MCNP6 model of the University of Washington clinical neutron therapy system (CNTS)

Abstract

A MCNP6 dosimetry model is presented for the Clinical Neutron Therapy System (CNTS) at the University of Washington. In the CNTS, fast neutrons are generated by a 50.5 MeV proton beam incident on a 10.5 mm thick Be target. The production, scattering and absorption of neutrons, photons, and other particles are explicitly tracked throughout the key components of the CNTS, including the target, primary collimator, flattening filter, monitor unit ionization chamber, and multi-leaf collimator. Simulations of the open field tissue maximum ratio (TMR), percentage depth dose profiles, and lateral dose profiles in a 40 cm × 40 cm × 40 cm water phantom are in good agreement with ionization chamber measurements. For a nominal 10 × 10 field, the measured and calculated TMR values for depths of 1.5 cm, 5 cm, 10 cm, and 20 cm (compared to the dose at 1.7 cm) are within 0.22%, 2.23%, 4.30%, and 6.27%, respectively. For the three field sizes studied, 2.8 cm × 2.8 cm, 10.4 cm × 10.3 cm, and 28.8 cm × 28.8 cm, a gamma test comparing the measured and simulated percent depth dose curves have pass rates of 96.4%, 100.0%, and 78.6% (depth from 1.5 to 15 cm), respectively, using a 3% or 3 mm agreement criterion. At a representative depth of 10 cm, simulated lateral dose profiles have in-field (⩾ 10% of central axis dose) pass rates of 89.7% (2.8 cm × 2.8 cm), 89.6% (10.4 cm × 10.3 cm), and 100.0% (28.8 cm × 28.8 cm) using a 3% and 3 mm criterion. The MCNP6 model of the CNTS meets the minimum requirements for use as a quality assurance tool for treatment planning and provides useful insights and information to aid in the advancement of fast neutron therapy.

Induction of DNA Damage by Light Ions Relative to 60Co γ-rays

“…A peak RBE DSB value of 2.6 to 3.4 for high-LET carbon ions, as illustrated in Figure 3, is generally consistent with the RBE for fast neutron [74] and carbon ion [71] therapy clinical end points. Detailed Monte Carlo modeling of the University of Washington's clinical neutron therapy system [75,76], which is based on 50.5 MeV protons incident on a beryllium target, gives, for example, an RBE DSB of 2.8 6 0.1 (Stewart et al [3]).…”

Mechanistic Modeling of the Relative Biological Effectiveness of Boron Neutron Capture Therapy

“… A new CN source derived from the NM by removing the uranium sphere from the NM source. The UW CNTS [ 17 , 18 , 19 , 44 , 45 , 46 ], which uses 50.5 MeV protons incident on a Be target to produce a fast neutron energy spectrum. …”

“…In the UW CNTS, fast neutrons are produced by 50.5 MeV protons incident on a 10.5 mm thick beryllium target, primarily through ( p , n ) and ( p , n + p ) reaction, but a small portion are created through ( p , 2 n ), ( p , 3 n ), and ( p , n + α) reactions [ 19 ]. The incident proton beam was modeled in MCNP6 as a monoenergetic, monodirectional disk source of 0.5 cm radius, uniformly sampled.…”

“…The potential efficacy of BNCT using well-collimated, higher-energy neutron beams [ 15 , 16 ] is at an early stage of development, in part because very few facilities have the ability to deliver neutron beams shaped to the beams-eye view of an irregularly shaped tumor target. The University of Washington (UW) Clinical Neutron Therapy System (CNTS) is the only remaining operational facility in the U.S. with the ability to deliver 3D conformal fast neutron beams for the treatment of cancer [ 17 , 18 , 19 ].…”

“…Published studies of the measured cell surviving fraction for neutrons alone and in combination with boron are in good agreement with predictions from this system of Monte Carlo models. A MCNP (Monte Carlo N-Particle) model [ 19 ] of the University of Washington Clinical Neutron Therapy System (UW CNTS) and a few other neutron source models are used to explore the potential effectiveness of BNCT using BPA (boronophenylalanine) and a monoclonal antibody (mAb) that targets the HER-2 receptor. The impact of the microdistribution of 10 B within and near representative cells on the relative biological effectiveness (RBE) and compound biological effectiveness (CBE) is examined.…”