Risk factors for radiation pneumonitis caused by whole breast irradiation following breast-conserving surgery.

We evaluated risk factors of radiation pneumonitis (RP) after whole breast irradiation following breast-conserving surgery. Four hundred and seventy-two cases underwent whole breast irradiation with tangential field following breast-conserving surgery in our hospital, between January 2005 and April 2007. Of these cases, we performed statistical analyses for 423 breasts of 413 patients, using a pulmonary dose-volume histogram. Patient characteristics, treatment regimens and irradiation methods were included as variables in the analyses on risk factors of RP. As a result, 89 breasts of 84 cases (21%) were diagnosed with RP. The version 3.0 of the NCI Common Terminology Criteria for Adverse Events was used to evaluate the grade of pneumonitis: 77 cases (18.2%) were diagnosed as Grade 1 RP, 10 cases (2.3%) as Grade 2, and 2 cases (0.5%) as Grade 3. Multivariate analysis indicated that the significant risk factors for RP were central lung distance (CLD) (>1.8 cm) and the short axis length of the radiation field. The incidence of radiation-induced bronchiolitis obliterans organizing pneumonia (BOOP) syndrome significantly correlated only with CLD. The lung volume within the radiation field was shown to be a significant risk factor for RP and radiation-induced BOOP syndrome.