Purpose: Prostate cancer is one of the most common malignant cancers. Several radiotherapy planning methods have been suggested for the treatment of prostate cancer. In this study, four-field, and Field-In-Field (FIF) planning methods were compared based on dosimetric parameters. Materials and Methods: In the radiotherapy Treatment Planning System (TPS) for 10 patients who were treated with the common four-field method, the planning was also performed by the FIF method. Dosimetric parameters were measured for Planning Target Volume (PTV), rectum, and bladder. These parameters included maximum dose, minimum dose, mean dose, V15%, V25%, V30%, and V35%, as well as Homogeneity Index (HI) and Conformity Index (CI). Two treatment planning methods based on dosimetric parameters were compared using paired t-test. Results: Maximum, minimum and mean dose in PTV, rectum, and bladder were significantly different for the two techniques. There was no significant difference between the two planning techniques in dosimetric parameters of V15%, V25%, V30%, and V35% for rectum and bladder. The FIF technique delivers more doses to the tumor. HI was better in the FIF method than in the four-field method, but CI was not significantly different. In both techniques, the rectum and bladder did not receive doses above 60 Gy. Conclusion: In the treatment of prostate cancer in both Four-field and FIF planning methods, the dose to the rectum and bladder is less than the tolerance dose. FIF technique is recommended to better control the tumor. Based on dosimetric parameters, no significant findings were obtained that prove the superiority of FIF over the four-field technique in the treatment of prostate cancer.
