Woodruff School of Mechanical Engineering

NRE/MP Seminar

Nuclear & Radiological Engineering and Medical Physics Programs


Intensity Modulated Neutron Therapy


Dr. Robert Stewart


University of Washington


Thursday, October 14, 2021 at 11:00:00 AM   Add to Calendar


Boggs Building, Room https://bluejeans.com/787057709/8248




Purpose High linear energy transfer LET neutrons have been used to treat over 3,300 patients at the UW because of their ability to overcome multiple mechanisms of resistance to low LET radiations. Technical and clinical challenges of implementing IMNT are presented along with an analysis of the potential therapeutic benefits. Methods A commercial treatment planning system TPS has been modified to incorporate neutron scattering kernels and accommodate the unique characteristics of the Clinical Neutron Therapy System CNTS. A Monte Carlo model of the CNTS has been developed to independently confirm TPS doses. A portal imaging system based on 11C positron emission tomography has also been developed for physics quality assurance QA. Results Comparisons of measurements, TPS and Monte Carlo doses are in excellent agreement 3 percent 3mm analysis for a wide range of field sizes, both open and wedged. A comparative analysis of IMNT plans for seven head and neck patients shows an average 56 percent decrease in organ at risk dose compared to 3D conformal neutron therapy 3DCNT. The maximum dose decreased by 20 percent and 21 percent for the spinal cord and temporal lobe, respectively. The mean larynx D50 percent decreased by 80 percent. The overall number of monitor units for wedged and IMNT treatments is similar. Conclusions With IMNT, comparative planning studies demonstrate significant reductions in OAR dose are possible with similar target coverage. Clinical trials to compare 3DCNT to IMNT are in development. Such trials will inform ongoing work to evaluate the use of other types of high LET radiations for patient care, including carbon ions.


Dr. Stewart is an Associate Professor of Radiation Oncology and a Medical Physicist in the University of Washington UW Department of Radiation Oncology 2010 – present. He graduated from Kansas State University in 1997 with a Ph.D. in Mechanical and Nuclear Engineering. He was a Senior Research Scientist at Pacific Northwest National Laboratory from 1990-1993 and from 1997-2002. He transitioned to Purdue University in 2002 as an Assistant Professor. He served as the Assistant Head of the School of Health Sciences 2008 2010 and Director of the Health Physics and Medical Physics programs at Purdue University 2006 2010. He served as a Physics Councilor for the Radiation Research Society 2005 2008 and as a member of AAPM Task Group 256 on proton relative biological effectiveness RBE. He is currently the UW lead for clinical radiation biology, the physics lead for the UW neutron therapy program and an associate editor for the British J. of Radiology. He has published over 70 journal articles and book chapters and is well known for his efforts to advance multiscale biological modeling of radiation effects, especially as it relates to particle RBE.