The fate of patients with either incomplete resection, metastatic disease in the regional lymph nodes, or both is poor. It has also been well demonstrated that radiation therapy is capable of sterilizing residual cancer in either the tumor bed region, the regional lymph nodes, or in both, when an adequate radiation dose is administered in thoracic and other malignant tumors.10 In squamous cell carcinoma of the lung, postoperative radiotherapy using a moderate dose of radiation (45 to 54 Gy in 25 to 30 fractions over a period of 5 to 6 weeks) showed a significant improvement in locoregional tumor control.11 If it is assumed that the
radiation response of primary squamous cell carcinoma of the trachea and carina are similar to that of bronchogenic carcinoma, then postoperative radiotherapy would be a valuable adjuvant treatment for patients with either incomplete resection, metastatic disease in the regional lymph nodes, or both.
Even though there are not enough reports on the role of postoperative radiotherapy in adenoid cystic carcinoma of the trachea and carina,12,13 an analogy, which can be drawn from the clinical experience in adenoid cystic carcinoma of the minor salivary glands in the head and neck region, may be a useful guide. Douglas and colleagues reported results of neutron radiotherapy for patients with gross residual adenoid cystic carcinoma of minor salivary glands after attempted surgical resection.14 The median dose was 19.2 neutron Gy in 1.2 neutron Gy doses, given 4 times a week. The median duration of follow-up was 32 months. Sites of the primary disease and the number of patients treated per disease site were as follows: paranasal sinus, 31; oral cavity, 20; oropharynx, 12; nasopharynx, 11; trachea, 6; and other sites in the head and neck, 4. The 5-year actuarial locoregional tumor control rate for all patients treated with curative intent (n = 72) was 47%. The 5-year actuarial overall survival and cause-specific survival were 59% and 64%, respectively. Patients with adenoid cystic carcinoma of the oral cavity and oropharynx were able to receive the intended dose of neutron radiation (19.2 neutron Gy), whereas those with a primary lesion in the nasopharynx and paranasal sinus with skull base involvement were treated with a lower dose of neutron radiation (12 neutron Gy) because of the risk of normal tissue injury at the skull base and brain stem. Five-year locoregional tumor control was 59% for patients treated with a high neutron dose for the primary oral cavity and oropharyngeal lesions, whereas it was 18% for those treated with a low neutron dose for the nasopharynx and paranasal sinus lesions involving the skull base and brain stem.
Both photons and neutrons have been used for postoperative radiotherapy for residual tracheal adenoid cystic carcinoma. Douglas and colleagues treated 5 patients with residual tracheal adenoid cystic carcinoma postoperatively with neutron radiation.14 Five-year locoregional control, overall survival, and cause-specific survival were 40%, 67%, and 67% respectively. Ogino and colleagues treated 7 patients with adenoid cystic carcinoma of the trachea for incomplete resection margins with photon radiation.12 Local tumor control was obtained in 3 of 4 patients when the radiation dose administered was 60 Gy or higher, and in 1 of 3 patients when the administered radiation dose was less than 60 Gy.
Therefore, it seems likely that a radiation dose of 60 Gy in 2 Gy dose fractions, 5 fractions per week, over a period of 6 weeks of photon radiation, or a biologically equivalent dose of neutron radiation, is necessary to convert a surgical resection from incomplete to complete, by sterilizing residual microscopic carcinoma in the tumor bed and regional lymph nodes in both squamous cell carcinoma and adenoid cystic carcinoma. Such postoperative radiotherapy is likely to result in an improvement in survival. For gross residual carcinoma, the radiation dose needs to be increased to 68 to 70 Gy in 2 Gy dose fractions, 5 fractions per week, over a period of 6.8 to 7 weeks.
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