Differential attenuation of clavicle growth after asymmetric mantle radiotherapy

Purpose To determine the effects of 15 Gy on bone growth as a function of time and age by comparing clavicle length before and after asymmetric mantle irradiation in pediatric patients. Methods and materials We measured the lengths of both clavicles from radiographs made before and after radiotherapy (median follow-up, 39.6 months), in 15 children (median age, 13.3 years) with early-stage Hodgkin's disease treated with combined modality therapy. The intercepts and slopes of regression lines for individual patients were used to form an estimating regression curve for the population. Results The irradiated volume, patient age, and time elapsed after treatment influenced the measured growth. Fully irradiated clavicles grew 1.3 ± 0.3 cm, significantly less (0.5 cm; p = 0.007) than did the partially irradiated clavicles. The difference between partially and fully irradiated clavicle lengths was statistically significant, regardless of age. Also, the growth rate of partially and fully irradiated clavicles was significantly different between younger (mean age, 9.9 years) and older (mean age, 16.4 years) patients (p = 0.036). Conclusion Clavicle growth is vulnerable to radiation doses as low as 15 Gy, and patient age at the time of irradiation influences the growth rate.