IMRT: GENERAL CONSIDERATIONS
Schulz (1999a) has based his argument against conformal radiotherapy on the view that an improved cure could not be demonstrated to justify increased cost and complexity. His opinion has been challenged by Mohan et al (1999) who claims that there is evidence for increased cure, e.g. in the prostate against measurable (PSA change) criteria. They also argue that the development of new techniques would, at minimum, allow the generation of more data to support the dose-escalation hypothesis. They further argue for CFRT as a form of conformal avoidance whereby normal structures are saved even if there can be no demonstrable improvement in tumour control. They plead for an understanding
Figure 1.2. (a) This shows a 3D rendering of the volume of the prostate, the adjacent bladder and rectum, which are OARs when treating the prostate. The rendering is formed in the planning system VOXELPLAN from contours in a series of transaxial slices created by CT scanning. It is clear that the concave nature of the surface of the prostate and the close proximity of the rectum in particular requires a concave dose distribution to be delivered to the prostate. This would not be obtained from the unmodulated field-shapes shown. Intensity-modulation is called for. (b) A similar clinical case viewed laterally extracted from the VOXELPLAN planning system.