The CTRx, a therapy machine and CT scanner

The idea for X-ray phototherapy (XPT) - the use of contrast media to enhance the X-ray dose absorbed by tumors - and the development of the CTRx to deliver it started with a visit to the author by Forrest Adams, a pediatric cardiologist, some two decades ago. He was concerned because of the very long X-ray exposures, frequently exceeding 30 minutes and sometimes over 60 minutes, that his patients, infants and young children, were receiving during angiography. Two recent developments make the prospects for XPT, delivered by a CTRx, bright. The first is the current development of table top monoenergetic X-ray sources based on the Compton scattering of laser photons from relativistic electron beams. This will allow matching the X-ray energy to the peak of the DEF vs photon energy curves. The other is the development of CM that are targeted to tumors