The Technique Of Neutron Source For Sulfur Neutron Capture Therapy

In 1936,G.Locher proposed to use neutron capture reaction in cancer treatment,so called as Boron Neutron Capture Therapy(BNCT).In that it uses high propensity of non-radioactive nuclide Boron-10 to capture thermal neutrons and results into the prompt nuclear reaction 10B(n,?)7Li.The products of this reaction have high linear energy transfer(LET),and the path lengths of these particles are in range of 4–10 ?m,so that their energy deposition is limited to the diameter of a single cell.In 1950,Brookhaven et al.built a thermal neutron source based on nuclear reactors,which was used for boron neutron capture therapy,and carried out the first clinical trial.Compared with the traditional radiotherapy treatment scheme,BNCT can selectively kill tumor cells without destroying the structure and function of normal tissue,which means that BNCT is an ideal radiotherapy scheme.Sulfur-33 has a resonance capture cross sections and releases 3.1 MeV alpha particles to effectively kill tumor cells in 13.5 keV neutrons,without secondary ?-rays produced.The sulfur abundance in human body is three orders of magnitude higher than boron abundance.The tumor tissues,compared with normal tissues,have a better selective absorption of sulfur carrier.In recent years,nuclear medicine researchers have proposed an emerging neutron capture therapy topic— Sulfur Neutron Capture Therapy(SNCT).SNCT can treat deep tumors with intermediate neutrons.SNCT,like BNCT,is a new and effective method for tumor therapy;it also can combine with BNCT to improve the effect of neutron capture therapy.There are several key obstacles to SNCT application.Firstly,how to build a suitable neutron source which can meet the treatment requirements of tumor and normal tissue dose,to achieve safe irradiation.Secondly,whether the cross section datum of 33S(n,?)30Si resonance reaction are reliable.At present,there are large differences in the available resonance cross section datum,which need to be verified by experimental means.With the excitation function characteristic of 33S(n,?)30Si resonance reaction in keV range,this paper proposes an accelerator-based neutron source in keV energy range with 7Li(p,n)7Be reaction.According to the "Target" simulation results,the most suitable experimental conditions of SNCT neutron source are determined,i.e.,the incident proton energy is close to the near threshold value,and the thick metal lithium target is used,which can contribute to enlarge the neutron yields in 0° incident direction.At same time,a neutron source based on 7Li(p,n)7Be reaction was established in tandem accelerator,and the time of flight method was used to measure the neutron spectrum from 7Li(p,n)7Be near threshold reaction to get neutrons in keV range.In order to provide a reference for actual clinical application,the neutron yields in resonance energy range,the Geant4 code was used to calculate the moderation performance of different moderating materials to determine a suitable neutron moderation scheme for the improvement of resonance neutron yields.According to the needs of neutron source radiation protection,a detailed analysis of biological dose of SNCT treatment has been finished,and a set of neutron source shield collimation system was established to shield the hall background irradiation dose,filter the ?-ray background from neutron beam,and improve the neutron beams collimation,to achieve safe irradiation.With the available datum of 33S(n,?)30Si cross section,an integral test scheme used for 33 S resonance reaction was designed to clarify the disagreement of experimental datum,and provide accurate and reliable datum for SNCT.