| Objective: To compare the dosimetric advantages and disadbantages between intensity modulated radiotherapy (IMRT) and conventional three- dimensional conformal radiotherapy of nasopharyngeal carcinoma (NPC), lung cancer and rectal cancer.To give doctors some suggestions when they choose plans for patients.Materials and Methods: From june 2009 to February 2010, 35 patients were enrolled to this study, 10 patients were diagnosed nasopharyngeal carcinoma,13 patients were diagnosed lung cancer, 12 patients were diagnosed rectal cancer. All the patients got CT-sim scan, then the image was delived to the TPS.Every patient was simultaneously performed two plans, that is IMRT and 3D-CRT. The dose prescription for the same disease is the same one despite the stage of the disease is different.It is convenient to analyze the dose distributions.The comparison is divided into two aspect, the target dose and dose of organ at risk. The tools we used are dose profile and DVH (Dose-volume Histograms).Evaluation Indexes: Target: Dmin, Dmax, Dmean, CI (Conformity index), HI (Heterogeneity index) etc.Organ at risk: Dmin, Dmax, Dmean, Vx etc.Results: For NPC, The Dmax, Dmean, CI, HI were as follow (IMRT/3D-CRT). PGTV: 76.56Gy/76.86 Gy, 72.34 Gy /71.14 Gy, 1.22/1.43, 1.23/1.16.PTV1: 74.19 Gy /76.51 Gy, 70.76 Gy /68.34 Gy, 1.21/1.38, 1.40/1.28.PTV2:66.85 Gy /52.74 Gy, 52.34 Gy /46.68 Gy, 1.18/0.49, 1.21/1.68. Brain stem:Dmax, Dmean46.61 Gy /55.24 Gy, 26.89 Gy /20.57 Gy.lens: Dmax5.77 Gy /3.05 Gy.Optic nerve: Dmax, Dmean50.52 Gy /49.82 Gy,35.97 Gy /36.27 Gy.Optic chiasm:Dmax53.10 Gy /44.16 Gy.Spinal cord:Dmax, Dmean39.90 Gy /45.82 Gy, 36.38 Gy /37.50 Gy. parotid gland-R:Dmax, Dmean, V30, 71.56 Gy /75.75 Gy, 39.89 Gy /65.83 Gy,60.80 /99.50. parotid gland-L: Dmax, Dmean, V30, 72.64 Gy /75.63 Gy, 37.88 Gy /66.50 Gy, 60.60/99.60. For lung cancer: Target:Dmax, Dmean, CI, HI, 68.36 Gy /67.89 Gy, 63.86 Gy /63.65 Gy, 1.28/1.90, 1.31/1.14.lung-all: Dmean, V20, 19.29 Gy /22.13 Gy, 36.80/37.00.Spinal cord:Dmax, Dmean42.29 Gy /43.49 Gy, 24.75 Gy /23.15 Gy. Heart: Dmean, V50, 20.01 Gy /20.93 Gy, 6.80/9.90. For rectal cancer: Target: Dmax, Dmean, CI, HI, 55.59 Gy /55.24 Gy, 52.70 Gy /52.30 Gy, 1.21/1.42, 1.24/1.11.Bladder: Dmax, Dmean, V50, 53.70 Gy /52.42 Gy, 34.08 Gy /42.30 Gy, 7.25/51.60. Femoral head: Dmax, Dmean, V50, V40, 44.43 Gy /44.87 Gy, 23.88 Gy /40.16 Gy, 0/0, 1.41/29.20.Conclusions: ntensity Modulated Radiotherapy (IMRT) is a better technology compared with 3D-CRT, the target dose distribution and the protection of organs at risk is better than 3D-CRT. NPC is very suitable for IMRT, rectal cancer can also use IMRT.But for lung cancer, target movement is very significant, so only in a very good image-guided techniques (such as respiratory gating technology) circumstances we can consider using.
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