The requirements and development of neutron beams for neutron capture therapy of brain cancer

One of the two overriding conditions for successfulBNCT is that there must be a sufficientnumber of thermal neutrons delivered to each ofthe boronated cells in the tumour bed (targetvolume). Despite the poor experience with BNCT inthe USA some 40 years ago, the continuedapparent success of BNCT in Japan since 1968,lead indirectly to the re-start of clinical trialson BNCT in 1994 at both Brookhaven andMIT. Similar trials will start soon at Pettenin Europe. At other centres worldwide, many neutronbeam designs are being proposed with either thermalor epithermal neutrons, emanating predominately from nuclear researchreactors. It is apparent that whilst the successof BNCT depends on a suitable neutron beam,there is a diversity in available designs, aswell as each proposed type of neutron source,with consequently different characteristics of the emergent neutronbeam. The paper presents the historical development ofneutron beams used for BNCT, addresses the requirementson the types of beams, describes some ofthe existing designs and other proposals elsewhere andlastly, considers the broader requirements in designing NCTfacilities. The focus of the paper is ontreatment of brain cancer, neutron beam requirements forother types of cancer may vary.