Results of external beam radiotherapy in differentiated thyroid carcinoma: a retrospective study from the Royal Marsden Hospital.

Between 1969 and 1991, 113 patients with differentiated thyroid carcinoma (follicular and papillary) received radical dose megavoltage external beam radiotherapy. There were 70 females and 43 males, mean age 53 years (range 11-84). Radiotherapy was delivered to both sides of the neck and superior mediastinum, using either megavoltage photons via anterior and posterior portals, delivering a 60 Gy mid-plane dose in 30 fractions and treating daily over 6 weeks (with spinal cord shielding from the posterior field after 40 Gy), or matched 20 MeV and 35 MeV electron beams (to the neck and superior mediastinum, respectively) delivering a 75 Gy applied dose in 30 daily fractions. All patients received suppressive thyroid hormone and 74 radioiodine. Local recurrence, mostly within field, occurred in 19% of 53 patients with probable and definite residual microscopic disease (both follicular and papillary histologies). For gross residual disease (both follicular and papillary) in 49 patients, complete regression was obtained in 37.5%, partial regression in 25% and no regression in 37.5%. Median follow-up from diagnosis was 49 months (range 3-335). Overall 5-year survival rates were 85% for residual microscopic disease but only 27% for gross disease. 61 patients have died. Nineteen deaths were due to unrelated causes, 15 to distant metastases, 15 to uncontrolled local disease and 12 died with both local and distant tumours.