the PR group. The total concentration changes of ctDNA before and after radiotherapy was not related to the response rate (0.023, P>0.05). The number of copies with EGFR changes was correlated to the response rate (0.65, P Z 0.01), there are significant differences between the PR and SD groups of the number of copies with EGFR changes before and after radiotherapy (P Z 0.02). Conclusion: The copies of EGFR in ctDNA decreased during radiotherapy. The changes correlated with better efficacy in subsequent evaluation. It suggesting that quantification of EGFR in ctDNA is expected to be a new molecular biological marker for the efficacy of radiotherapy for NSCLC that deserves further investigation.

treatment was compared using clonogenic cell survival assay when protons were delivered with doses of 2, 4 and 6 Gy at the mid-spread out Bragg peak (SOBP) using a reference beam of 15 g/cm 2 range and 10 g/ cm 2 modulation. Involvement of the DNA damage response was assessed by western blot analysis for DNA repair proteins and immunofluorescence staining for g-H2AX foci. Results: Rad51 depletion by siRNA sensitized H1299 and A549 cells to protons and photons. However, both H1299 and A549 cell lines were significantly more sensitive to proton irradiation compared to photon. Survival fraction at 2 Gy (SF2) for H1299 cells exposed to proton beam was reduced from (53.7 AE 0.49) % in siScr to (21.8 AE 2.28) % in siRad51treated group. Similarly, SF2 for A549 cells was reduced from (59.1 AE 1.16) % in siScr to (29.6 AE 4.9) % following siRad51-treatment. Survival enhancement ratios (SER) were calculated at 10% cell survival by dividing proton radiation dose of the siScr to that of siRad51 for that survival. The SER for H1299 cells at 10% survival was 1.9 and for A549 was 1.33, respectively. Similar results were obtained with the Rad51 small molecule inhibitor, BO2. Our results reveal that this enhanced efficacy of protons is associated with increased ATM and Chk1 phosphorylation as well as increased H2AX phosphorylation. Further, Rad51 knockdown led to persistent radiation-induced DNA damage as reflected by g-H2AX foci staining. Conclusion: Our results demonstrate that Rad51 inhibition significantly increased the radiosensitivity of NSCLC cells, and that this increased radiosensitivity was mediated by the suppression of DNA repair. The effect of siRad51 on radiosensitization to protons was more significant than to photons.Purpose/Objective(s): Neuroendocrine (NE) malignancies are a heterogeneous group of neoplasms that include carcinoid, islet cell tumors, and medullary thyroid cancers. Patients with NE cancer often present with liver metastasis, which portend a dismal survival rate and cause debilitating symptoms. In addition to the lack of guidelines for radiation and chemotherapy, there is a current deficiency in experimental tools to predict clinical response; there are very few human-derived NE cancer cell lines and establishing patient-derived xenografts (PDX) for this disease proved nearly impossible. To overcome these limitations, we propose to employ a Volume 99 Number 2S Supplement 2017 Poster Viewing E597