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 (D-max), mean dosage (D-mean) and minimum dosage (D-min) 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 V-10 similar to V-20 between 5-field and other fields (P < 0.05), but were similar in V-25 similar to V-30 (P > 0.05). However, 7-and 9-fields were similar in V-10 similar to V-20 (P > 0.05). Conclusion: 7-field IMRT plan is the optimal one for NPC on both clinical dosimetric requirements and field-establishment principles.