THE PRESENT study aims to evaluate three dimensional …...conformal radiation therapy (3DCRT) for patients with prostate cancer. This will be done by the effect of 6 MV and 15 MV photon energies in addition to some of treatment fields using different of conformity indices. For such study 10 patients with prostate cancer are selected. The computed tomography CT slices are taken for each patient and transferred to XiO treatment planning system. Evaluation of treatment plans is performed by conformity indices. The 3DCRT plans are designed using CMS XiO treatment planning system using linear accelerator with multi-leaf collimator (MLC) with two energies 6 and 15 MV. The results of conformity index (CI) show anaverage value from 1.5± 0.03 to 1.9± 0.06 in 6-Fields with 15 MV and 3-Fields with 6MV, respectively. The results of conformation number (CN) indicate an average value from 0.51± 0.02 to 0.67± 0.02 in 3-Fields  with 6MV and 6-Fields with 15MV, respectively. In conclusion, the use of high-energy 15 MV or 6 MV photons achieves the same dose coverage but in case of using 15 MV photon produces better safety for organs at risk and also improves conformity indices of dose to planning target volume (PTV). This occurs when increasing number of fields which improves conformity indices and decrease dose to organs at risk. The conformity index and conformation number give the same dosimetric information after the revision of DVH and dose distributions.