Femoral Head And Neck

The radiation tolerance of the femoral head and neck is substantially lower than the radiation tolerance of long bones. This complication is increasingly rare as routine pelvic fields include blocking of the femoral neck and most of the femoral heads (Figure 1). If the inguinal nodes must be treated, the femoral head and neck will unavoidably receive a substantial radiation dose, and care must be taken not to exceed the radiation tolerance of these structures.

Pelvic Field
Figure 1. Pelvic field with femoral heads blocked.

Grigsby et al. reported on 207 patients who received groin irradiation as a component of pelvic irradiation for advanced or recurrent cancers of the vagina, vulva cervix, and endometrium.27 Most of the patients' groins were irradiated as part of the primary photon field, prescribed to midplane; 71 patients received groin boosts, most with high-energy photons. The incidence of femoral neck fracture was 4.8%; 40% of those patients with femoral neck fracture had fractures bilaterally. The actuarial cumulative incidence of fracture was 11% at 5 years, and 15% at 10 years (the authors describe these actuarial incidences as "excessive"). Mean doses were 52 Gy in those patients with fractures, and 47.6 Gy in those without. Irradiation dose was not a significant predictor of fracture, though there were no fractures with femoral neck doses below 42 Gy. Cigarette use correlated with the likelihood of femoral neck fracture (P = 0.027); there was also a correlation with radiologically confirmed pre-irradiation osteoporosis which approached statistical significance ( P = 0.068). With an absence of fractures below 42 Gy, these data would suggest that the TD 5/5 of the femoral neck is between 42 and 52 Gy.

C1. Therapy

Again, the best "therapy" for femoral head and neck fractures is prevention. Unless the femoral head/neck must be in the treatment field to encompass the PTV, they should be blocked. It is acceptable to include the most medial aspect of the femoral heads in order to adequately cover the pelvic lymph nodes at risk. If the femoral heads or necks must be treated, careful attention should be paid to keeping doses to these sensitive structures as low as possible.

Surgical repair of femoral head/neck fractures following radiotherapy may require special mechanical reinforcement due to the poor quality of bone following irradiation. In a retrospective study of 71 total hip replacements for complications following pelvic irradiation, the authors found a higher than typical post-replacement failure rate.28 When

Table 6. Risk factors for osteoporotic fracture32 and osteonecrosis

Low body weight (<58 kg)

Systemic lupus erythematous

Smoking tobacco

Rheumatoid arthritis

1st degree relative with low-trauma fracture

Steroid use

Personal history of low-trauma fracture

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