Radiation treatment planning for prostate cancer: A new dosimetric comparison of five and seven fields IMRT plans

Background: To compare the dosimetric coverage of the planning target volume (PTV) and the dose delivered to the main Organs at Risk (OARs) in 5 and 7-field techniques of Intensity Modulated Radiation Therapy (IMRT) in patients with local prostate cancer. Materials and Methods: Twelve patients with local prostate cancer underwent 5 and 7-field IMRT planning. The delivery of IMRT was carried out using the sliding technique. The dose coverage for PTV was designated to ≥98% of the PTV covered by 95% of the prescribed dose. Dose conformity was evaluated by comparing the volume of nontarget tissue receiving maximum, and average of the prescribed dose and the dose of 33%, 50%, and 66% of the volumes on both planning sets. For target, this evaluation was made with comparing the Conformity Index (CI) and Inhomogeneity Index (HI). In addition, we compared the monitor units used for dose delivery in both planning techniques. Results: All the 5 and 7-field IMRT plans differed slightly in the measured parameters, and none of them have statistically significant differences with each other except for the monitor units where significant differences were observed in favor of the 5-field IMRT plans (p=0.000). In all of the 5-field IMRT plans the mean dose delivered to OARs were very similar or less than that of the 7-field plans. Conclusion: In comparison to the 7-field technique, the 5-field IMRT technique has resulted in improved IMRT dose conformity, homogeneity, and lesser MUs used for radiation therapy. However, this difference was not significant.