Professor Thomas Merchant is a pediatric radiation oncologist and Chair of the Department of Radiation Oncology at St. Jude Children’s Research Hospital in Memphis, Tennessee, USA. His practice spans 30 years. Dr. Merchant pioneered the use of radiotherapy for very young children with brain tumors. As past Chair of the Radiation Oncology Discipline Committee for the Children’s Oncology Group, he worked to implement conformal photon and proton therapy guidelines for children enrolled in cooperative group trials. Taking advantage of his training as a nuclear engineer and experience in medical imaging, Dr. Merchant designed and developed the world’s first proton therapy center dedicated solely to the treatment of children. The St. Jude proton therapy center is the busiest pediatric radiotherapy facility in North America.