Field size reduction enables ISO-NTCP escalation of tumor control probability for irradiation of lung tumors
Field size reduction enables ISO-NTCP escalation of tumor control probability for irradiation of lung tumors
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DOI：
10.1016/s0360-3016(01)01729-1
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发表时间：
2001-12-01
影响因子：
7
通讯作者：
Damen, EMF
中科院分区：
文献类型：
--
作者：
Engelsman, M;Remeijer, P;Damen, EMF
目的：用平均肺剂量（MLD）作为肺的正常组织并发症概率（NTCP）的估计值，我们评估了肺肿瘤的肿瘤控制概率是否可以通过剂量递增结合射野大小的减小来增加，从而增加靶剂量不均匀性，同时保持恒定的MLD。方法和材料：使用数值模拟对位于圆柱对称肺等效体模中的肺肿瘤的8 MV AP-PA照射进行建模。模拟了由于患者呼吸和设置错误引起的临床靶体积（CTV）的移动。肿瘤控制的概率，表示为CTV的等效均匀剂量（EUD），在恒定MLD的约束下，作为射野大小的函数进行评估。使用临床应用的治疗计划的射束方向对非小细胞肺癌（NSCLC）患者的治疗测试了该方法。在体模模拟中，通过选择确保CTV中95%的最小剂量的射野大小，（“常规”计划）考虑到设置误差和肿瘤运动，对于44.2戈伊的处方剂量，可以获得43.8戈伊的CTV的EUD。通过减小射野尺寸并因此向内移动95%等剂量表面，EUD增加到最大值68.3戈伊，CTV中的最小剂量为55.2戈伊。EUD的增加是由于射野尺寸减小使得处方剂量增加，同时保持恒定的MLD。射野尺寸的进一步减小导致EUD的减小，因为CTV中的最小剂量变得如此之低，以至于尽管处方剂量进一步增加，但其对EUD具有主要影响。对于NSCLC患者，EUD可以从常规计划的初始62.2戈伊增加到最大83.2戈伊。在该最大值中，处方剂量为88.1戈伊，CTV中的最小剂量为67.4戈伊。在这种情况下，95%的等剂量表面是符合密切的“静态”CTVduring treatment planning.Conclusions：异NTCP升级的肿瘤控制的概率是可能的肺肿瘤，通过减少字段大小，并允许更大的剂量不均匀性的CTV。在肺NTCP恒定的条件下，可以导出CTV中具有最高EUD和最高最小剂量的最佳射野尺寸。我们的结论是，在目标体积的均匀剂量的概念是不是最好的方法，以达到最高的概率肿瘤控制肺肿瘤。(C)2001 Elsevier Science Inc.
Purpose: With the mean lung dose (MLD) as an estimator for the normal tissue complication probability (NTCP) of the lung, we assessed whether the probability of tumor control of lung tumors might be increased by dose escalation in combination with a reduction of field sizes, thus increasing target dose inhomogeneity while maintaining a constant MLD.Methods and Materials: An 8-MV AP-PA irradiation of a lung tumor, located in a cylindrically symmetric lung-equivalent phantom, was modeled using numerical simulation. Movement of the clinical target volume (CTV) due to patient breathing and setup errors was simulated. The probability of tumor control, expressed as the equivalent uniform dose (EUD) of the CTV, was assessed as a function of field size, under the constraint of a constant MLD. The approach was tested for a treatment of a non-small cell lung cancer (NSCLC) patient using the beam directions of the clinically applied treatment plan.Results: In the phantom simulation it was shown that by choosing field sizes that ensured a minimum dose of 95% in the CTV ("conventional" plan) taking into account setup errors and tumor motion, an EUD of the CTV of 43.8 Gy can be obtained for a prescribed dose of 44.2 Gy. By reducing the field size and thus shifting the 95% isodose surface inwards, the EUD increases to a maximum of 68.3 Gy with a minimum dose in the CTV of 55.2 Gy. This increase in EUD is caused by the fact that field size reduction enables escalation of the prescribed dose while maintaining a constant MLD. Further reduction of the field size results in decrease of the EUD because the minimum dose in the CTV becomes so low that it has a predominant effect on the EUD, despite further escalation of the prescribed dose. For the NSCLC patient, the EUD could be increased from an initial 62.2 Gy for the conventional plan, to 83.2 Gy at maximum. In this maximum, the prescribed dose is 88.1 Gy, and the minimum dose in the CTV is 67.4 Gy. In this case, the 95% isodose surface is conformed closely to the "static" CTV during treatment planning.Conclusions: Iso-NTCP escalation of the probability of tumor control is possible for lung tumors by reducing field sizes and allowing a larger dose inhomogeneity in the CTV. Optimum field sizes can be derived, having the highest EUD and highest minimum dose in the CTV under condition of a constant NTCP of the lungs. We conclude that the concept of homogeneous dose in the target volume is not the best approach to reach the highest probability of tumor control for lung tumors. (C) 2001 Elsevier Science Inc.