Peter Johnstone was raised in Gresham, Oregon. He graduated from the United States Naval Academy in 1979, completing a Master of Arts degree in Communication from Oklahoma University in 1985 and an M.D. degree from the Uniformed Services University of the Health Sciences in 1989. He completed Residency in Radiation Oncology subsequently at the National Cancer Institute. In December, 2007, Dr. Johnstone was named Chair and William A. Mitchell Professor of Radiation Oncology at Indiana University (IU). He was named President and Chief Executive Officer of the IU proton center in August, 2008, and director of IU cyclotron operations in January, 2010. Dr. Johnstone was selected to the ACR Board of Chancellors in 2011, and served as President of the American Radium Society in 2010, and President of the Society for Integrative Oncology in 2007.