中文摘要：

目的：探索一种新的混合固定野调强（intensity-modulated radiation therapy,IMRT）和容积旋转调强（volumetric modulated arc therapy,VMAT）的放疗技术（hybrid-VMAT,H-VMAT）治疗颈椎原发恶性肿瘤的剂量学特点。方法：选择13例曾接受放射治疗的颈椎原发恶性肿瘤患者,分别设计七野IMRT、双弧VMAT和H-VMAT计划,H-VMAT计划结合单弧VMAT和5个固定角度调强野。通过与IMRT和VMAT比较,评价H-VMAT技术计划质量和实施效率。结果：H-VMAT、IMRT和VMAT技术PTV平均适形指数分别为0.75、0.67和0.80,平均均匀性指数分别为0.38、0.38和0.38;PGTV平均适形指数分别为0.78、0.74和0.78,平均均匀性指数分别为0.06、0.05和0.06。脊髓平均D0%分别为41.78、40.70和42.42Gy,脊髓危及器官PRV平均D1%分别为44.92、44.48和45.39Gy。与IMRT相比,H-VMAT降低了黏膜V30和平均剂量（P=0.038,0.000）。H-VMAT降低了下颌骨的V30和平均剂量（P=0.048,0.000）,但V5无差异（P〉0.05）,甲状腺和腮腺V5、V30和平均剂量无差异（P〉0.05）;与VMAT相比,H-VMAT黏膜平均剂量有所增加（P=0.016）,甲状腺、腮腺和下颌骨的V5、V30和平均剂量无差异（P〉0.05）。三种技术得到的正常组织V5无差异（P〉0.05）,H-VMATV30和平均剂量低于IMRT（P=0.001,0.001）,但较VMAT稍高（P=0.042,0.000）。H-VMAT、IMRT和VMAT的平均机器跳数分别是872、1101和505MUs,平均治疗时间分别是4.77、5.26和3.44分钟。结论：与IMRT相比,新的H-VMAT技术明显改善了靶区适形度,降低了黏膜、下颌骨和正常组织中高剂量区照射体积（V30）和平均剂量,机器跳数明显下降;与VMAT相比,新的H-VMAT技术改善了脊髓的保护,平均机器跳数和治疗时间有所增加。

英文摘要：

Objective： To explore the dosimetric characteristics of a novel hybrid volumetric-modulated arc therapy（ H-VMAT） technique that combines intensity-modulated radiation therapy（ IMRT） and volumetric-modulated arc therapy（ VMAT） for the treatment of primary cervical spine malignant tumors. Methods： Thirteen patients with primary cervical spine malignant tumor underwent radiation therapy were enrolled in this study. Seven-beam IMRT,two-arc VMAT and H-VMAT plans were developed for each patient. The H-VMAT technique consisted of one full arc and five fixed angle intensity-modulated fields,which accounted for approximately half of the prescribed dose. Plan quality and delivery efficiency was compared for H-VMAT,IMRT and VMAT. Results： The mean conformity index of PTV（ Planning Target Volume） was 0. 75,0. 67 and 0. 80 for the H-VMAT,IMRT and VMAT plans. The mean homogeneity index was 0. 38,0. 38 and 0. 38,respectively. The mean conformity index of PGTV（ Planning Gross Tumor Volume） was 0. 78,0. 74 and 0. 78,respectively. The mean homogeneity index was 0. 06,0. 05 and 0. 06,respectively. The mean maximum dose（ D0%） of spinal cord was 41. 78,40. 70 and 42. 42 Gy for the H-VMAT,IMRT and VMAT,respectively. The mean maximum dose（ D1%） of spinal cord PRV（ Planning Organs at Risk Volume） was 44. 92,44. 48 and 45. 39 Gy,respectively. V30 and mean dose of mucosa and mandible decreased in H-VMAT compared with IMRT（ P = 0. 038,0. 000 and P = 0. 048,0. 000,respectively）,but no significant difference was found in V5（ P 0. 05）. No significant difference was found in V5,V30 and mean dose of thyroid glands,parotid glands and mandible compared H-VMAT with VMAT（ P 0. 05）,except that the mean dose to mucosa was a little higher in H-VMAT（ P = 0. 016）. For normal tissue sparing,V30 and mean dose of H-VMAT was lower than those of IMRT（ P = 0. 001,0. 001）,but slightly higher than those of VMAT（ P = 0. 042,0. 000）. The difference in V5 to normal tissue was statistically not significa