Acute toxicity in nasopharyngeal carcinoma patients treated with IMRT/VMAT.

PURPOSE: To evaluate acute toxicity in nasopharyngeal cancer (NPC) patients treated with intensity modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) with or without cisplatin-based chemotherapy. MATERIALS AND METHODS: A total of 45 newly diagnosed, histologically proven non-metastatic NPC patients treated with IMRT between May 2010 and December 2012, were evaluated retrospectively, 37 planned with Eclipse and 8 with Prowess Panther treatment planning system. The doses to the planning target volumes of primary tumor and involved lymph nodes, high risk region, and uninvolved regional nodal areas were 70 Gy, 60 Gy, and 54 Gy respectively and delivered simultaneously over 33 fractions to 39 patients. Another 6 patients irradiated with sequential boost technique. Some 84.4% of patients received chemotherapy. Acute toxicities were graded according to the Radiation Therapy Oncology Group scoring criteria and Common Terminology Criteria for Adverse Events (CTCAE) for chemotherapy side effects. RESULTS: Median age was 43 years (14-79) and all patients were WHO type II. Grade 1 mucositis and dysphagia were observed in 17 (37.8%), and 10 (22.2%) patients, respectively. The incidence of acute grade 2 mucositis and dysphagia was 55.6% and 68.9%, respectively. The most common chemoradiotherapy related acute toxicities were nausea, leucopenia and thrombocytopenia. Grade 3 toxicity was detected in 13 (28.8%) cases. No grade 4 toxicity was occurred. Mean weight loss was 9%. None of the patients required the insertion of percutaneous endoscopic gastrostomy for nutritional support. Radiation therapy was completed without interruption in all patients. CONCLUSIONS: IMRT is a safe and effective treatment modality, and well tolerated by patients in the treatment of nasopharyngeal carcinoma. No unexpected side effects were observed.

Dosimetric evaluation of nasopharyngeal carcinomas irradiated with different IMRT techniques.

PURPOSE: To evaluate the performance of volumetric arc therapy (VMAT), dynamic intensity modulated radiotherapy (IMRT) and step-and-shoot IMRT techniques in nasopharyngeal cancer (NPC) patients. METHODS: IMRT plans of 48 NPC patients treated between May 2010 and December 2012, were evaluated. Twenty two patients were planned with VMAT, 18 with dynamic IMRT and 8 with step-and-shoot IMRT. Conformity index (CI) and homogeneity index (HI), the dosimetry of the planning target volumes (PTVs) and organs at risk (OARs) and the monitor units (MU) were evaluated for each IMRT modality. RESULTS: The conformity indices of VMAT and dynamic IMRT were better than step-and-shoot IMRT plans (p<0.05). Step-and-shoot IMRT plans provided better homogeneity than VMAT (p=0.01). MUs for dynamic IMRT were much higher compared to VMAT (p<0.01) and step and- shoot IMRT (p<0.01). There was no significant difference between the 3 techniques in terms of PTV70 mean doses. When compared with step-and-shoot IMRT, VMAT and dynamic IMRT had a better sparing effect on optic nerves, eyes and optic chiasm (p<0.05). VMAT plans performed better sparing for brain stem than dynamic IMRT (p=0.01). There was a remarkable decrease in the maximum doses of VMAT to the eye. CONCLUSIONS: VMAT outperforms dynamic IMRT by effectively reducing the MU and the dose to some OARs, with adequate PTV coverage. Also, VMAT provides better sparing of normal tissue and conformity than step-and-shoot IMRT. Differences between step-and-shoot IMRT and dynamic IMRT are thought to be due to technical differences of linear accelerator devices like fiber size, variable fiber, dose rate and gantry.