Scheduling of hypoxic-tumor therapy using neutron brachytherapy.

Fast-neutron-beam therapy and low-dose-rate fast-neutron intracavitary therapy of cervical carcinoma are effective in producing regression of advanced tumors. However, effectiveness is critically dependent on the schedule by which they are used in combination with fractionated external low-linear-energy-transfer (LET) therapy. Neutron-beam therapy is now alternated frequently with fractionated external radiotherapy (mixed beam). Intracavitary neutron therapy, scheduled before fractionated external-beam photon therapy, was maximally effective. These findings indicate that traditional concepts developed for the use of conventional low-LET therapy may need to be altered to use neutrons for therapy and to achieve improved local control of advanced cancers.