Long-term risk of hip complications after radiotherapy for prostate cancer - A dose-response study

Abstract Purpose The aim of the present study was to analyze the long-term incidence of hip complications, after external beam radiotherapy (EBRT), compared to age-matched controls from the general population. We also investigated whether there were any dose−response associations. Methods and material 349 patients with prostate cancer treated to curative dose with EBRT during 1997-2002 were included in the study. Physical and fractionation-corrected dose-volume descriptors were derived for the femoral heads, pubic bone and sacrum. Information on skeletal events was collected for the patients and 1661 matched controls through the Prostate Cancer data Base XXXXXX (PCBaSe). Uni- and multivariable Cox proportional hazard regression was used to analyze time to events. Results Data from 346 patients were available for analysis. The median mean physical dose and the corresponding equivalent 2-Gy/fraction dose to the femoral heads were Dmean = 35.5 Gy and EQD2mean = 28.7 Gy, respectively. The median follow-up time was 16.0 years. During the follow-up 12 hip fractures occurred. Hip osteoarthritis was diagnosed in 36 cases, 29 cases leading to replacement surgery. No increased risk of hip fractures was found. Hip osteoarthritis was the only event for which a statistically significant difference was found between the irradiated cohort and the controls (cause-specific hazard ratio of 1.56 (95% CI: 1.07-2.26, p=0.02)). The cumulative incidence of osteoarthrosis at 10 years was 8.1% and 4.9% in the irradiated cohort and the controls, respectively. A significant relationship between osteoarthritis and the volume of the femoral head receiving ≥40 Gy (EQD2), was found. Conclusions In this study of 346 patients treated with conventional radiotherapy we found no increased risk of hip fracture but an increased risk of clinically relevant osteoarthritis at long-term follow-up. Our results indicate a dose response relationship between osteoarthritis and the volume of the femoral head receiving an EQD2 dose of ≥40 Gy.