BORON NEUTRON-CAPTURE THERAPY - A MECHANISM FOR ACHIEVING A CONCOMITANT TUMOR BOOST IN FAST-NEUTRON RADIOTHERAPY

Purpose: For many years neutron radiation has been used to treat malig nant disease both as fast neutron radiotherapy and as thermal neutron induced boron neutron capture therapy (BNCT). To date, these two appro aches have been used independently of one another due to the large dif ference in neutron energies each employs. In this paper we discuss the potential application of BNCT to enhance the therapeutic effectivenes s of a fast neutron radiotherapy beam. Methods and Materials: Measurem ents are presented for the thermal neutron component that is spontaneo usly developed as the University of Washington fast neutron radiothera py beam penetrates a water phantom. The biological effect of this ther malized component on cells ''tagged'' with boron-10 (B-10) is modeled mathematically and the expected change in cell survival calculated. Th e model is then extended to estimate the effect this enhanced cell kil ling would have for increased tumor control. Results: The basic predic tions of the model on changes in cell survival are verified with in vi tro measurements using the V-79 cell line. An additional factor of 10- 100 in tumor cell killing appears achievable with currently available B-10 carriers using our present neutron beam. A Poisson model is then used to estimate the change in tumor control this enhanced cell killin g would produce in various clinical situations and the effect is suffi ciently large so as to be clinically relevant. It is also demonstrated that the magnitude of the thermalized component can be increased by a factor of 2-3 with relatively simple changes in the beam generating c onditions. Conclusion: BNCT may provide a means of enhancing the thera peutic effectiveness of fast neutron radiothearapy in a wide variety o f clinical situations and is an area of research that should be aggres sively pursued.