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 Gy 3 (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 Gy 3 (RBE) was the most significant parameter for predicting RFs.

Hypofractionated proton therapy for non-small cell lung cancer: Ready for prime time? A systematic review and meta-analysis

“…Overall, the risk of developing a RF in patients receiving PBT for NSCLC has not been extensively investigated so far. The most comprehensive report has been provided by Ishikawa et al, who analyzed the dosimetric parameters predictive of RF in a cohort of 52 early-stage NSCLC patients with predominantly peripherally-located lesions (41/52, 79%) [62]. Specifically, the authors identified that the incidence of a grade 2 event was significantly increased if a rib volume greater than 3.7 cm3 received more than 120 Gy(RBE), with an α/β=3 Gy (p< 0.001), and a median time-to-event of 17 (range: 9-29) months.…”

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

“…To prevent rib fracture, dose-volume analysis may be useful. Many studies have performed dose-volume analyses of the relation between rib fracture and SBRT and proton therapy [ 17 , 18 , 23 , 24 , 25 , 26 ]. Asai et al .…”