The importance of tissue segmentation for dose calculations for kilovoltage radiation therapy
The importance of tissue segmentation for dose calculations for kilovoltage radiation therapy
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DOI：
10.1118/1.3589138
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发表时间：
2011-06-01
期刊：
影响因子：
3.8
通讯作者：
Graves, Edward E.
中科院分区：
文献类型：
--
作者：
Bazalova, Magdalena;Graves, Edward E.
目的：这项工作的目的是评估组织分割对千伏放射治疗的蒙特卡罗（MC）剂量计算准确性的影响，这是临床前放射治疗研究中常用的，也正在重新审视作为一种临床治疗方式。常规的组织质量密度的差异的基础上进行的组织分割的可行性进行了研究和一个新的分割方案的基础上的差异，有效atomic numbers.Methods：MC剂量计算在一个圆柱形的小鼠体模与小圆柱形的不均匀性组成的34 ICRU-44组织进行使用EGSnrc/BEAMnrc和DOSXYZnrc代码。计算了目前用于小动物放射治疗的五种不同千伏束的组织剂量：microCT 120 kV束，两种用4 mm Al或0.5 mm Cu过滤的225 kV束，重度过滤的320 kV束和192 Ir束。研究了34个ICRU-44组织的平均剂量与组织质量密度、有效原子序数和射束能量的关系。为原位肺肿瘤模型创建治疗计划，并使用4、8和39个组织箱计算三种组织分割方案的剂量分布，以评估模拟结果对千伏放射治疗的意义。在我们的模型中，脂肪组织与肌肉的不正确分配导致剂量计算差异分别为27%，13%，120 kV和225 kV电子束分别用4 mm Al和0.5 mm Cu过滤后，其平均吸收率为7%。对于重度过滤的320 kV射束和192 Ir源，由于组织错误分配导致的潜在剂量计算差异低于4%。对于由等于或小于225 kV的管电位产生的X射线束，组织剂量与其质量密度之间没有明确的关系。二阶多项式拟合很好地近似了作为这些光束的有效原子序数的函数的组织吸收剂量。在小鼠研究中，与39组织分割方案相比，4和8组织分割方案对骨的120 kV射束剂量分别高估100%和低估10%。脂肪组织的剂量分别被高估30%和低估10%。在一般情况下，器官的危险（OAR）剂量高估4组织和8组织分割计划相比，39组织segmentation.Conclusions：组织分割被证明是一个关键参数的剂量计算与千伏束用于小动物放射治疗时，X射线管具有潜在的
Purpose: The aim of this work was to evaluate the effect of tissue segmentation on the accuracy of Monte Carlo (MC) dose calculations for kilovoltage radiation therapy, which are commonly used in preclinical radiotherapy studies and are also being revisited as a clinical treatment modality. The feasibility of tissue segmentation routinely done on the basis of differences in tissue mass densities was studied and a new segmentation scheme based on differences in effective atomic numbers was developed.Methods: MC dose calculations in a cylindrical mouse phantom with small cylindrical inhomogeneities consisting of 34 ICRU-44 tissues were performed using the EGSnrc/BEAMnrc and DOSXYZnrc codes. The dose to tissue was calculated for five different kilovoltage beams currently used in small animal radiotherapy: a microCT 120 kV beam, two 225 kV beams filtered with either 4 mm of Al or 0.5 mm of Cu, a heavily filtered 320 kV beam, and a 192Ir beam. The mean doses to the 34 ICRU-44 tissues as a function of tissue mass density and effective atomic number and beam energy were studied. A treatment plan for an orthotopic lung tumor model was created, and the dose distribution was calculated for three tissue segmentation schemes using 4, 8, and 39 tissue bins to assess the significance of the simulation results for kilovoltage radiotherapy.Results: In our model, incorrect assignment of adipose tissue to muscle caused dose calculation differences of 27%, 13%, and 7% for the 120 kV beam and the 225 kV beams filtered with 4 mm Al and 0.5 mm Cu, respectively. For the heavily filtered 320 kV beam and a 192Ir source, potential dose calculation differences due to tissue mis-assignment were below 4%. There was no clear relationship between the dose to tissue and its mass density for x-ray beams generated by tube potentials equal or less than 225 kV. A second order polynomial fit approximated well the absorbed dose to tissue as a function of effective atomic number for these beams. In the mouse study, the 120 kV beam dose to bone was overestimated by 100% and underestimated by 10% for the 4 and 8-tissue segmentation schemes compared to the 39-tissue segmentation scheme, respectively. Dose to adipose tissue was overestimated by 30% and underestimated by 10%, respectively. In general, organ at risk (OAR) doses were overestimated in the 4-tissue and the 8-tissue segmentation schemes compared to the 39-tissue segmentation.Conclusions: Tissue segmentation was shown to be a key parameter for dose calculations with kilovoltage beams used in small animal radiotherapy when an x-ray tube with a potential