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Objective: To evaluate the potential benefit of carbon ion radiotherapy (C-ion RT) through comparison with photon intensity-modulated radiotherapy (IMRT) in dose distribution for prostatic adenocarcinoma., Methods: In randomly selected 5 patients, treatment planning of C-ion RT (4 coplanar beams) and IMRT (7 coplanar fields) were worked out by computer working station. In order to make a meaningful comparison, it was defined that the 95% isodose surface had to cover 100% of the PTV in each plan; all dose was given as normalized dose with the definition of the minimum dose of the PTV being equal to 95% of prescribed dose. Dose-volume histograms (DVHs) of the tumor and organ-at-risks (OARs) were calculated. Volume irradiated more than or equal to some specified doses, conformity index ( CI) , and inhomogeneity coefficient (IC) of each treatment plan was compared, respectively., Results: With C-ion RT, the mean irradiated volumes (in %) of the rectum were significantly smaller than that with IMRT except for 95% dose level, and C-ion RT could provide complete protection to the posterior rectal wall. In addition, C-ion RT could also remarkably reduce the dose to the bladder, femoral heads and non-target normal tissues at each dose level. Dose conformation and homogeneity in the target volume of C-ion RT were better than that in IMRT (mean CI50%, 3.36 vs. 5.04, mean CI95%, 1.20 vs. 1.46, mean IC, 0.03 vs. 0.12)., Conclusion: Compared with IMRT, C-ion RT can obtain better dose distribution, and may reduce tumor recurrence and radiation-induced complications in prostatic adenocarcinoma.