Head phantom irradiation modelling using the final FIR 1 epithermal neutron beam

Tiina Seppälä, Iiro Auterinen, Pekka Hiismäki, Sauli Savolainen

    Research output: Chapter in Book/Report/Conference proceedingConference abstract in proceedingsScientific

    Abstract

    In the Finnish BNCT (boron neutron capture therapy) project the final configuration of the FiR 1 beam for BNCT treatments was completed in September 1996. The beam collimator was installed to the front of the basic beam to have a safe and spacious treatment place for the patient. The neutron and gamma fields induced in the phantom were also changed, Results of radiation transport calculation for this collimation design using the DORT code are reported here. The collimator is a truncated cone, which converge toward to the beam output. The neutron flux is collected from the bismuth face, which is the output of the reactor epithermal neutron moderator system. The collimator is made of bismuth and lithiated polyethylene. The bismuth cone was added to the innerside of the lithiated polyethylene collimator to reflect the neutrons back to the neutron beam. When 6 cm lithiated polyethylene was replaced by bismuth cone in the innerside of collimator the maximum of thermalized neutron field grew 40 % in the human head phantom. The free epithermal neutron flux decrease 58 % from the bismuth face to the collimator output. The distance of these two points is 47 cm. The collimation of the beam also increase the degree of dose uniformity thoughout the patient head and the dose maximum is transferred 0.5 em deeper. The collimator was also needed to get enough place for patient treatment. When the collimator is used in BNCT treatments, patients can be rotated 118 degrees around the beam apeture in horizontal plane. Dose to other parts of patient body was also decreased. The walls near the treatment position were covered by lithiated polyethylene and lead layer to cut the neutron and gamma flux from the structure. The calculated model used was verified by the activation and the twin ionization chambers measurements. According to the calculation the FiR 1 epithermal beam can be used in this configuration for BNCT.
    Original languageEnglish
    Title of host publicationProceedings of the XXXI Annual Conference of the Finnish Physical Society
    Subtitle of host publicationAbstracts
    EditorsEero Rauhala, M.E. Sainio
    Place of PublicationHelsinki
    PublisherUniversity of Helsinki
    ISBN (Print)951-45-7639-X
    Publication statusPublished - 1997
    MoE publication typeNot Eligible
    EventXXXI Annual Conference of the Finnish Physical Society - Helsinki, Finland
    Duration: 13 Mar 199715 Mar 1997

    Publication series

    SeriesUniversity of Helsinki: Department of Physics. Report Series in Physics
    Volume262
    ISSN0355-5801

    Conference

    ConferenceXXXI Annual Conference of the Finnish Physical Society
    CountryFinland
    CityHelsinki
    Period13/03/9715/03/97

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