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Development and calculation of an energy dependent normal brain tissue neutron RBE for evaluating neutron fields for
J E Woollard1, T E Blue, N Gupta
1Nuclear Engineering Program, The Ohio State University, Columbus 43210, USA. jeff@bullmoose.eng.ohiostate.edu
Health Physics
|June 5, 2001
Summary
Developing accurate Relative Biological Effectiveness (RBE) models for Boron Neutron Capture Therapy (BNCT) is crucial for treating brain tumors. This study presents new RBE(En) expressions and validates their use in neutron field design for BNCT applications.
Area of Science:
- Medical Physics
- Radiation Oncology
- Nuclear Engineering
Background:
- Boron Neutron Capture Therapy (BNCT) is a binary treatment modality for malignant brain tumors.
- The energy dependence of Relative Biological Effectiveness (RBE) for epithermal neutrons, RBE(En), is critical for designing effective neutron fields in BNCT.
- Accurate RBE values are essential for dose calculations and treatment planning in BNCT.
Purpose of the Study:
- To develop an expression for the energy-dependent normal-tissue RBE, RBE(En), for epithermal neutrons.
- To calculate an estimate for RBE(En) for adult brain tissue.
- To develop separate RBE expressions for neutron interactions via the 14N(n,p)14C and 1H(n,n')1H reactions and evaluate their absorbed-dose-averaged values.
Main Methods:
- Development of an energy-dependent RBE expression for normal tissues.
- Calculation of RBE(En) for adult brain tissue.
- Derivation of RBE expressions for specific neutron interaction pathways (14N(n,p)14C and 1H(n,n')1H).
- Calculation of absorbed-dose-averaged RBE values using neutron flux spectra from the Brookhaven Medical Research Reactor (BMRR) and an Accelerator-Based Neutron Source (ABNS).
Main Results:
- The developed RBE(En) expression provides a reasonable estimate for adult brain tissue.
- Absorbed-dose-averaged RBE values for nitrogen (3.4) and hydrogen (3.2) interactions were calculated for the BMRR epithermal neutron beam, showing close agreement.
- RBE values for nitrogen, hydrogen, and brain tissue remained relatively constant with depth for the ABNS neutron source.
Conclusions:
- The close agreement between RBE(N) and RBE(H) supports the use of equal values for these parameters in BNCT research at Brookhaven National Laboratory.
- The constancy of RBE values with depth for the ABNS supports the use of constant RBE values in treatment planning, as practiced at BNL.
- The developed RBE(En) expressions contribute to improved neutron field design and dose calculations in BNCT for malignant brain tumors.