WE-G-BRCD-05：使用容积调强弧形治疗（VMAT）评估适形调强放射治疗（CSA）投送的定位误差

WE-G-BRCD-05: Evaluation of Localization Errors for CSA Delivery Using VMAT.

作者信息

Myers P, Stathakis S, Esquivel C, Gutierrez A, Mavroidis P, Papanikolaou N

机构信息

Cancer Therapy and Research Center at UT Health Science Center, San Antonio, TX.

Karolinska Institutet & Stockholm University, Stockholm, Sweden.

出版信息

Med Phys. 2012 Jun;39(6Part28):3965. doi: 10.1118/1.4736182.

DOI:10.1118/1.4736182

PMID:28519609

Abstract

PURPOSE

To dosimetrically evaluate the effects of improper patient positioning in the junction area of a VMAT cranio-spinal axis irradiation technique consisting of one superior and one inferior arc.

METHODS

Five (n=5) cranio-spinal axis irradiation patients were planned with 2 arcs: one superior and one inferior. The plans were then recalculated with inferior isocenter shifted, in order to mimic patient setup errors, eight times: lmm, 2mm, 5mm, and 10mm superiorly, and 1mm, 2mm, 5mm, and 10mm inferiorly. Plans were then compared to the original, non-shifted arc plan based on target metrics of conformity number and homogeneity index, as well as several normal structure mean doses.

RESULTS

Percent differences were calculated in order to compare each of the eight shifted plans to the original arc plan without shifts, which would be the ideal setup of patient without error. The conformity number was on average 0.87%, 2.74%, 5.75%, and 9.10% lower for the 1mm, 2mm, 5mm, and 10mm inferiorly- shifted plans and 0.41%, 0.82%, 2.75%, and 5.99% lower for the respective superiorly-shifted plans. The homogeneity indices were, averaged among the five patients, 0.03%, 0.26%, 0.97%, and 2.84% for the inferior shifts and 0.23%, 1.17%, 6.31%, and 15.29% worse, or less homogenous for the superior shifts. Overall the mean doses to the organs at risk were less than 2% different for the 1mm, 2mm, and 5mm shifted plans. The 10mm shifted plans, however, showed percent differences from original plan of up to 5.6% on average.

CONCLUSIONS

Setup errors when shifting isocenters should be minimized in order to provide the patient with the best treatment possible. Errors of 1 to 2mm can negatively affect patient treatment, most notably in the arc junction area, but are not as problematic as larger errors of 5 to 10mm.

摘要

目的

通过剂量学方法评估在由一个上弧和一个下弧组成的容积调强弧形放疗（VMAT）颅脊髓轴照射技术的衔接区域中，患者体位不当所产生的影响。

方法

对5例颅脊髓轴照射患者进行了双弧计划设计，即一个上弧和一个下弧。然后将计划重新计算，使下等中心移位，以模拟患者摆位误差，移位情况为向上1mm、2mm、5mm和10mm，以及向下1mm、2mm、5mm和10mm，共8次。然后根据适形数和均匀性指数等靶区指标以及几个正常结构的平均剂量，将这些计划与原始的、未移位的弧形计划进行比较。

结果

计算百分比差异，以便将8个移位计划中的每一个与无移位的原始弧形计划进行比较，后者是理想的无误差患者摆位。对于向下移位1mm、2mm、5mm和10mm的计划，适形数平均分别比原始计划低0.87%、2.74%、5.75%和9.10%；对于相应的向上移位计划，适形数平均分别比原始计划低0.41%、0.82%、2.75%和5.99%。在5例患者中平均计算得出，向下移位时均匀性指数分别为0.03%、0.26%、0.97%和2.84%，向上移位时均匀性指数分别变差0.23%、1.17%、6.31%和15.29%，即均匀性更低。总体而言，对于移位1mm、2mm和5mm的计划，危及器官的平均剂量与原始计划的差异小于2%。然而，移位10mm的计划与原始计划相比，平均百分比差异高达5.6%。