Integral dose investigation of non-coplanar treatment beam geometries in radiotherapy
Integral dose investigation of non-coplanar treatment beam geometries in radiotherapy
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DOI：
10.1118/1.4845055
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发表时间：
2014-01-01
期刊：
影响因子：
3.8
通讯作者：
Sheng, Ke
中科院分区：
文献类型：
--
作者：
Dan Nguyen;Dong, Peng;Sheng, Ke
目的：已经开发出涉及大量射野的非共面计划（例如 4 pi 放射治疗）的自动规划和交付，以利用 C 臂龙门直线加速器上新推出的自动化床和龙门。然而，人们越来越担心需要研究的积分剂量的潜在变化。 方法：本研究纳入了数字躯干模型和 22 名肺和肝立体定向放射治疗 (SBRT) 患者。数字体模被构造为水当量椭圆柱，长轴长度为 35.4 厘米，短轴长度为 23.6 厘米。直径为 4.5 厘米的目标沿主轴线放置在不同的深度。将形成圆锥形图案的强度调制非共面光束的积分剂量与等距共面光束计划进行比较。还对模型几何形状和光束数量的积分剂量依赖性进行了量化。对于患者计划，使用列生成和定价方法优化非共面和共面光束和注量，并与使用从肿瘤近侧进入的两个完整（肺）或部分共面弧（肝脏）的临床 VMAT 计划进行比较。评估和比较正常组织体积的平均剂量和接受大于 2 Gy (V2) 和 5 Gy (V5) 的总体积。 结果：非共面和共面计划的积分剂量比取决于体模的肿瘤深度；对于浅于10cm的肿瘤，非共面积分剂量低于非共面角度小于60度的共面积分剂量。在患者计划中也观察到类似的模式。对于 6-8 厘米深的肿瘤，观察到最小的非共面积分剂量。对于体模，积分剂量与射束数量无关，与肝脏 SBRT 患者一致，但肺 SBRT 患者在使用更多射束时表现出积分剂量略有增加。较大的肿瘤尺寸和较大的患者体型并没有改变非共面和共面病例之间的整体剂量关系。然而，薄盘形肿瘤在非共面计划中接受的整体剂量至少高出 40%。总体而言，患者非共面积分剂量和 V5 与来自相同优化引擎的共面剂量相当，并且比最先进的 VMAT 计划低 15%-20%。然而，非共面光束显着增加了模型和患者的 V2。平均而言，接受剂量大于 2 Gy 的肺和肝脏 SBRT 患者正常组织体积分别增加了 749 和 532 cm(3)。结论：作者使用模拟患者躯干的数字体模和 22 名 SBRT 患者来表明，采用优化非共面光束的计划的积分剂量与使用相同数量离散光束的共面计划的积分剂量相当，并且显着低于 VMAT 的积分剂量计划。非共面光束将较大的正常组织体积暴露于非零剂量，需要单独评估其影响以确定非共面计划的风险/效益比。 (C) 2014 年美国医学物理学家协会。
Purpose: Automated planning and delivery of non-coplanar plans such as 4 pi radiotherapy involving a large number of fields have been developed to take advantage of the newly available automated couch and gantry on C-arm gantry linacs. However, there is an increasing concern regarding the potential changes in the integral dose that needs to be investigated.Methods: A digital torso phantom and 22 lung and liver stereotactic body radiation therapy (SBRT) patients were included in the study. The digital phantom was constructed as a water equivalent elliptical cylinder with a major axis length of 35.4 cm and minor axis of 23.6 cm. A 4.5 cm diameter target was positioned at varying depths along the major axis. Integral doses from intensity modulated, non-coplanar beams forming a conical pattern were compared against the equally spaced coplanar beam plans. Integral dose dependence on the phantom geometry and the beam number was also quantified. For the patient plans, the non-coplanar and coplanar beams and fluences were optimized using a column generation and pricing approach and compared against clinical VMAT plans using two full (lung) or partial coplanar arcs (liver) entering at the side proximal to the tumor. Both the average dose to the normal tissue volume and the total volumes receiving greater than 2 Gy (V2) and 5 Gy (V5) were evaluated and compared.Results: The ratio of integral dose from the non-coplanar and coplanar plans depended on the tumor depth for the phantom; for tumors shallower than 10 cm, the non-coplanar integral doses were lower than coplanar integral doses for non-coplanar angles less than 60 degrees. Similar patterns were observed in the patient plans. The smallest non-coplanar integral doses were observed for tumor 6-8 cm deep. For the phantom, the integral dose was independent of the number of beams, consistent with the liver SBRT patients but the lung SBRT patients showed slight increase in the integral dose when more beams were used. Larger tumor size and larger patient body size did not change the overall relationship of integral doses between non-coplanar and coplanar cases. However, the thin disk-shaped tumor received at least 40% greater integral doses with the non-coplanar plans. Overall, patient non-coplanar integral doses and V5 were comparable to those of coplanar doses from the same optimization engine and 15%-20% lower than state of the art VMAT plans. However, non-coplanar beams significantly increased V2 in both the phantom and patients. On average, the lung and liver SBRT patient normal tissue volumes receiving dose greater than 2 Gy were increased by 749 and 532 cm(3), respectively.Conclusions: The authors used a digital phantom simulating a patient torso and 22 SBRT patients to show that the integral doses from the plans employing optimized non-coplanar beams are comparable to those of the coplanar plans using an equal number of discrete beams and are significantly lower than those of VMAT plans. The non-coplanar beams expose a larger normal tissue volume to non-zero doses, whose impact will need to be evaluated individually to determine the risk/benefit ratio of the non-coplanar plans. (C) 2014 American Association of Physicists in Medicine.