Treatment delivery accuracy in intensity-modulated conformal radiotherapy.

The importance of geometric and dosimetric inaccuracies in the delivery of conformal radiotherapy using intensity-modulated x-ray fields is assessed. It is shown that although the incident intensity or fluence profiles may have large gradients, the resulting absorbed dose profile gradients are shallower because of electron transport and photon scatter. This makes the interleaving of dose contributions from the many intensity-modulated fields used less critically dependent on their relative positions and on the accuracy of profile generation. It is found that the expected geometric and dosimetric inaccuracies do not make this technique impracticable provided that good patient fixation and beam delivery can be assured.