ESTRO 2021 Abstract Book

S1505

ESTRO 2021

combination of T2-w and contrast-enhanced T1-w anatomic images were used to define regions-of-interest (ROI) as the dominant malignant nodules (DMNs) and the benign prostate (the entire prostate with the summed DMNs being subtracted). MRI textural radiomic features associated with prostate cancer response in the literature of energy and homogeneity were selected. Pyradiomics was used to extract textural features of the ROIs. For each ROI, a student paired t-test was used to compare mean feature values before and after androgen deprivation therapy. A p-value of < 0.01 was considered significant to account for multiple comparisons. Radiomic feature changes and dynamic MRI kinetic parameters were correlated using Pearson’s coefficient, r. Results For the 19 patients, the median time between the first baseline scan and the first on-treatment scan was 91.5 days (range 82-105). The median time between the first two scans was two days (range 1-8), and between the last two scans 1.5 days (range 1–14). Baseline homogeneity and energy values differed significantly between benign and malignant tissue ( p<0.0001 ). In response to nADT, homogeneity and energy showed reciprocal changes, significantly increased in benign prostate whilst decreasing in the DMN. Androgen deprivation induced an expected shrinkage in the volume of the prostate gland; reducing by an average of 14.4 mls (34.5%) after three months’ therapy. The reduction in tumour homogeneity and energy feature values showed a positive association with the decline in tumour blood flow and tumour blood volume induced by androgen deprivation as derived from dynamic MR imaging parameters; all r 0.69-0.78, all p<0.001.

Conclusion Energy and homogeneity radiomic features derived from MR images of benign and malignant prostate showed significant reciprocal changes in response to nADT. This study confirms the potential of these radiomic features to act as surrogate markers of tumour androgen sensitivity due to their strong association with ADT- induced physiological effects in prostate tumours. PO-1779 Endoscopically Determined Gross Tumor Volume and Metabolic Tumor Volume in Esophageal Cancer T.H. Lee 1 , H.G. Ryoo 2 , R. Lee 3 , J.C. Paeng 2 , H. Chung 4 , H.J. Kim 1 1 Seoul National University College of Medicine and Hospital, Department of Radiation Oncology, Seoul, Korea Republic of; 2 Seoul National University College of Medicine and Hospital, Department of Nuclear Medicine, Seoul, Korea Republic of; 3 Chung-Ang University Hospital, Department of Nuclear Medicine, Seoul, Korea Republic of; 4 Seoul National University College of Medicine and Hospital, Department of Internal Medicine and Liver Research Institute, Seoul, Korea Republic of Purpose or Objective The purpose of this study is to compare the longitudinal location of endoscopically-defined GTV and positron emission tomography-based metabolic tumor volume (MTV) of esophageal cancer. Materials and Methods A retrospective review of medical records was performed of the nine patients who underwent endoscopic placement of fiducial markers for radiotherapy of esophageal squamous cell carcinoma. Endoscopic hemoclips