AN ANALYSIS OF MANDIBULAR BONE COMPLICATIONS IN RADIOTHERAPY FOR T1 AND T2 CARCINOMA OF THE ORAL TONGUE

Purpose: To examine the incidence of mandibular bone complication in p atients who underwent radiotherapy for T1 and T2 carcinomas of the ora l tongue and to analyze the factors contributing to its occurrence. Me thods and Materials: The clinical records of 148 patients with T1 and T2 carcinoma of the oral tongue treated with radiotherapy alone betwee n 1978 and 1989 were examined retrospectively, Interstitial brachyther apy, used as the major treatment modality, was performed using cobalt needles, radium needles, or iridium hairpins, The prescribed dose at t he plane 5 mm from the plane of the radioactive sources was 65-70 Gy i n interstitial brachytherapy alone, and 50-60 Gy in the combined treat ment with external irradiation, An external irradiation dose of 30 Gy was usually used. Results: Eleven of the patients showed radiation-ind uced mandibular bone complication. Two (1 T1, 1 T2) had been treated w ith interstitial brachytherapy alone, and nine (2 T1, 7 T2) with the c ombination of external irradiation and interstitial brachytherapy. The incidence of radiation complication of bone was significantly higher in the patients with T2 tumors (p = 0.04) and in those who received th e combined treatment (p < 0.01), Multivariate analysis revealed that t he total dose (p = 0.04) and dose rate of interstitial brachytherapy ( p = 0.03) were significant factors contributing to radiation bone comp lication, A significant difference in the incidence of bone complicati on was also seen between patients who received a total dose of 90 Gy o r more and those who received less than 90 Gy (p < 0.01), as well as b etween patients who were treated with 0.55 Gy/h or higher and those wh o were treated with less than 0.55 Gy/h (p = 0.03). Conclusion: A sign ificant increase in the incidence of bone complication was found at th e total dose of 90 Gy or more and at the dose rate of 0.55 Gy/h or hig her, In combined treatment with external irradiation and interstitial brachytherapy, the interstitial brachytherapy dose of 60 Gy appears to be the threshold at which mandibular bone complication is induced whe n the external irradiation dose is 30 Gy.