Locally advanced breast cancer treated with neutron beams: long-term follow-up in 28 patients.

Between 1972 and 1978, 28 patients with locally advanced breast cancer were treated, 15 with neutron beams only and 13 with mixed neutron and photon beams. Half the patients had inflammatory cancer. For neutrons only, doses ranged between 13.35-25.34 nGy. In mixed-beam regimens, the prescribed total dose ranged between 62 and 76 Gy photon equivalent. Nine patients (32%) had a complete response without local recurrence for the duration of their survival ranging from 1 to 14+ years; 18 patients had a partial response (64%); and one patient had no change. Late toxicity was high: of 24 patients who received tangential breast irradiation, 5 (21%) had ulceration of the breast or chest wall, or both. In four patients, mastectomy and skin grafts were necessary for repair. In only one patient did the skin necrosis heal without corrective surgery. Twelve patients received axillary neutron irradiation, resulting in severe edema in four patients, and brachial plexopathy in six patients. Radiation-induced complications progressed steadily for the duration of the patients' survival after the neutron irradiation. The high complication rate encountered is attributed to high doses resulting from an under estimation of the relative biological effect of the neutron beam for late effects, and to the poor physical and geometrical characteristics of the neutron beam.