A comparison of clinical and laboratory data on neutron therapy for locally advanced tumors.

Experimental results suggest advantages for neutrons where cells are hypoxic, in tumors which are slowly growing and also in a relative sparing of bone damage. The neutrons available at Hammersmith were of 7.5 MeV energy and produced a poorly penetrating beam, unsuitable for treating tumors in the pelvis and abdomen. Patients with locally advanced tumors in superficial sites were therefore selected to assess the effects of neutrons on normal and malignant tissues. One hundred and eight-nine patients had between them 191 locally advanced (T4 N0-3) tumors in the oral cavity, paranasal sinuses, salivary glands, and breast. Neutron therapy resulted in complete regression in 84% of which 13% subsequently recurred. Median survival for the whole group was 32 months. Twenty-eight other patients had advanced tumors of the head and neck which were recurrent after X ray therapy and other treatments; 82% of these completely regressed for more than 1 year. Complications appeared in 27% of patients not previously treated and in 46% who had already undergone X ray therapy. Seventy-four per cent of complications started in the skin. With neutrons of this energy there is minimal sparing of the skin and uneven distribution of dose resulting in "hot" spots. These affected skin, subcutis, and muscle. The high rates of control in these large tumors, the low incidence of bone necrosis, and the repair of some bones eroded by tumor correlate well with the experimental data. There was rapid regression of the tumor and close correlation between early and late effects on skin and subcutis. These two observations may relate to the fractionation, total dose, and overall time of treatment of 1560 cGy neutron dose given in 12 fractions over 28 days.