Conformal radiotherapy and intensity-modulated radiotherapy - Clinical data

Conformal radiotherapy (CRT) is based on three hypotheses: (i) a higher rat e of local control can improve the survival rate; (ii) dose escalation can increase tumor control: and (iii) CRT allows the delivery of higher doses b y decreasing the incidence of late effects. These postulates are nov: suppo rted by several data. Three-dimensional conformal radiotherapy (3D-CRT) has markedly progressed since its introduction two decades ago. However, there are situations for which 3D-CRT cannot produce a satisfactory treatment pl an because of complex target volume shapes or the close proximity of sensit ive normal tissues. This is why intensity-modulated radiation therapy (IMRT ) was introduced. Its aim is to overcome the limitations of 3D-CRT by addin g modulators of beam intensity to beam shaping. IMRT can achieve nearly any dose distribution; however. the role of the planner remains crucial. CRT h as been investigated mainly for prostate cancers and head and neck cancers. By and large, the clinical data, although still limited, seem to confirm t he advantages of this type of radiotherapy. Dose escalation in prostate can cers improves the local control rate without increasing late effects and fo r this cancer site IMRT appears to be a significant advance over convention al 3D-CRT. In head and neck cancers the clinical data are still scarce but encouraging. CRT should be investigated in breast cancers with the aim of r educing the incidence of late effects. The available data underline the gre at potential for major progress in 3D-CRT and IMRT. The techniques are stil l costly and time consuming, nevertheless they merit investigation since th eir cost should decrease. Efforts should be concentrated on the specificati on of robust optimization criteria, taking into account clinical and radiob iological data.