days respectively. Patients with an immune-related adverse event survived longer than patients with no immune-related adverse event, with a mean of 208 versus 88 days. CyTOF analysis showed patients with a systemic PR after SBRT had a population of CD8+ CD127- Ki-67+ CD45RO+ T cells that correlated with response. Conclusion: The addition of SBRT after progression on immunotherapy resulted in increased PFS, a systemic response rate of 9.52%, and a disease control rate of 57.14%. Improved PFS correlated with an increased TIL score, the presence of an immune-related adverse event, and T cell acti- vation status. Author Disclosure: A.M. Campbell: Employee; West Haven VA. W.L. Cai: None. D. Burkhardt: None. S.N. Gettinger: Research Grant; Gen- entech. Consultant; BMS, ARIAD, Alexion. S.B. Goldberg: Research Grant; Astrazeneca. Advisory Board; ER Squibb, Boehringer Ingelheim. M. Amodio: None. S. Kaech: Research Grant; Roche. S. Krishnaswamy: None. R.H. Decker: Research Grant; Merck & Co., Inc. Advisory Board; Astra Zeneca. 75 Pre-Treatment Circulating Tumor Cell Levels Correlate with Regional and Distant Failure Rates Following Stereotactic Body Radiation Therapy for Early Stage Non-Small Cell Lung Cancer M. Frick, 1 S.J. Feigenberg, 2 S. Jean-Baptiste, 1 L. Aguarin, 1 A. Mendes, 1 C. Chinniah, 1 S.D. Swisher-McClure, 1 S.M. Hahn, 3 K.A. Cengel, 1 A.T. Berman, 1 W.P. Levin, 1 J.F. Dorsey, 1 C.B. Simone, II, 4 and G.D. Kao 1 ; 1 Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 2 University of Pennsylvania, Philadelphia, PA, 3 The University of Texas MD Anderson Cancer Center, Houston, TX, 4 New York Proton Center, New York, NY Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) has become the standard of care for patients with medically inoperable early stage non-small cell lung cancer (NSCLC) due to good local control rates and minimal morbidity. However, of patients treated with SBRT, 10-15% patients fail regionally and 25% fail distantly. Our hypothesis underlying this prospective trial was that a high burden of circulating tumor cells (CTCs) prior to treatment is a useful prognostic marker for increased risk of recurrence following SBRT. Materials/Methods: 92 subjects with stage I NSCLC treated with SBRT were prospectively enrolled on an IRB-approved protocol. CTCs were enumerated by an assay utilizing a green fluorescent protein (GFP)- expressing adenoviral probe that detects the elevated telomerase activity in cancer cells. CTC “positivity” was defined as 1.3 GFP-positive cells per mL of peripheral blood samples. Pre-treatment samples were collected at the time of treatment consent for SBRT or at simulation. RT was delivered to a median dose of 50Gy (range, 40-60 Gy) in five fractions. Patient characteristics: female (58%), Caucasian (80%), and current (20%) or former (75%) smokers; median age was 71 years. Subjects had T1a (64%), T1b (23%), or T2a (13%) NSCLC with a median tumor size of 1.7 cm (range, 0.5-5.0 cm). Kaplan-Meier survival analysis and Cox multivariate regression analysis explored the relative effect of covariates on recurrence and survival outcomes, controlling for history of previous NSCLC, tumor size, and pre-treatment PET scan SUVmax. Receiver operating charac- teristic curves were generated for a series of baseline CTC values between 2 and 7 to identify if there were a threshold value prognostic of disease recurrence. Results: With a median follow-up of 24 months (range, 2-62 months), the 2-year local, regional and distant control rates were 90.0%, 86.4%, and 86.5%, respectively. 38 of 92 subjects (40%) had a positive CTC test prior to treatment. Overall, a positive CTC test when compared to a negative test was not associated with local, nodal, or distant recurrence. A pre-SBRT cutoff of 5 CTCs/mL demonstrated the maximal area under the cure in predicting any event of recurrence (AUCZ0.64, specificityZ90.4%), therein defining favorable (nZ78) and unfavorable (nZ14) prognostic groups by baseline CTC. Increased risk of nodal and distant failure was observed in the unfavorable versus favorable cohorts, with 2-year freedom from nodal and distant failure of 83.9% and 75.7% versus 86.7% (HR 3.92, pZ0.04) and 89.2%, (HR 4.29, pZ0.03). Conclusion: Higher pre-treatment CTC counts appears to be predictive of increased risks of regional and distant recurrences following SBRT for early stage NSCLC, thus potentially identifying the subset of patients at highest risk of regional and distant recurrences who could benefit most from intensified or adjuvant systemic therapy. Author Disclosure: M. Frick: None. S.J. Feigenberg: None. S. Jean- Baptiste: None. L. Aguarin: None. A. Mendes: None. C. Chinniah: None. S.D. Swisher-McClure: None. S.M. Hahn: None. K.A. Cengel: None. A.T. Berman: None. W.P. Levin: None. J.F. Dorsey: None. C.B. Simone: Employee; Nemours/Alfred I. duPont Hospital for Children; Proton Collaborative Group (PCG), Annals of Palliative Medicine, American Society for Radiation Oncology. G.D. Kao: Salary; University of Pennsylvania. 76 Intensity Modulated Radiotherapy Plus Etoposide/Cisplatin Chemotherapy for Patients with Unresectable Thymic Epithelial Tumors: A Prospective Phase II Study F. Xingwen, 1 K. Wu, 2 and Y. Yang 1 ; 1 Shanghai Cancer Center, Fudan University, shanghai, China, 2 Fudan University Shanghai Cancer Center, Shanghai, China Purpose/Objective(s): To evaluate the efficacy and safety of intensity modulated radiotherapy (IMRT) plus etoposide/cisplatin (EP) for patients with unresectable thymic epithelial tumors (TETs). Materials/Methods: In this open-label, single-arm, phase II trial, patients with untreated and unresectable TETs were treated with IMRT and EP. Two cycles of EP (etoposide 75mg/m 2 and cisplatin 25 mg/m 2 , on day 1 to 3, every 4 weeks) were given concurrent with radiotherapy of 60 Gy, and then another two cycles were given after radiotherapy. The primary endpoint was objective response rates (ORRs). The seconded endpoints were progression free survival (PFS), overall survival (OS) and toxicity. Results: A total of 56 patients were enrolled and analyzed from June 2011 to May 2018. Twenty-two patients had thymoma and 34 patients had thymic carcinoma (TC). The median age was 52 years (range, 21 to 76 years), and 30 patients (53.6%) were male. Eight patients (14.3%) were stage IIIB, 6 patients (10.7%) were stage IVA, and 42 patients (75.0%) were stage IVB according to Masaoka-Koga staging system. The ORRs were 85.7% (95% CI: 76.3% to 95.2%). With a median follow-up of 30 months (range: 7 to 91 months), the 1-year, 2-year and 5-year PFS and OS was 65.9%, 49.7%, and 30.9%, and 90.8%, 76.3% and 68.1%, respectively. The treatment was well tolerated. The major grade 3-4 adverse event was leukopenia in 24 (42.9%) patients. Conclusion: IMRT plus EP demonstrated high ORRs for advanced unre- sectable TETs safely. The 5-year OS of 68.1% was promising. A ran- domized phase III study to compare this strategy with chemotherapy alone for advanced unresectable TETs is warranted. Author Disclosure: F. Xingwen: None. K. Wu: None. Y. Yang: None. 77 A Phase III Multi-Centre Randomised Trial comparing adjuvant versus early salvage Radiotherapy following a Radical Prostatectomy: Results of the TROG 08.03 and ANZUP “RAVES” Trial A. Kneebone, 1 , 2 C. Fraser-Browne, 3 W. Delprado, 4,5 G. Duchesne, 6,7 R. Fisher, 8 M. Frydenberg, 9 A. Haworth, 10 A. Herschtal, 11 D.J. Joseph, 12,13 T.S. Lim, 14 J.M. Martin, 15 J.L. Millar, 16,17 M. Sidhom, 18 N. Spry, 19 C.I. Tang, 19 S. Turner, 20,21 S.G. Williams, 8 K.L. Wiltshire, 22 H. Woo, 23 and M. Pearse 3 ; 1 Royal North Shore Hospital, Sydney, Australia, 2 University of Sydney, Sydney, Australia, 3 Auckland Hospital, Auckland, New Zealand, 4 Douglass Hanly Moir Pathology, Sydney, Australia, 5 University of Notre Dame Australia, Freemantle, Australia, 6 Sir Peter MacCallum Department of Oncology, Melbourne, Australia, 7 University of Volume 105  Number 1S  Supplement 2019 Oral Scientific Sessions S37