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Helical tomotherapy is an integrated therapeutic technique that includes planning, delivery and verification capabilities. Helical tomotherapy allows for irradiation of a large number of targets and region at risk (RAR) over broad regions of the body; a large-scale optimization technique is necessary. Usually a tomotherapy treatment will have tens to hundreds of thousands of pencils beams for which intensity needs to be optimized. Moreover the number of voxels where the dose needs to be computed is on the order of 1,000,000. The complexity and size of the optimization is the price paid in tomotherapy in order to obtain coplanar deliveries that are neither limited by the number of beam directions nor the degree of modulation used during delivery. It is important to note, however, that because of the simplicity and capabilities of the tomotherapy concept, a complex optimization plan will not lead to a complex delivery. The complexity of delivery is almost independent of the complexity on the optimization. In this work 4 clinical conformal and conformal avoidance optimization cases are be shown. Breast, prostate, mesothelioma and nasopharyengeal cases are presented and compared with some of the standard techniques used currently distributions and DVH's are shown to illustrate examples of the deliveries that can be achieved. The flexibility obtained to optimize both conformal and conformal avoidance treatments is also discussed.

Dose reconstruction (DR) is a radiotherapy process in which the full three-dimensional dose actually delivered to a patient is computed. The calculation is performed on a CT of the patient in the actual treatment position using the actual energy fluence obtained from delivery verification (DV). This provides valuable information regarding the efficacy of a treatment. Specifically, this is the basis for fraction-by-fraction adaptive radiotherapy. However, dose reconstruction is only as accurate as the inputs to the computation, namely the verified fluence and the CT. Studies were conducted regarding the effects of positional errors and internal anatomy changes for a canine nasopharyngeal treatment and a prostate treatment on an abdominal phantom, respectively. It was found that energy fluence errors may or may not be detected in DV. However, even if an error was detected, the authors show that the potential effects on outcome could not possibly be addressed without a CT at the time of delivery.

The Low-Energy Photon-Scattering (LSCAT) expansion to the EGS4 Monte Carlo code has been applied to the "scatter sphere" EGS4 code scasph.mortran to compute energy deposition kernels at photon energies below 100 keV. The LSCAT routines were used to replace the default atomic form factor and cross-section data used by EGS4 to model coherent scatter with measured molecular form factor and cross-section data. Energy deposition kernels were calculated with: (1) coherent scatter effects neglected, (2) coherent scatter effects included using the default EGS4 atomic form factor, and (3) coherent scatter effects included using the molecular form factor. These energy deposition kernels were utilized in a convolution/superposition code developed for mega-voltage therapeutic X-rays modified to compute dose at low photon energy. Depth dose calculations were made for 30 keV photons, where the coherent scatter contribution is maximum, using kernels which model coherent scatter in each of the three ways described. These calculations show a difference between the kernel that neglects coherent scatter compared to the kernels that include coherent scatter, but show no distinction between the atomic and molecular form factor kernels. A separation of the kernels into their primary and scatter components reveals that the depth dose calculation is dominated by the primary component. An examination of the kernels separated into their primary and scatter components suggest that the "scatter sphere" EGS4 code includes the coherent scatter contribution in the primary component of the kernel.

A calibration of the University of Wisconsin Tomotherapy Benchtop megavoltage CT (MVCT) system was investigated. It was found that IMVCT values correlate extremely well with electron density and that unlike kilovoltage CT, this correlation is well maintained for higher atomic number materials, and is more robust for different patient sizes and locations. Thus, small improvements in dosimetric calculations should be possible by deriving input images from MVCT as opposed to kVCT, as well as calibrating in terms of electron density, as opposed to physical density.