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Monaco是瑞典医科达公司研发的一款用于外照射的治疗计划系统(treatment planning system,TPS)。有别于其他主流TPS,Monaco采用简化的蒙特卡罗算法进行剂量计算[1-2],与其他TPS相比,Monaco的精确度较高[3-4]。在5.0版本的Monaco推出后,优化算法有了显著改善,配合生物优化函数的使用,使得Monaco成为了一套出色的TPS[5-7]。
采用容积旋转调强治疗(volume-modulated arc therapy,VMAT)计划进行逆向优化时,通量转化为可执行子野序列的算法是TPS较为核心的技术。Monaco采用扫地序列式的子野进行剂量投递,即在每个等间距的特定机架角度内,光栅从照射范围的一侧移动至另一侧。Monaco的优点:每个控制点处光栅形成的子野在x轴方向上的平均宽度较大,窄条状射野相对少;各控制点间的光栅变化较规律。这些优点有助于改善剂量验证结果,但是,同时也会限制整个计划的剂量调制能力。为此,Monaco采用了有别于其他TPS的1野多弧设计来提高剂量调制能力,1个射野最多可以添加4个弧。当计划使用1野2弧进行设计时,在优化进程的第2步,TPS会把第1步优化得到的通量沿着x轴方向拆分为左右2个部分,第1个弧照射左半边,第2个弧照射右半边。这样,在增加剂量调制度的同时,又因每个控制点处光栅最大运动范围变小,导致每个弧的照射时间减少。当横断面上靶区可以被拆分为相互孤立的两部分时,1野2弧可以得到很好地应用,如对于鼻咽癌患者,一般在计划设计时均采用1野2弧,与1野1弧或2野1弧相比,在照射颈部靶区时其更容易保护两部分靶区之间的器官和组织。目前,1野2弧的通量拆分方式是非常明确的,其是沿着x轴将通量分为2份,但对于1野3弧和1野4弧的通量拆分方式,在厂家能够提供的技术资料及以往的文献报道中均未见。因此,我们通过研究探求Monaco中1野3孤和1野4弧的通量拆分方式,为物理师使用Monaco进行计划设计及多弧选取时提供理论参考。
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拥有2、3、4个孤立靶区的模拟患者分别使用1野2、3、4弧进行优化后,得到各弧在机架角度最接近0°的控制点处的射野形状(图2)。使用1野多弧照射多个孤立靶区时,各弧按照先后顺序,在射野方向观(beam's eye view,BEV)上由左至右照射了各个靶区。特别是在采用1野2、3、4弧分别同时照射2、3、4个孤立靶区时,各弧按照先后顺序,从左至右分别照射了不同的靶区,如图2A中的a2、b2,图2B中的a3、b3 、c3,图2C中的a4、b4、c4、d4。
图 2 3例模拟患者容积旋转调强治疗计划中机架最接近0°时射野方向观上的射野形状
Figure 2. The shape of the radiation field in the beam's eye view direction when the gantry angle of each arc was closest to 0° in the volume-modulated arc therapy of three simulated patients
采用1野多弧同时照射2、3、4个孤立靶区时,各弧主要照射的靶区位置情况见表1。1野3弧和1野4弧照射多个靶区时,各弧是按照先后顺序,在BEV上由左至右照射了各个靶区。由此可知,Monaco计划系统采用1野多弧设置时,通量的拆分方式与1野2弧类似,都是沿着x轴方向进行分割,计划设置了几个弧,通量就会沿着x轴拆分成几份;且各弧是按照先后顺序,在BEV上由左至右进行照射。
计划 2 个靶区 3 个靶区 4 个靶区 1 区 2 区 1 区 2 区 3 区 1 区 2 区 3 区 4 区 1 野 2 弧 第 1 弧 √ − √ √ − √ √ − − 第 2 弧 − √ − √ √ − − √ √ 1 野 3 弧 第 1 弧 √ − √ − − √ − − − 第 2 弧 √ √ − √ − − √ √ − 第 3 弧 − √ − − √ − − − √ 1 野 4 弧 第 1 弧 √ − √ − − √ − − − 第 2 弧 √ − √ √ − − √ − − 第 3 弧 − √ − √ √ − − √ − 第 4 弧 − √ − − √ − − − √ 注:√ 表示该靶区被相应的弧主要照射;−表示该靶区射野较少或者未被照射到。1~4 区分别为模拟患者照射靶区由左至右的编号 表 1 模拟患者容积旋转调强治疗中采用1野2、3、4弧照射2、3、4个孤立靶区时各弧主要照射的靶区位置
Table 1. The main irradiating positions of each arc when 2, 3 and 4 carcs of 1 beam were used to irradiate 2, 3 and 4 isolated targets in the simulated patients by volume-modulated arc therapy
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全脑预防性照射、鼻咽癌和宫颈癌患者使用Matrixx剂量验证系统进行剂量测量获得的计划剂量分布及计划中各弧的剂量分布见图3。在9个计划中,通过每个计划的剂量分布与其每个弧的剂量分布间的位置比较,可以清晰地可见Monaco计划系统采用1野多弧设置时的通量拆分方式,即通量是沿着x轴方向进行分割的,计划设置了几个弧,通量就会沿着x轴拆分成几份,且每个弧是按照先后顺序,在BEV上由左至右进行照射。
Monaco计划系统一野多弧的通量拆分方式研究
Study on fluence splitting of single-beam multi-arc in Monaco planning system
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摘要:
目的 研究Monaco计划系统采用1野多弧设置时,通量的具体拆分方式。 方法 (1)模拟计划:选用密度均匀的圆柱形Delta4模体,在模体的CT图像上分别勾画2、3、4个横向整齐排列的圆柱形结构,模拟3例分别采用1野多弧照射2、3、4个孤立靶区的肿瘤患者,观察每个射野形状与靶区的位置关系,分析其规律性。(2)患者投照:采用完全随机法选取吉林省肿瘤医院经过放射治疗的3例患者,包括全脑预防性照射、鼻咽癌、宫颈癌患者,对每例患者分别设计3个容积旋转调强治疗计划,均为一个360°的射野,分别采用1野2、3、4弧进行治疗。所有计划的机架角度均归0°后,在加速器上执行计划,并使用Matrixx剂量验证系统分别测量每个计划的总剂量和每个弧的剂量,比较每个计划的总剂量与其每个弧剂量间的位置关系。 结果 模拟计划和患者投照研究结果均显示,在射野方向观(BEV)上,通量沿着x轴进行分割,通量分割的份数与计划中弧的数量相等;且各弧是按照先后顺序,在BEV上由左至右进行照射。 结论 了解Monaco计划系统的通量拆分方式,可为其在临床中的实际应用提供指导。 -
关键词:
- 放射疗法 /
- Monaco计划系统 /
- 容积旋转调强治疗 /
- 一野多弧 /
- 通量拆分
Abstract:Objective To study the specific splitting mode of fluence in Monaco planning system with single-beam multi-arc. Methods (1) Simulation plan: two, three, and four cylindrical structures were drawn along the x direction on the CT image of the cylindrical Delta4 phantom with uniform density to simulate three cases that need to irradiate two, three, and four isolated target volumes at the same time, respectively, to observe the relationship between the shape of the irradiation fields and the target volumes and analyze their regularity. (2) Patient irradiation: the following past cases in Jilin Cancer Hospital were completely random selected: one case of whole brain prophylactic irradiation, one case of nasopharyngeal carcinoma, and one case of cervical cancer. Three volume-modulated arc therapy plans were designed for each patient. A 360° beam was used in all plans, and the difference is that the numbers of arcs were two, three, and four, respectively. The gantry angles of all real case plans were set to 0°, the real patient plans were delivered on the accelerator, and the Matrixx dose verification system was used to measure the total dose of the plans and the partial dose per arc. Compare the positional relationship between the total dose for each plan and its dose per arc. Results The results of simulation plan and patient irradiation study showed that on the beam's eye view (BEV), the fluence was divided along the x-axis, and the number of fluence divisions was equal to the number of arcs in the plan. Each arc was illuminated from left to right in the BEV direction in sequence. Conclusion The fluence splitting mode in Monaco planning system was elucidated, providing guidance for its practical application in clinic. -
表 1 模拟患者容积旋转调强治疗中采用1野2、3、4弧照射2、3、4个孤立靶区时各弧主要照射的靶区位置
Table 1. The main irradiating positions of each arc when 2, 3 and 4 carcs of 1 beam were used to irradiate 2, 3 and 4 isolated targets in the simulated patients by volume-modulated arc therapy
计划 2 个靶区 3 个靶区 4 个靶区 1 区 2 区 1 区 2 区 3 区 1 区 2 区 3 区 4 区 1 野 2 弧 第 1 弧 √ − √ √ − √ √ − − 第 2 弧 − √ − √ √ − − √ √ 1 野 3 弧 第 1 弧 √ − √ − − √ − − − 第 2 弧 √ √ − √ − − √ √ − 第 3 弧 − √ − − √ − − − √ 1 野 4 弧 第 1 弧 √ − √ − − √ − − − 第 2 弧 √ − √ √ − − √ − − 第 3 弧 − √ − √ √ − − √ − 第 4 弧 − √ − − √ − − − √ 注:√ 表示该靶区被相应的弧主要照射;−表示该靶区射野较少或者未被照射到。1~4 区分别为模拟患者照射靶区由左至右的编号 -
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