Late normal tissue sequelae from radiation therapy for XXXX : patterns of fractionation study of radiobiology.

@entity1 @entity353 @entity39 @entity1066 @entity5932 @entity189 @entity121 @entity3137
PURPOSE: To evaluate the influence of dose fractionation and other factors on the development of late complications in mandibular bone, muscle, and mucosa of the oral cavity after external beam radiation therapy for @entity189 . METHODS AND MATERIALS: A retrospective analysis was made of the results in 676 @entity1 treated with a spectrum of fractionation regimens in nine centers during the years 1976-1985. Only severe (Grades 3-4) late complications were analyzed. RESULTS: With more than 5 years follow-up, it was found that total dose was a factor for all three types of complications, but that in other respects, the radiobiology of late-(> 3 months) developing mucosal @entity1066 was different from that for mandibular @entity39 and @entity121 . Dose per fraction was a significant factor for bone and muscle (estimated alpha/beta values of 0.85 Gy and 3.1 Gy, respectively). By contrast, mucosa showed no influence on response from change in fraction size over the range of approximately 1.0-3.5 Gy. Complications in bone and muscle were not related to overall treatment duration, whereas there was a significant inverse relationship for @entity5932 . The rate of development of complications was fastest in mucosa and slowest in bone. The appearance of complications by 4 years after treatment was about 80% of those developing by 8 years in the mucosa, 66% in muscle, and about 50% in bone. The high alpha/beta ratio, inverse relationship with overall treatment duration, and @entity3137 suggests that they may develop as a consequence of earlier @entity3137 . As anticipated, adequate retrospective analysis of acute complications could not be made even when objective criteria such as @entity353 , unplanned delays in completing treatment, or hospitalization during treatment were the measures. Field size was a significant factor for mandible complications, but not for muscle or mucosa. CONCLUSION: The radiobiological characteristics of bone and muscle were those characteristic of other late-responding tissues, whereas late sequelae in mucosa had radiobiological parameters similar to those for acute responses. Field size was a significant factor for bone complications but not for others.
