Femoral Fracture in Primary Soft Tissue Sarcoma Treated with Intensity-Modulated Radiation Therapy with and Without Dose Constraints.

Background: We previously reported that the cumulative risk of femoral fracture in patients treated with intensity-modulated radiation therapy (IMRT) for thigh and groin soft tissue sarcoma (STS) is low. In the current study, we sought to evaluate the effect of radiation dose constraints on the rate of femoral fracture in a more contemporary cohort.

Methods: All patients treated with IMRT for STS of the thigh or groin from 2004 to 2016 were included (n = 145). Beginning in 2011, radiation dose was constrained to a mean dose of < 37 Gy, volume of bone receiving ≥ 40 Gy (V40Gy) < 64%, and maximum dose < 59 Gy to limit the dose to the femur.

Results: Sixty-one patients were treated before dose constraints were implemented, and 84 patients were treated after. Median follow-up for patients treated before and after constraints were implemented was 6.1 and 5.7 years, respectively, and the two groups were demographically and clinically similar. On univariate analysis, the 5-year cumulative incidence of femoral fracture among patients treated with and without dose constraints was 1.8% (95% confidence interval [CI] 0.3-12.2%) versus 7.4% (95% CI 3.1-17.6%) [p = 0.11, p = non-significant, respectively]. On multivariable analysis, only age  ≥ 60 years was significantly associated with increased risk of fracture.

Conclusions: The risk of femoral fracture after IMRT for STS of the thigh/groin is low, and with the implementation of radiation dose constraints, the risk is < 2%. Although longer follow-up is needed, our results support the utilization of extremity sarcoma IMRT-specific dose constraints for fracture prevention.