Assessment and Comparison of Homogeneity and Conformity Indexes in Step-and-Shoot, Compensator-Based Intensity Modulated Radiation Therapy (IMRT) and Three-Dimensional Conformal Radiation Therapy (3D CRT) in Prostate Cancer

Abstract

Introduction: Intensity modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D CRT) are two treatment modalities in prostate cancer, which provide acceptable dose distribution in tumor region with sparing the surrounding normal tissues. IMRT is based on inverse planning optimization; in which, intensity of beams is modified by using multileaf collimators and also compensators with optimum shapes in step and shoot (SAS) and compensator-based method, respectively. Materials and Methods: Prescribed dose was 80 Gy for both IMRT procedures and 70 Gy for 3D CRT. Treatment plans of 15 prostate cancer candidates were compared to target the minimum dose, maximum dose, V 76 Gy (for IMRT plans) V 66.5 Gy (for 3D CRT), mean dose, conformity index (CI), and homogeneity index (HI). Results: Dose conformity in compensators-based IMRT was better than SAS and 3D CRT. The same outcome was also achieved for homogeneity index. The target coverage was achieved 95% of prescribed dose to 95% of planning target volume (PTV) in 3D CRT and 95% of prescribed dose to 98% of PTV in IMRT methods. IMRT increases maximum dose of tumor region, improves CI and HI of target volume, and also reduces dose of organs at risks. Conclusion: Results of this study showed that both IMRT methods provide better target coverage in comparison of 3D CRT. In SAS technique, maximum dose reduced compared with compensator-based IMRT while, in the later method, CI and HI improved; it must be mentioned that 3D CRT also had the acceptable HI and CI results. IMRT approaches represented better homogeneity and conformity over 3D CRT and in comparison of two IMRT methods, all acceptable results can be achieved in compensator IMRT.