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 treatment delivery times. The ring gantry would make it convenient to mount a narrow multisegmented megavoltage detector system 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 treatment delivery are evaluated and the fundamental design specifications are justified.

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An efficient method of calculating dose distributions in homogeneous media for megavoltage photons is described. The method is similar to filtered backprojection image reconstruction and is based on the analogy between external beam radiotherapy and SPECT image reconstruction. The filtered backprojection dose calculation significantly reduces the computation time for a large number of x-ray beams compared to a conventional convolution dosimetry method. A factor of 20 reduction in computation time is demonstrated for a 2D implementation of the model. The method has proved useful for speeding up an inverse treatment planning algorithm for conformal radiotherapy, and has the potential to be implemented in the reconstruction hardware of a radiotherapy CT simulator. Results of computer simulations based on the model are presented.

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