In intensity modulated radiation therapy (IMRT)

an approach to generate uniform photon beams is to use electron pencil beams to bombard a set of points that are discretely arranged on the target. It was considered that the E-beam energy in this technique should be greatly higher than that those from accelerators commonly available for radiation therapy. In this study

Monte Carlo simulation was used to explore the possibility of generating the needed photon fluence distribution by using a common medical accelerator. The fluence distributions produced by electrons pencil beam in different energies were compared. Optimal target materials

and the geometry

were determined. The photon fluence distributions of wide fields at various target point intervals were simulated for suitable density of the target points. Two fluence distributions in common request by conventional IMRT were taken as examples to show that the desired fluence distributions could be achieved by optimizing the intensity of electron beam on target points.