الفهرس 
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Abstract
Radiation therapy treatment means giving the cancer tumor radiation dose which is prescribed accurately at the same time protecting normal tissues (organ at risk) surrounding the tumor from exposure to radiation. This study was aimed to study the effects of low- and high-energy intensity-modulated (IMRT) photon beams on the planning of target volume and the critical organs in cases of prostate cancer. Materials and Methods: the plans were generated using either 6 MV or 15 MV alone, and both 6 and 15 MV beams. For each plan generated using suitable planning objectives and dose constraints, which was set to be identical except then beam energy. The plans were analyzed in terms of target coverage, conformity, and homogeneity regardless of beam energy.Results: Mean percentage of V 70Gy of rectal wall in 6 MV, 15 MV and mixed-energy plans was 16.9%, 17.8%, and 16.4%, respectively, while the mean percentage of V 40Gy was 53.6%, 52.3%, and 50.4%. The mean dose to femoral heads in 6 MV, 15 MV, and mixed-energy plans were 30.1 Gy, 25.5 Gy, and 25.4 Gy, respectively. The integral dose of 6 MV plans was 10% (on average) larger than those of 15 MV or mixed-energy plans. Conclusion: The preliminary results suggested that mixed-energy IMRT plans may take an advantage of the dosimetric characteristics of low- and high-energy beams, in this study, mixing energy in an IMRT plans showed better OAR sparing and for deep-seated tumors, the overall plan quality was improved.