We investigated the factors predicting radiation-induced organizing pneumonia (RIOP) relapse\nafter tangential breast irradiation. The participants included 23 patients diagnosed with RIOP at\nthe St. Marianna University School of Medicine Hospital between January 2008 and March 2015.\nRelapse was defined as the appearance of new lesions on diagnostic images during follow-up or\nafter commencing treatment. The relapse-free survival rate and the following 9 parameters were\ncompared between patients with and without RIOP relapse: 1) age (less than vs. equal to or more\nthan the median); 2) white blood cell count (less than vs. equal to or more than the median); 3)\nC-reactive protein (CRP) level at the time of RIOP diagnosis (less than normal, more than normal/\nless than borderline, and more than borderline); 4) boost irradiation (yes vs. no); 5) maximum\nlung depth on linacgraphy (less than vs. equal to or more than the median); 6) hormone therapy\n(yes vs. no); 7) chemotherapy (yes vs. no); 8) RIOP ratio in the whole lung (less than vs. equal to or\nmore than the median) at the time of RIOP diagnosis; and 9) use of corticosteroids (yes vs. no). The\nKaplan-Meier method was used for statistical analysis, with relapse as the cutoff. The follow-up\nperiod spanned the date of RIOP onset to May 30, 2015. The level of significance for 2-sided tests\nwas p 0.05. Relapse was evident in 14 patients (60.8%). The relapse-free survival rate was significantly\ngreater in the normal CRP group (less than 0.30 mg/dl) than in the abnormal CRP group\n(more than 0.36 mg/dl) (p = 0.044) and in the normal/borderline CRP group (less than 0.36 mg/dl)\nthan in the high CRP group (more than 0.70 mg/dl) (p < 0.01). The CRP level at RIOP onset may be\na useful predictor of relapse after breast-conserving therapy.
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