Interstitial brachytherapy for stage I and II squamous cell carcinoma of the oral tongue: Factors influencing local control and soft tissue complications

Purpose: Our aim was to study the treatment parameters that influence local control and soft tissue complications (STC) in a series of 207 Stage I and II squamous cell carcinomas of the oral tongue treated by interstitial bra chytherapy (BRT) alone (127 patients), or by a combination using external b eam irradiation (EBI) (80 patients) between 1980 and 1993. Methods and Materials: The patient distribution was 93 T1, 72 T2a, and 42 T 2b. The prescribed BRT dose at the; plane 5 mm from the plane of the radioa ctive sources was 65-70 Gy in BRT alone, and 50-60 Gy in the combined treat ment using EBI. Generally, an EBI dose of 30 Gy was used. No prophylactic n eck treatment was performed. Results: The 5-year local recurrence-free rate for T1, T2a, and T2b was 92. 9%, 81.9%, and 71.8%, respectively (p < 0.05). The lesions of endophytic ap pearance and those located in the posterior half of the mobile tongue had a significantly lower local control rate than those of other macroscopic app earances (p = 0.02) and those in other localizations (p < 0.01). Most local recurrences (66.7%) occurred within 2 years after treatment. However, 8 of 14 recurrences of T1 and 6 of 15 recurrences among patients treated by BRT alone occurred after 5 years. Statistical analysis showed that, in BRT alo ne treatment, a dose rate < = 1.0 Gy/h was related to better local control (p = 0.04). There was no significant relationship between BRT dose and loca l control; however, the incidence of local recurrence was lowest in a BRT d ose 65-70 Gy. In the combined treatment, a total dose > 85 Gy (p = 0.01), B RT dose > 55 Gy (p = 0.04), and a dose rate < 0.55 Gy/h (p = 0.03) were sig nificantly related to better local control. The incidence of more severe ST C were 11.5% and was significantly higher in T2a (p 0.03) and T2b (p < 0.01 ) than in T1. Statistical analysis revealed that a dose rate > = 0.6 Gy/h w as significantly related to more STC in BRT alone (p = 0.03), and that a do se rate > = 0.55 Gy/h (p < 0.03) and a BRT dose > 70 Gy (p < 0.05) and a to tal dose > 100 Gy (p < 0.05) were significantly related to more STC in the combined treatment. Neck metastases occurred in 25% in T1N0, 27% in T2aN0, and 31% in T2bN0 (NS). Eighty-eight percent were found within 12 months. Th irty-three secondary cancers including 12 head and neck, 8 esophageal, and 3 gastric were found after treatment. The 5-year crude survival rate for T1 , T2a, and T2b was 83.4%, 66.0%, and 70.9%, respectively. Conclusion: To acheive better local control and fewer STC, we recommend the following relationships between dose and dose rate. In BRT alone, dose rat e should be maintained at < 0.6 Gy/h with a preferable BRT dose 65-70 Gy. I n the combined treatment, total dose, BRT dose and dose rate should be kept between > 85 Gy and < = 100Gy, between > 55 Gy and < = 70 Gy, and < 0.55 G y/h, respectively. We also recommend longer follow-up periods; more than 5 years might be necessary for late local recurrences and for Secondary cance rs. (C) 1999 Elsevier Science Inc.