Dosimetric Parameters Spontaneous Rib Fracture in Breast Cancer Patients Received Radiotherapy
Dowook Kim,
Korea Republic of
PO-1223
Abstract
Dosimetric Parameters Spontaneous Rib Fracture in Breast Cancer Patients Received Radiotherapy
Authors: Dowook Kim1, Jong Min Park2, Kyung Hwan Shin1
1Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 2Seoul National University, Department of Radiation Oncology, Seoul, Korea Republic of
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Purpose or Objective
Spontaneous rib fracture (SRF), a fracture that occurs without traumatic factors, is a relatively common late complication in treated breast cancer patients. This study evaluated the incidence and risk factors of ipsilateral SRF after radiotherapy (RT) in breast cancer patients based on bone scans. In addition, we identified dosimetric parameters that were significantly associated with ipsilateral SRF.
Material and Methods
We retrospectively reviewed 2,205 patients with breast cancer who underwent RT between 2014 and 2016, and who were followed up with at least three times bone scans. Among patients, 44.3% received the conventional fractionation scheme, and 55.7% received the hypofractionated scheme. The endpoint was ipsilateral SRF detected by bone scans. In this study, we used an electron beam for tumor bed boost and patients who received a boost were excluded from the dosimetric analysis. In the no boost group (n=539), all ipsilateral ribs were contoured to build the dose-volume histograms. All dosimetric parameters of ribs were calculated into the equivalent dose in 2 Gy fractions (EQD2) to correct for fractionation dose.
Results
The median follow-up duration was 41.0 months. Ipsilateral SRF occurred in 17.0% of patients during the follow-up. In multivariate analysis, abnormal bone density and hypofractionated RT were significant clinical risk factors for ipsilateral SRF (P = 0.019 and P < 0.001, respectively). The maximum dose (Dmax) EQD2 was the most significant dosimetric parameter associated with ipsilateral SRF. The 5-year incidence of ipsilateral SRF for Dmax more than and less than 53 Gy were 47.3% and 12.1% (P < 0.001), and for rib volume receiving 40 Gy (V40) more than and less than 23% were 30.9% and 24.5% (P = 0.01), respectively. Other dosimetric parameters, including mean dose EQD2 of ribs, V20, V30, and ipsilateral rib volume were not significantly different.
Conclusion
Dmax EQD2 was the most relevant dosimetric parameter that predict the ipsilateral SRF in RT-treated breast cancer patients. In particular, the incidence of Ipsilateral SRF showed the most significant difference when Dmax EQD2 > 53 Gy.