title: Dosemetric Parameters Predictive of Rib Fractures after Proton Beam Therapy for Early-Stage Lung Cancer.
abstract: Proton beam therapy (PBT) is the preferred modality for early-stage lung cancer. Compared with X-ray therapy, PBT offers good dose concentration as revealed by the characteristics of the Bragg peak. Rib fractures (RFs) after PBT lead to decreased quality of life for patients. However, the incidence of and the risk factors for RFs after PBT have not yet been clarified. We therefore explored the relationship between irradiated rib volume and RFs after PBT for early-stage lung cancer. The purpose of this study was to investigate the incidence and the risk factors for RFs following PBT for early-stage lung cancer. We investigated 52 early-stage lung cancer patients and analyzed a total of 215 irradiated ribs after PBT. Grade 2 RFs occurred in 12 patients (20 ribs); these RFs were symptomatic without displacement. No patient experienced more severe RFs. The median time to grade 2 RFs development was 17 months (range: 9-29 months). The three-year incidence of grade 2 RFs was 30.2%. According to the analysis comparing radiation dose and rib volume using receiver operating characteristic curves, we demonstrated that the volume of ribs receiving more than 120 Gy3 (relative biological effectiveness (RBE)) was more than 3.7 cm(3) at an area under the curve of 0.81, which increased the incidence of RFs after PBT (P < 0.001). In this study, RFs were frequently observed following PBT for early-stage lung cancer. We demonstrated that the volume of ribs receiving more than 120 Gy3 (RBE) was the most significant parameter for predicting RFs.
authors.affiliation: Department of Radiation Oncology, Tohoku University Graduate School of Medicine.
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Nakamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kato
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kadoya
authors.forename: Motohisa
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Azami
authors.forename: Masato
authors.initials: M
authors.lastname: Hareyama
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kikuchi
authors.forename: Keiichi
authors.initials: K
authors.lastname: Jingu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D061766:Proton Therapy / Q000009:adverse effects*; D012253:Rib Fractures / Q000209:etiology*