center of spinal cord (CSC; 2-3 mm diameter ROI at geometric center of the cord) were calculated for all patients. Median follow-up was 66 months (range: 13-160 months). Toxicity was scored according to the Common Toxicity Criteria of Adverse Events (CTCAE v4.03). Descriptive and linear regression analyses were performed. Results: Patients received a mean Dmax / D2% to the spinal cord of 59 Gy (RBE) / 55 Gy (RBE) and to the CSC of 52 Gy (RBE) / 51 Gy (RBE), respectively. Four patients (6%) developed acute radiation-induced neurologic toxicity (Grade 1: nZ1, Grade 2: nZ3). Seventeen percent of patients experienced minor late neurologic toxicities (Grade 1: nZ7, Grade 2: nZ4). Of these patients, 4 developed Lhermitte's syndrome. One patient experienced Grade 4 toxicity (tetraplegia) after receiving 58 Gy (RBE) to the surface and 54 Gy (RBE) to the CSC (SC: V45 11.8 cc, V50 9.35 cc; CSC: V40 3.17 cc, V45 3.1 cc). Of note, the patient was considered high-risk due to postoperative, transient tetraparesis prior to PBSPT and potential spinal instability with a narrow canal. On final analysis, no significant correlation was found between spinal cord Dmax, CSC Dmax, or length of CTV and toxicity. However, higher CSC Dmax and longer CTV tended to correlate with Grade 2 neurologic toxicity, but this was not statistically significant. Conclusion: PBSPTwith spinal cord doses of up to 60 Gy (RBE) to the surface and 50 Gy (RBE) to the center is associated with minimal spinal toxicity. In our experience, doses up to 64 Gy (RBE) to the surface of the spinal cord are deemed acceptable if unavoidable in achieving adequate tumor coverage.
To investigate the clinical efficacy and treatment toxicity of simultaneous integrated boost (SIB) intensity-modulated radiotherapy (IMRT) in nasopharyngeal carcinoma (NPC). Materials/Methods: Between Aug. 2009 and Dec. 2014, 219 consecutive non-metastatic NPC patients were treated with SIB-IMRT with or without combination of cisplatin-based chemotherapy at our institution. The stage distribution was I: 12.4%, II: 20.5%, III: 30.6%, and IV: 36.5%, respectively. The prescribed dose of high, middle and low risk area of plan target volume was 69.96 or 69.3 Gy, 59.4 Gy, and 52.8 Gy in 33 fractions, respectively. Acute and late toxicities were evaluated according to Common Terminology Criteria for Adverse Events version 4.0. Cox model was used to screen the prognostic factors of locoregional failure (LRF), distant metastasis (DM) and overall survival (OS). Results: The median follow-up period was 42.4 months (range, 2.0-83.7 months). The 3-year actuarial LRF, DM, and OS rates were: 8.9%, 11.2%, and 87.4%, respectively. Cox regression analysis revealed stage T3-T4 to be an independent predictor for poor OS {HR: 2.7 [95% confidence interval (CI): 1.3-5.5]}; and N2-N3 to be independent predictors for a greater likelihood of LRF (HR: 9.0, 95% CI: 2.0-40.3), DM (HR: 2.9, 95% CI: 1.1-7.4), and poor OS (HR: 4.6, 95% CI: 1.9-11.4). Acute dermatitis and mucositis ! grade 3 occurred in 5.5% and 14.2% of patients, respectively. The 3 year cumulative incidence of ! grade 3 late toxicities was 5.7%.
Conclusion:Our results prove that SIB-IMRT for the primary treatment of NPC achieved high locoregional control with a favorable acute/late toxicity profile.
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