Effect Of Beam Orientation On Acute Complications In Intensity-modulated Radiation Therapy Of Nasopharyngeal Carcinoma

[Objective]The aim of this study was to compare two different beam arrangements in the treatment plan of intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC) and its acute complications to find a reasonable beam arrangement.[Methods]Twenty NPC patients were randomly selected in the study. Philips Pinnacle Planning System8.0was chosen to design the IMRT plan. Ten of the20patients were treated by the IMRT-7P plan, which was planned by the hind half-planes of seven fields of the IMRT plan. The remaining10patients were treated by the IMRT-7A plan, which was planned by seven equi-spaced fields of the IMRT plan. Then, the plans of homologous hind half-plane and equi-spaced fields were re-planned. Dosimetric comparisons between IMRT-7P and IMPT-7A were conducted to evaluate the coverage, homogeneity index (HI), and conformity indexes (CI) of the planning target volume (PTV) and organs at risk sparing (OARs). Acute complications of the patients in the two groups were observed and compared during radiotherapy.[Results]IMRT-7P and IMRT-7A had a similar PTV coverage. No significant differences in HI and CI between IMRT-7A and IMRT-7P were observed. However, in the aspect of OARs, IMRT-7P had a better sparing effect on the brain stem, cord, parotid gland, and sub-mandibular gland (P<0.05) to a certain extent, especially on oral cavity where IMRT-7P plan had significantly lower pertinent parameters compared with that of IMRT-7A [DMEAN:(29.3±1.3) Gy, and (35.7±2.3) Gy,P<0.01; V30:(36.2±5.4)%, and (73.1±10.9)%,P<0.01; V40:(13.3±3.8)%, and (29.0±9.7)%,P<0.01]. In the aspect of acute complications, such as xerostomia, acute oral mucositis, skin injury, and weight loss, patients who were treated by IMRT-7P achieved a better curative effect compared with those treated by IMRT-7A (P<0.05).[Conclusion]IMRT-7P plan for NPC can reduce the dose delivered to OARs to a certain extent and can better protect the normal tissue around the target. In addition, the IMRT-7P plan can better relieve acute complications of radiotherapy compared with the IMRT-7A plan.