Interstitial brachytherapy for stage I and II squamous cell carcinoma of the oral tongue: factors influencing local control and soft tissue complications.
OBJECTIVE
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 brachytherapy (BRT) alone (127 patients), or by a combination using external beam irradiation (EBI) (80 patients) between 1980 and 1993.


METHODS
The patient distribution was 93 T1, 72 T2a, and 42 T2b. The prescribed BRT dose at the plane 5 mm from the plane of the radioactive sources was 65-70 Gy in BRT alone, and 50-60 Gy in the combined treatment using EBI. Generally, an EBI dose of 30 Gy was used. No prophylactic neck 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 appearance and those located in the posterior half of the mobile tongue had a significantly lower local control rate than those of other macroscopic appearances (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 alone 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 local control; however, the incidence of local recurrence was lowest in a BRT dose 65-70 Gy. In the combined treatment, a total dose > 85 Gy (p = 0.01), BRT dose > 55 Gy (p = 0.04), and a dose rate < 0.55 Gy/h (p = 0.03) were significantly related to better local control. The incidence of more severe STC 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 was significantly related to more STC in BRT alone (p = 0.03), and that a dose rate > = 0.55 Gy/h (p < 0.03) and a BRT dose > 70 Gy ( < 0.05) and a total 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. Thirty-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.


CONCLUSIONS
To acheive better local control and fewer STC, we recommend the following relationships between dose and dose rate. In BRT alone, dose rate should be maintained at < 0.6 Gy/h with a preferable BRT dose 65-70 Gy. In 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 Gy/h, respectively. We also recommend longer follow-up periods; more than 5 years might be necessary for late local recurrences and for secondary cancers.
Fujita
M
M
Department of Oral and Maxillofacial Radiology, Hiroshima University School of Dentistry, Japan. mfujita@ipc.hiroshima-u.ac.jp
Hirokawa
Y
Y
Kashiwado
K
K
Akagi
Y
Y
Kashimoto
K
K
Kiriu
H
H
Matsuura
K
K
Ito
K
K
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D002294:Carcinoma, Squamous Cell / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*; D002423:Cause of Death; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000453:epidemiology; D009367:Neoplasm Staging; D011832:Radiation Injuries / Q000209:etiology; D011879:Radiotherapy Dosage; D017695:Soft Tissue Injuries / Q000209:etiology; D014062:Tongue Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy*