Image Correlation and In Vivo Dosimetry in IMRT

Intensity modulated radiation therapy is pushing the frontiers of radiation therapy in several different areas simultaneously. Broadly speaking, these areas are (a) the dose calculation algorithms, (b) the use of inverse planning or plan optimization algorithms, (c) the complexity of the treatment plan in terms of the large increase in the number of variables that define the treatment, and (d) the enlarged scope of manufacturer-provided software needed to deliver the entire treatment. These advances are, of course, not independent. The optimization algorithms produce fluence distributions that result in a large number of time-dependent variables being required. In turn, this increase in the number of states of the delivery needing to be modelled (such as leaf edge penumbra at nearly every point within the field) has required a more sophisticated dose calculation algorithm, since relatively small errors per field become much more important with so many segments. And finally, the large number of variables results in the need for computer control of the treatment delivery since no person could manage the complexity.