Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073, USA.
Radiother Oncol. 2010 May;95(2):153-7. doi: 10.1016/j.radonc.2009.12.039. Epub 2010 Jan 28.
PURPOSE/OBJECTIVE(S): Volumetric modulated arc therapy (VMAT) allows for intensity-modulated radiation delivery during gantry rotation with dynamic MLC motion, variable dose rates and gantry speed modulation. We compared VMAT plans with 3D-CRT for hypofractionated lung radiotherapy.
MATERIALS/METHODS: Twenty-one 3D-CRT plans for Stage IA lung cancer previously treated stereotactically were selected. VMAT plans were generated by optimizing machine aperture shape and radiation intensity at 10 degrees intervals. A partial arc range of 180 degrees was manually selected to coincide with tumor location. The arc was resampled down to 5 degrees intervals to ensure dose calculation accuracy. Identical planning objectives were used for VMAT/3D-CRT. Parameters assessed included dose to PTV and organs-at-risk (OAR), monitor units, and multiple conformity and homogeneity indices. Plans were delivered to a phantom for time comparison.
Lung V(20/12.5/10/5) were less with VMAT (relative reduction 4.5%, p = .02; 3.2%, p = .01; 2.6%, p = .01; 4.2%, p = .03, respectively). Mean/maximum-doses to PTV, dose to additional OARs, 95% isodose line conformity, and target volume homogeneity were equivalent. VMAT improved conformity at both the 80% (1.87 vs. 1.93, p = .08) and 50% isodose lines (5.19 vs. 5.65, p = .01). Treatment times were reduced significantly with VMAT (mean 6.1 vs. 11.9 min, p < .01).
Single arc VMAT planning achieves highly conformal dose distributions while controlling dose to critical structures, including significant reduction in lung dose volume parameters. Employing a VMAT technique decreases treatment times by 37-63%, reducing the chance of error introduced by intrafraction variation. The quality and efficiency of VMAT is ideally suited for stereotactic lung radiotherapy delivery.
容积调强弧形治疗（VMAT）允许在机架旋转时通过动态多叶准直器运动、可变剂量率和机架速度调制进行强度调制放射治疗。我们比较了立体定向治疗后早期肺癌的分割放疗的 VMAT 计划与 3D-CRT。
材料/方法：选择了 21 例先前接受立体定向治疗的 I 期肺癌的 3D-CRT 计划。VMAT 计划通过在 10 度间隔处优化机器孔径形状和辐射强度来生成。手动选择 180 度的部分弧形范围与肿瘤位置一致。弧形被重新采样到 5 度间隔以确保剂量计算的准确性。VMAT/3D-CRT 使用相同的计划目标。评估的参数包括 PTV 和危及器官（OAR）的剂量、监测单位和多个适形度和均匀性指数。计划被输送到体模进行时间比较。
VMAT 的肺 V20/12.5/10/5 更小（相对减少 4.5%，p =.02；3.2%，p =.01；2.6%，p =.01；4.2%，p =.03）。PTV 的平均/最大剂量、附加 OAR 的剂量、95%等剂量线适形度和靶区均匀性相当。VMAT 在 80%（1.87 比 1.93，p =.08）和 50%等剂量线（5.19 比 5.65，p =.01）上提高了适形度。VMAT 治疗时间明显缩短（平均 6.1 比 11.9 分钟，p <.01）。
单弧 VMAT 计划在控制危及器官剂量的同时，实现了高度适形的剂量分布，包括显著降低肺剂量体积参数。采用 VMAT 技术可将治疗时间减少 37-63%，降低分次内变化引入的误差机会。VMAT 的质量和效率非常适合立体定向肺放疗。
