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Updated: May 13, 2025
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Risk factors for radiation-induced rib fractures following proton beam therapy for stage I non-small cell lung
Naoaki Kondo1, Takashi Yoshiura2, Yasumasa Kakinohana3
1Department of Radiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1, Sakuragaoka, Kagoshima, Japan. kondonaoaki@gmail.com.
Background:
Understanding and managing radiation-induced adverse events is becoming increasingly important in hypofractionated radiotherapy due to the use of higher doses per fraction compared with conventional radiotherapy. Specifically, toxicities of hypofractionated proton and carbon-ion beam therapy are still unclear. We investigated the clinical, anatomical, and dosimetric risk factors for radiation-induced rib fractures (RIRFs) following passive-scattering proton beam therapy (PBT) for stage I non-small cell lung cancer (NSCLC).
Methods:
We retrospectively investigated patients with stage I NSCLC who underwent PBT with 66-70 Gy (relative biological effectiveness [RBE]) in 10 fractions, completing a minimum follow-up of 36 months. Rib fractures were detected by follow-up chest computed tomography (CT) examination, independent of symptoms of thoracic pain. Dose-volume histograms of separately contoured ribs on planning CT images were calculated by the treatment planning system in a retrospective manner. Kaplan-Meier and Cox proportional hazards analyses were performed on individual ribs to identify significant risk factors associated with RIRF.
Results:
Among the 85 patients finally involved in this study, we identified 116 fractured ribs in 55 participants (64.7%). The 2- and 3-year frequencies of experiencing any RIRF were 36.5% and 52.9%, respectively. The median time-to-fracture was 23.5 months (range: 5-65). We used a total of 224 ribs irradiated over 50 Gy (RBE)-including all the detected fractured ribs-for statistical analysis. Univariate and multivariate analyses revealed the maximum-rib dose to a small volume, position of the maximum-dose point, bone mineral density, 1st rib number, and use of systemic corticosteroids to be related to the incidence of RIRFs.
Conclusions:
In addition to dosimetric parameters, factors related to skeletal structure and bone strength are crucial predictors of proton RIRFs and should be considered for safer radiation therapy.
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