Clinical Dosimetric Comparison among Different Intensity-Modulated Radiotherapy Plans for Nasopharyngeal Carcinoma

Objective: To compare the dosimetric differences of different intensity-modulated radiation therapy (IMRT) plans for nasopharyngeal carcinoma (NPC). Methods: 5-, 7- and 9-fields of IMRT plans in 16 NPC patients were respectively designed and synchronous dimention technology was applied to compare the dosimetric differences in target areas and involved organs. Results: The recovery rate in target area was 95% while the plan was evidently worse in 5-field than in 7- and 9-fields (P ＜ 0.05). Whereas the maximum dosage (Dmax), mean dosage (Dmean) and minimum dosage (Dmin) were similar between 7- and 9-fields (P ＞ 0.05), which were obviously lower in 5-field, and the differences were both significant (P ＜ 0.05). In addition, the conformity and homogeneity indexes in target area had no significant difference between 7- and 9-fields, but were markedly better than in 5-field (P ＜ 0.05). Indexes in each involved organs were the lowest in 5-field than in other fields (P ＜ 0.05), but were similar between 7- and 9-fields (P ＞ 0.05), which were all lower than tolerant dosage. As for BODY, there were significant differences in V10 - V20 between 5-field and other fields (P ＜ 0.05), but were similar in V25 - V30 (P ＞ 0.05). However, 7- and 9-fields were similar in V10 - V20 (P ＞ 0.05). Conclusion: 7-field IMRT plan is the optimal one for NPC on both clinical dosimetric requirements and field-establishment principles