radiotherapy plans, review of the ROIs and delivered dose distribution on the daily MVCT verified that the CTV coverage was achieved for each fraction, although for some fractions underdosing of the peripheral PTV was observed and confirmed by the accumulated DVH comparison with the plan. PTV underdosing was attributed to PTV warping uncertainties due to its location within soft tissue not bordering obvious anatomic landmarks, or (as in the case of one prostate patient) to anatomic changes within the patient such as a 1 to 2 cm increase of the anterior extent. For one head and neck patient, for whom weight loss was suspected due to degraded fit of International Journal of Radiation Oncology  Biology  Physics S222