Tomotherapy: A new concept for the delivery of dynamic conformal radiotherapy

Tomotherapy, literally ‘‘slice therapy,’’ is a proposal for the delivery of radiation therapy with intensity‐modulated strips of radiation. The proposed method employs a linear accelerator, or another radiation‐emitting device, which would be mounted on a ring gantry like a CT scanner. The patient would move through the bore of the gantry simultaneously with gantry rotation. The intensity modulation would be performed by temporally modulated multiple independent leaves that open and close across the slit opening. At any given time, any leaf would be (1) closed, covering a portion of the slit, (2) open, allowing radiation through, or (3) changing between these states. This method would result in the delivery of highly conformal radiation. Overall treatment times should be comparable with contemporary treatmentdelivery times. The ring gantry would make it convenient to mount a narrow multisegmented megavoltage detectorsystem for beam verification and a CT scanner on the treatment unit. Such a treatment unit could become a powerful tool for treatment planning, conformal treatment, and verification using tomographic images. The physical properties of this treatmentdelivery are evaluated and the fundamental design specifications are justified.