Hip stiffness following mixed conformal neutron and photon radiotherapy: A dose-volume relationship

Purpose: To determine the relationship between dose, volume, and the incidence of hip stiffness in patients who received conformal neutron irradiation for nrostate cancer. Methods and Materials: A series of dose-searching studies using neutron irradiation for prostate cancer were performed to determine the optimal dose, fraction size, field size, technique, and proportions of photon and neutron dose. Neutron doses ranged fro& 9 to 20 Gy and photon doses ranged frbmb to 38 Gy: Data were analyzed by using a hip stiffness grading scale. Results: Hip stiffness was recorded on follow-up examination in 30% of patients (40 out of 132) treated with fast neutrons or mixtures of fast neutron and photon radiation for prostate cancer. Hip stiEness was categorized as none (Grade 0,92 patients), mild (Grade 1,24 patients), moderate (Grade 2,10 patients), or severe (Grade 3,6 patients). The incidence of hip stiffness differed significantly by dose and volume in the five dose levels studied @ < 0.001). Conclusions: By using a mixture of conformal neutron and photon irradiation and limiting the total neutron dose to less than 13 Gy, hip stiffness toxicity could be reduced to acceptable levels. Radiotherapy side effects, Fast-neutron radiation