Radiotherapy

Pleomorphic adenomas are essentially benign tumours. However, the rate of local recurrence after local enucleation has led to the use of post-operative radiotherapy by some; there is no proof that this is beneficial. A lapse of 10 years or more is seen in about half of all those patients who relapse. Better treatment is the removal of the lump with an adequate wide margin of normal tissue.

When a mucoepidermoid or acinic cell tumour is removed, there is no place for radiotherapy unless there is concern about the margin of normal tissue.

In malignant salivary gland tumours, post-operative radiotherapy reduces the incidence of local recurrence. With clinically malignant tumours arising in the parotid gland, post-operative radiotherapy is indicated when:

♦ The tumour is high-grade

♦ The surgical margins are close

♦ Resection has been performed for recurrent disease

♦ There is invasion of extra-parotid tissue

♦ There is regional node involvement

♦ There is gross residual post-operative disease

Orthodox radiotherapy techniques use 6-10 MV photons, often with a wedged pair of fields, to give a dose of 55-65 Gy over 6-7 weeks. The tumour volume will include the courses of adjacent cranial nerves up to the skull base, to control any perineural spread (which is particularly common with adenoid cystic carcinoma). Dryness of the mouth is usual but recovers if the opposite salivary glands are avoided. Trismus is common following treatment.

Pre-operative radiotherapy may be advantageous in the management of large tumours, particularly those considered to be inoperable. The situation should be reviewed after 45-50 Gy, when tumour shrinkage may have already made surgery possible. Split-course postoperative radiotherapy is given as soon as possible after healing—a further 20-25 Gy in 2-3 weeks.

Electron therapy has potential advantages in the treatment of parotid tumours. More recently other forms of particulate irradiation have been used, in particular neutrons. In a multi-centre randomized study of patients with locally advanced parotid gland cancer, with neutrons a local control rate of 67% was obtained, whereas the rate for photons was 17%.

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