Postoperative radiotherapy for oral cancers. Radiation fields and recurrence patterns according to tumor residuals

To improve tumor control of oral cancers by postoperative radiotherapy, the relation between radiation fields and recurrence patterns was studied according to postoperative tumor residuals. Between 1984 and 1998, 36 patients with squamous cell carcinoma of the oral cavity underwent postoperative radiotherapy. They consisted of 5 stage I-IIIs, 15 stage IVs, and 16 recurrences. There were 19 local residuals (7 microscopically and 12 macroscopically) and 8 nodal residuals (5 microscopically and 3 macroscopically). The mean dose of postoperative irradiation was 52 Gy in 25 fractions over 35 days. The overall 5-year survival rate and disease-free survival rate were 38% and 21%, respectively. Twenty patients had recurrences within 6 months and 4 patients had recurrences at the primary site around 4 years after irradiation. Recurrence rates were significantly associated with the tumor residuals and the number of positive nodes. The tumor control rates were 5/16 (31%) for local residuals alone, 2/5 for nodal residuals alone, and 0/3 for both local and nodal residuals. For 9 patients without nodal disease, radiation fields to the primary site developed 3 in-field recurrences and no out-of-field recurrence (control rate: 6/9). For 9 patients with pathologically positive nodes completely resected and without local residuals, the radiation fields to the neck only developed late recurrences at the primary site in 4 of 5 patients, while the radiation fields also including the primary site developed no recurrence at the primary site in 4 patients (control rate: 3/9). The recurrence patters were significantly different between them. For 10 patients with pathologically positive nodes completely resected and with local residuals, radiation fields mainly to local residuals developed 3 out-of-field recurrences of 4 nodal recurrences (control rate: 2/10). The out-of-field recurrence rates were not different statistically between parallel as opposed to lateral ports and hemi-lateralized fields. No out-of field recurrence occurred in patients with irradiation fields including lower neck nodes. Radiation fields according to postoperative residuals played a role for loco-regional control. For patients without nodal disease, the radiation field including only the primary site was recommended considering the patient's quality of life. For patients with nodal disease, large field adding the primary site and lower neck field would improve the postoperative irradiation results. However, the hemi-lateralized radiation fields instead of the parallel as opposed to lateral ports is possible for some patients. (author)