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首页> 美国卫生研究院文献>Technology in Cancer Research Treatment >MRI-Related Geometric Distortions in Stereotactic Radiotherapy Treatment Planning: Evaluation and Dosimetric Impact
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MRI-Related Geometric Distortions in Stereotactic Radiotherapy Treatment Planning: Evaluation and Dosimetric Impact

机译：立体定向放射治疗规划中与MRI相关的几何变形：评估和剂量学影响

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In view of their superior soft tissue contrast compared to computed tomography, magnetic resonance images are commonly involved in stereotactic radiosurgery/radiotherapy applications for target delineation purposes. It is known, however, that magnetic resonance images are geometrically distorted, thus deteriorating dose delivery accuracy. The present work focuses on the assessment of geometric distortion inherent in magnetic resonance images used in stereotactic radiosurgery/radiotherapy treatment planning and attempts to quantitively evaluate the consequent impact on dose delivery. The geometric distortions for 3 clinical magnetic resonance protocols (at both 1.5 and 3.0 T) used for stereotactic radiosurgery/radiotherapy treatment planning were evaluated using a recently proposed phantom and methodology. Areas of increased distortion were identified at the edges of the imaged volume which was comparable to a brain scan. Although mean absolute distortion did not exceed 0.5 mm on any spatial axis, maximum detected control point disposition reached 2 mm. In an effort to establish what could be considered as acceptable geometric uncertainty, highly conformal plans were utilized to irradiate targets of different diameters (5-50 mm). The targets were mispositioned by 0.5 up to 3 mm, and dose–volume histograms and plan quality indices clinically used for plan evaluation and acceptance were derived and used to investigate the effect of geometrical uncertainty (distortion) on dose delivery accuracy and plan quality. The latter was found to be strongly dependent on target size. For targets less than 20 mm in diameter, a spatial disposition of the order of 1 mm could significantly affect (>5%) plan acceptance/quality indices. For targets with diameter greater than 2 cm, the corresponding disposition was found greater than 1.5 mm. Overall results of this work suggest that efficacy of stereotactic radiosurgery/radiotherapy applications could be compromised in case of very small targets lying distant from the scanner’s isocenter (eg, the periphery of the brain).
机译：鉴于与计算机断层扫描相比，它们的优越的软组织对比度，磁共振成像通常在立体定向放射外科/放射治疗应用中涉及以达到目标描绘的目的。然而，众所周知，磁共振图像在几何上是失真的，因此降低了剂量输送的准确性。目前的工作集中在对立体定向放射外科/放射治疗治疗计划中使用的磁共振图像中固有的几何变形的评估，并试图定量评估其对剂量输送的影响。使用最近提出的幻象和方法，对用于立体定向放射外科/放射疗法治疗计划的3种临床磁共振方案（在1.5和3.0 T时）的几何变形进行了评估。在成像体积的边缘识别出失真增加的区域，这与脑部扫描相当。尽管在任何空间轴上平均绝对变形不超过0.5 mm，但最大检测到的控制点位置仍达到2 mm。为了确定可以接受的几何不确定度，采用了高度保形的计划来照射不同直径（5-50毫米）的目标。将目标位置错位0.5mm至3mm，并得出临床上用于计划评估和接受的剂量-体积直方图和计划质量指数，并用于研究几何不确定性（失真）对剂量输送准确性和计划质量的影响。发现后者在很大程度上取决于目标大小。对于直径小于20毫米的目标，大约1毫米的空间位置可能会显着影响（> 5％）计划验收/质量指标。对于直径大于2厘米的目标，发现相应的布置大于1.5毫米。这项工作的总体结果表明，如果很小的目标远离扫描仪的等角点（例如，大脑的外围），则可能会损害立体定向放射外科手术/放射治疗应用的功效。

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