- Tomé, Wolfgang A; Hodge, C Wesley; Mehta, Minesh P; Bentzen, Søren M
- Purpose/Objectives:Late complications of SBRT include radiation related rib fractures. We estimate the incidence of rib fracturesas a function of maximum absorbed rib dose after stereotactic body radiotherapy (SBRT) for early stage lung cancer. Materials/Methods:Of 23 patients treated with image guided SBRT (60 Gy in 5 fractions) between 2003 and 2006, 4 developed pathological rib fractures near the SBRT planning target volume (PTV). Both planned maximum dose and maximum Fraction-size equivalent dose (FED) to the combined rib volume lying within the prescription isodose volume was determined and a probit dose response model was fitted to the observed rib fracture data for each. Results:17 patients were evaluated, all with a minimum of 15 months follow-up. Median followup was 43 months (range 15-60 months). The median time to rib fracture was 26.5 months (range 15-34 months). The maximum rib dose ranged from 23.8-74.7 Gy (median 57.8 Gy) in 5 fractions. Dose was a significant predictor of rib fracture (p=0.02), with a D50 (123FED50) estimate of 66.71 Gy (73.52 Gy). The steepness of the dose-response curve was quantified by the m and γ50 value, estimated at m = 0.1663 and γ50 = 2.39 for the maximum dose probit dose response model and at m = 0.2747 and γ50 = 1.45 for the maximum 123FED50 probit dose response model. Conclusions:Maximum rib dose should be carefully considered in SBRT with appropriate risk counseling of patients whose maximum rib dose exceeds a dose of 50 Gy in 5 fractions or a maximum 123FED50 of 43.1 Gy, estimated to be associated with a 6.6 % risk of rib fractures. Hence, the inclusion of ribs as an "organ at risk" in intensity modulated radiotherapy (IMRT) planning should be considered as a way to reduce the likelihood of rib fractures.
- January 1, 2011
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