Breakthrough technology that moves radiation beyond 3 D conformal therapy, then past IMRT and IGRT to achieve ART. 

Once CT scans and computers were used to identify targets for radiation treatment in the 1990's, the beam could be conformed (or modified) to better hit the tumor and avoid normal structures in three dimensions (called 3D conformal therapy.) Often 5 or 6 separate beams were used.

 

Later in 1990's and early 2000's the beams could be further modified to  even more accurately hit the target using a technique called Intensity Modulated Radiation Therapy (IMRT ).  Then imaging devices were attached to the linear acceleratory to better ensure that that target was set up accurately every day using a technique called Image Guided Radiation Therapy (IGRT). Often as many as 7 or 9 beams were used to provide even more sophisticated targeting

Finally the ultimate machine was designed and built using technology similar to a CT scanner.  Just as a CT scan provides extremely precise and detailed information about normal and abnormal anatomy,  the TomoTherapy treatment device is able to deliver radiation extremely accurately to the target area while delivering very little radiation to normal tissues.  It is able to do this because instead of delivering the radiation at only a few different directions, it delivers the radiation during a complete 360 degree arc while continuously modifying the shape and intensity of the radiation beam.  

Since the device is designed around a CT scanner, it is able to do a CT scan each day before treatment delivery to verify that the target area is where it is expected to be.   If it isn't, the radiation treatment can be modified to adapt to changes in the position of the tumor and changes in the patient's anatomy (like weight loss) which is a technique called adaptive radiotherapy (ART). More details on diseases treated go here

The IMRT beam than travels around in a circular or helical fashion and accurately hits the tumor