To investigate the tradeoff of esophageal treatment between real-time breath hold (BH) MR-guided radiotherapy (MRgRT), free breathing (FB) CT-based intensity modulated proton therapy (IMPT), and FB VMAT. We hypothesize that improved cardiopulmonary sparing would be achieved with BH MRgRT or FB IMPT compared to FB VMAT. Materials/Methods: We retrospectively evaluated differences in heart/lung dose and treatment plan conformality among 28 patients with distal esophageal cancer who were each treated with either IMPT (n Z 10), MRgRT on an MR-guided Linac (n Z 11), or VMAT (n Z 7). All were prescribed 50.4 Gy/28 fractions. IMPT and VMAT patients received a 4DCT simulation scan to quantify the internal target volume margin (ITV) for respiratory motion. MRgRT patients were simulated and treated in an inspiration BH with a 3 mm CTV to PTV margin. In lieu of a PTV margin for IMPT cases, robust optimization for range and setup uncertainty was performed on iCTV (i.e., CTV with respiratory ITV). RTOG plan quality metrics were used to evaluate target coverage (TC) (PTV V100%/PTV vol), homogeneity index (HI) (PTV D2%/ D98%), high dose conformity (PITV), low dose conformity (D2cm), and gradient (R50%). For all coverage metrics, the CTV was used. Results: Mean cardiac sparing among all patients between respective

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e14675 Background: This exploratory study assessed the ability of diffusion weighted MRI imaging in identifying small liver metastases as compared to F18- FDG PETCT. Methods: Patients with diagnosis of carcinoma of breast, lung, colorectal, pancreas, neuroendocrine and HCC who were staged for their disease using PET CT and MRI were included in the study. We randomly analyzed and compared PETCT and MRI images of 40 patients with hepatic metastases for sensitivity in detection of metastatic lesions in the liver on PETCT and MRI. Where possible, biopsy was performed if MRI/PET CT showed one or two small lesions in the liver. We performed ANCOVA to detect differences between PETCT and MRI controlling for primary sites of disease as a covariate. Results: The mean number of small lesions detected on PETCT was 0.92 where as it was 3.96 in MRI. There was a significant increase in small (p=0.02) and total number of lesions (p=0.01) seen on MRI compared to PET CT but not in large lesions. MRI was able to detect subcentimeter lesions more accurately than PET CT. Random biopsies done on small lesions found on MRI were positive for disease. MRI was able to detect small subcentimeter lesions three times more accurately than PET CT. Conclusions: MR diffusion is more sensitive in indentifying subcentimeter metastatic deposits in the liver that could help in accurate staging when PET CT is negative for liver metastases or when locoregional treatment for oligometastases is contemplated. However, pixels of DWI MRI (like reduced Signal to noise ratio at high b value, artefacts at liver edges and left lobe due to exaggerated susceptibility weighting and spin dephasing) need to be addressed by using other morphological images.

e14721 Background: In patients with Locally advanced/metastatic HCC, the median survival is 3 months. Most of these patients have altered liver functions which makes them unsuitable for any therapy. In this exploratory study we aim to test the effectiveness of I-131-lipiodol in prolonging survival in these patients. Methods: 15 patients with locally advanced HCC (unresectable) and metastatic HCC with altered liver functions (CHILDS B and C) were given I-131-lipiodol. Patients had received prior chemotherapy, prior TACE therapy, prior sorafenib and had treatment refractory progressive disease. We compared effects of I-131-Lipiodol in prolonging survival beyond three months in these patients. We performed a non parametric one sample kolmogorov Smirnov test comparing survival with I-131-lipiodol to an average 90 days survival reported in patients with advanced HCC. Results: Survival ranged from 46 to 417 days with a median survival of 144 days. However one sample test showed significant improvement in survival with I-131-lipiodol therapy compared to standard of care (z = 1.4, p = 0.04). Conclusions: I-131-lipiodol is a useful local therapy in management of patients with advanced HCC, randomized controlled trials are needed to validate its findings in adjuvant and palliative settings.