Monte Carlo Simulation of the UW Cyclotron
Robert D. Stewart, Ph.D.; Associate Professor of Medical Physics
School of Medicine, Department of Radiation Oncology, 1959 NE Pacific Street, Seattle, WA 98195

Fast Neutron Dosimetry, Microdosimetry and Relative Biological Effectiveness (RBE)

About

In the University of Washington Medical Center (UWMC) cyclotron, energetic (50.5 MeV) protons collide with a beryllium target to produce an intense beam of fast neutrons (Moffitt et al. 2016).  The beam of fast neutrons is collimated and then shaped to the (beams eye view) tumor contours using a multi-leaf collimator (MLC) (Moffitt et al. 2016).  For the endpoint of DNA double strand break (DSB) induction, CNTS neutrons have a relative biological effectiveness of about 2.8 + 0.1 (Stewart et al. 2015).  For salivary gland tumors, fast neutron treatments can achieve a 5-year local control rate of 75% compared to 32% for x-rays (Huber et al. 2001).  At the UWMC, Douglas et al. (1999) achieved a 9-year local control rate of 78% for lesions less than or equal to 4 cm.  For salivary gland tumors with skull base invasion, local control can be increased from 39% to 82% through the use of a stereotatic (photon) boost to the skull base (Douglas et al. 2008).

Although fast neutrons have been used to successfully treat salivary gland and selected other tumors for over 30 years (Laramore 2009 and references therein), the physical and biological mechanisms underpinning this form of cancer treatment are not fully understood.  To improve the clinical care of patients receiving fast neutron therapy, we are using advanced Monte Carlo simulation techniques to improve the accuracy of neutron dose estimates in patients.  We are also developing a multiscale system of biological models (Carlson et al. 2008, Stewart et al. 2011, Frese et al. 2012) to gain insight into the mechanisms that make fast neutrons so uniquely effective for the treatment of some cancers.  Through more accurate patient dosimetry and an improved understanding of biological mechanisms, we will be able to more fully individualize and exploit fast neutrons in the treatment of cancer.

1. Carlson DJ, Stewart RD, Semenenko VA, Sandison GA. Combined use of Monte Carlo DNA damage simulations and deterministic repair models to examine putative mechanisms of cell killing. Radiat Res. 169(4), 447-459 (2008).
2. Douglas JG, Lee S, Laramore GE, Austin-Seymour M, Koh W, Griffin TW. Neutron radiotherapy for the treatment of locally advanced major salivary gland tumors. Head Neck. 21(3), 255-263 (1999).
3. Douglas JG, Goodkin R, Laramore GE. Gamma knife stereotactic radiosurgery for salivary gland neoplasms with base of skull invasion following neutron radiotherapy. Head Neck. 30(4), 492-296 (2008).
4. Frese MC, Yu VK, Stewart RD, Carlson DJ. A mechanism-based approach to predict the relative biological effectiveness of protons and carbon ions in radiation therapy.  Int J Radiat Oncol Biol Phys. 83(1), 442-450 (2012).
5. Huber PE, Debus J, Latz D, Zierhut D, Bischof M, Wannenmacher M, Engenhart-Cabillic R. Radiotherapy for advanced adenoid cystic carcinoma: neutrons, photons or mixed beam? Radiother Oncol. 59(2), 161-167 (2001).
6. Laramore GE. Role of particle radiotherapy in the management of head and neck cancer. Curr Opin Oncol. 21(3), 224-231 (2009).
7. Stewart RD, Yu VK, Georgakilas AG, Koumenis C, Park JH, Carlson DJ. Effects of radiation quality and oxygen on clustered DNA lesions and cell death. Radiat Res. 176(5), 587-602 (2011)

8. G.B. Moffitt, R.D. Stewart, G.A. Sandison, J.T. Goorley, D.C. Argento, T. Jevremovic, MCNP6 model of the University of Washington clinical neutron therapy system (CNTS).  Phys. Med. Biol. 61 937-957 (2016).

9. R.D. Stewart, S.W. Streitmatter, D.C. Argento, C. Kirkby, J.T. Goorley, G. Moffitt, T. Jevremovic, George A. Sandison, Rapid MCNP Simulation of DNA Double Strand Break (DSB) Relative Biological Effectiveness (RBE) for Photons, Neutrons, and Light Ions.  Phys. Med. Biol. 60. 8249-8274 (2015).

Last updated: October 17, 2016
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