Abstract: Objective To compare the dose distribution of the threedimensional conformal radiotherapy（3D-CRT）and conventional radiotherapy plan and explore the value of 3DCRT in postorchiectomy radiotherapy for stage I testicular seminoma. Methods After 12 cases diagnosed with stage Ⅰ testicular cell tumors received high inguinal orchiectomy. And then postoperative radiotherapy were performed. 3DCRT plan and virtual conventional treatment plans（VCP）were performed for each patient by the treatment planning systerm（TPS）.The conformal index（CI），heterogeneity index（HI）of each planning target volume（PTV）and the dose of normal organs were analyzed with the dose volume histogram（DVH）.
ResultsThe CI values of PTV were 0.82±0.05 and 0.88±0.06 in VCP and 3D-CRT，respectively.The HI values of PTV were 0.29±0.11 and 0.15±0.03，respectively.3D-CRT was superior to VCP（P＜0.05）. The irradiation volum（IV） of 3D-CRT was lower than that of VCP（5268.20±1018.60cm³ vs. 5970.24±1471.49cm³，P＜0.05）. As the mean dose and the ratio of dose volume V15 on the small intestine，3D-CRT was lower than virtual conventional treatment plans（P＜0.05）. The mean dose of testis in 3D-CRT was lower than virtual conventional treatment（P＜0.05）.
Conclusion Conventional radiation field is determined according to the signs of the patient's bone， not necessarily suitable for each patient， while the 3D-CRT is more individualized.3D-CRT is superior to VCP in both dose conformal degrees and dosimetry homogeneity， meanwhile reducing the dose and the volume of the small intestine and testis. Whether these dosimetric advantages can be converted into clinical benefit needs further clinical experiments.