Applicability of the 9Be(d,n)10B reaction to AB-BNCT skin and deep tumor treatment

M.E. CAPOULAT; D.M. MINSKY; A.J. KREINER

Buenos Aires

Congreso; 14th International Congress on Neutron Capture Therapy; 2010

International Society for NeutronCapture Therapy

Presentación Oral (M.E. Capoulat)Introduction: In the range of low bombarding energies (1.0 to 1.5 MeV) the 9Be(d,n)10B reaction produces neutron spectra which can easily be moderated depending on the choice of the target thickness and the deuteron bombardment energy. In this work, a simulation study to determine the capability of this reaction to deliver enough dose to efficiently control both skin and deep seated tumors has been performed by means of MCNP calculations using eight optimized 9Be targets. Materials and Methods: For the target optimization, a pool of computational neutron sources with target thicknesses from about 0.9 to 8 ?m and bombarding energies from 1.0 to 1.5 MeV were built taking into account energy-angle distributions available in the literature. The optimal thickness for each bombarding energy was determined so that the above-to-below 1 MeV neutron energy rate was minimized. A Snyder’s head phantom was considered for skin and brain tumors and all tissue compositions were taken from the ICRU-63 report. In the case of skin tumors the moderation was simply accomplished by using a D2O volume delimited by reflecting lead walls. A bismuth layer of about 3 cm was added on the beam port in order to reduce dose due to gamma emissions from excited states of the residual nucleus 10B. In the case of brain tumors, we considered an array of Al, polytetrafluoroethylene (PTFE) and LiF layers as moderator. A 1 cm acrylic layer was added for further reduction of fast neutron dose. We also used lead to surround the beam shaping assembly as a reflector for fast neutrons.  Treatment times were calculated for each computational source as the required time to deliver enough dose to reach tumor control probabilities (TCP) above 98% assuming a 30 mA deuteron beam.  Results and Discussions: For bombarding energies from 1.25 to 1,45 MeV, tumor control probabilities above 98% were reached after treatment times from 20 to 60 minutes for skin tumor treatment. In this case, the maximum total dose delivered to healthy skin and brain were lower than 13 and 9 RBEGy after a whole treatment respectively. For deep seated brain tumors, treatment times required to reach a TCP of 98% are longer than 50 min and the maximum total dose delivered to healthy tissue, in particular to skin, resulted too high for all the neutron sources. The maximum total dose delivered to healthy tissue for a 5cm deep seated tumor was about 20 and 11 RBEGy for skin and brain respectively. This dose contribution primarily belongs to fast neutron scattering on 1H present in tissue and can be reduced by adding hydrogenated materials to the moderating volume. These materials will also reduce thermal and epithermal contributions, so that total neutron yield will also be decreased and therefore longer treatment times (or larger beam currents) will be required. Nevertheless, we do not discard the applicability of the 9Be(d,n)10B reaction to deep seated tumor treatments as we consider it likely that a more exhaustive optimization of the beam shaping assembly will improve the results. Finally, it must be emphasized that the lack of accurate and complete information about this reaction allows only an approximation to realistic models of neutron sources and hence we consider that a comparison against future experimental data is reccomended.