TomoTherapy and Radixact (helical radiotherapy)

TomoTherapy grew out of work at the University of Wisconsin in the 1990s and treated its first patients in the early 2000s. A 6 MV linac is mounted on a CT-style ring gantry that rotates continuously while the couch advances, and a binary multileaf collimator opens and closes each leaf in fractions of a second to modulate a fan beam, so the dose is laid down helically. Before each fraction the same beam at low output produces a megavoltage CT for positioning. Because the field of view runs the length of the couch travel, it treats craniospinal axis, total marrow irradiation before transplant, long spinal or pelvic volumes and multiple targets without field junctions, and it gives highly homogeneous head and neck plans. The current Radixact generation adds Synchrony, which tracks tumour motion with kilovoltage imaging and moves the beam with it, and kilovoltage CT for better image quality.

Against a C-arm linac it offers no electrons, no non-coplanar beams and a single photon energy, treatment can be slow for large volumes, and departments need staff comfortable with a distinct planning system. Accuray, which also makes the CyberKnife, is the sole vendor.