Quantifying the effect of respiratory motion on lung tumour dosimetry with the aid of a breathing phantom with deforming lungs
Quantifying the effect of respiratory motion on lung tumour dosimetry with the aid of a breathing phantom with deforming lungs
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DOI：
10.1088/0031-9155/51/14/005
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发表时间：
2006-07-21
影响因子：
3.5
通讯作者：
Webb, Steve
中科院分区：
文献类型：
--
作者：
Nioutsikou, Elena;Symonds-Tayler, J. Richard N.;Webb, Steve
器官和肿瘤运动对呼吸肺放疗期间计划剂量分布退化的贡献已通过实验研究和量化。一个具有可变形肺部的拟人化、组织等效的呼吸模型已经建立，其中肺部肿瘤可以在任意 3D 轨迹上被驱动。轨迹被编程到运动控制器中，该运动控制器连接到与肿瘤相连的高精度移动平台。运动控制器连接到加速器的剂量计数器，运动速度与剂量率成比例。尽管剂量率或段间时间发生变化，这仍可确保一致的输送。在这项研究中，模型通过一组周期方程来呼吸，这些周期方程通过不对称的三角函数表示呼吸运动。选择几个运动幅度应用于运动的主轴。将具有不同起始阶段（在呼吸周期中均匀间隔）的五个三维几何共形 (3DCRT) 部分传送到体模，并与体模在呼气末位置静止时的传送进行比较。随后以相同的方式实施了一套调强放射治疗计划（IMRT）。运动幅度越大，剂量模糊程度越高。当故意错误地选择 PTV 时，会观察到严重的剂量不足，其程度与裕度误差程度相关。 IMRT 运动平均剂量分布在总肿瘤体积 (GTV) 中呈现出静态照射中不存在的高剂量区域，这些区域是由优化器创建的增强分段产生的，以便在逆向规划过程中实现规划靶体积 (PTV) 均匀性。另一方面，3DCRT 没有表现出这样的效果。结论是，即使已充分选择 PTV 裕度以包括呼吸运动的程度，在将 IMRT 递送至呼吸肺时也应注意控制递送的流量。
The contribution of organ and tumour motion to the degradation of planned dose distributions during radiotherapy to the breathing lung has been experimentally investigated and quantified. An anthropomorphic, tissue-equivalent breathing phantom with deformable lungs has been built, in which the lung tumour can be driven in any arbitrary 3D trajectory. The trajectory is programmed into a motion controller connected to a high-precision moving platform that is connected to the tumour. The motion controller is connected to the accelerator's dose counter and the speed of motion is scaled to the dose rate. This ensures consistent delivery despite variation in either the dose rate or inter-segment timing. For this study, the phantom was made to breathe by a set of periodic equations representing respiratory motion by an asymmetric, trigonometric function. Several motion amplitudes were selected to be applied in the primary axis of motion. Five three-dimensional, geometrically conformal (3DCRT) fractions with different starting phases (spaced uniformly in the breathing cycle) were delivered to the phantom and compared to a delivery where the phantom was static at the end-expiration position. A set of intensity-modulated radiotherapy plans (IMRT) was subsequently delivered in the same manner. Bigger amplitudes of motion resulted in a higher degree of dose blurring. Severe underdosages were observed when deliberately selecting the PTV wrongly, their extent being correlated with the degree of margin error. IMRT motionaveraged dose distributions exhibited areas of high dose in the gross tumour volume (GTV) which were not present in the static irradiations, arising from booster segments that the optimizer was creating to achieve planning target volume (PTV) homogeneity during the inverse-planning process. 3DCRT, on the other hand, did not demonstrate such effects. It has been concluded that care should be taken to control the delivered fluence when delivering IMRT to the breathing lung, even when the PTV margin has been adequately chosen to include the extent of the breathing motion.