局部晚期宫颈癌图像引导自适应近距离治疗中 GEC ESTRO 靶区的表观扩散系数。
Apparent diffusion coefficients in GEC ESTRO target volumes for image guided adaptive brachytherapy of locally advanced cervical cancer.
机构信息
Department of Clinical Engineering, Aarhus University Hospital, Skejby, Aarhus, Denmark.
出版信息
Acta Oncol. 2010 Oct;49(7):978-83. doi: 10.3109/0284186X.2010.500619.
BACKGROUND AND PURPOSE
T2 weighted MRI is recommended for image guided adaptive brachytherapy (IGABT) in cervical cancer. Diffusion weighted imaging (DWI) and the derived apparent diffusion coefficient (ADC) may add additional biological information on tumour cell density. The purpose of this study was to evaluate the distribution of the ADC within target volumes as recommended by GEC-ESTRO: Gross Tumour Volume at BT (GTV(BT)), High-Risk Clinical Tumour Volume (HR-CTV) and Intermediate-Risk Clinical Target Volume (IR-CTV) and to evaluate the change of diffusion between fractions of IGABT.
MATERIAL AND METHODS
Fifteen patients with locally advanced cervical cancer were examined by MRI before their first (BT1) and second (BT2) fraction of IGABT, resulting in a total of 30 MR examinations including both T2 weighted and DWI sequences. The Apparent Diffusion Coefficient (ADC) was calculated by use of three levels of b-values (0, 600, 1000 s/mm(2)). ADC maps were constructed and fused with the GEC ESTRO target contours. The mean ADC value within each target volume was calculated. Furthermore, volumes of low diffusion (ADC(low)) were defined based on an ADC threshold of 1.2 × 10(-3) mm(2)/s, and overlap with target volumes was evaluated. Change of ADC level in target volumes and change of ADC(low) volume from BT1 to BT2 was also evaluated.
RESULTS
The mean ADC was significantly lower in GTV(BT) than in HR-CTV (p<0.001) which again was significantly lower than in IR-CTV (p<0.001). There was no significant change of the ADC(low) volume or ADC level within each target structure between BT1 and BT2 (p=0.242). All three GEC-ESTRO volumes contained volumes with low diffusion. The GTV(BT) contained 37.2% volume of low diffusion, HR-CTV 20.3% and IR-CTV 10.8%.
CONCLUSION
With DWI we were able to find a significant difference in ADC-values for the three different GEC ESTRO targets. This supports the assumption that the target volumes used for dose prescription in IGABT contain tissues with different characteristics, with the tumour (GTV(BT)) being the volume with the lowest diffusion. No significant changes were found from BT1 to BT2 indicating that changes of ADC level and volumes are stable at the time of BT. Further studies are needed to evaluate the role of DWI in target contouring and dose prescription for IGABT.
背景与目的
T2 加权 MRI 被推荐用于宫颈癌的图像引导自适应近距离放疗（IGABT）。扩散加权成像（DWI）及其衍生的表观扩散系数（ADC）可能会增加肿瘤细胞密度的额外生物学信息。本研究的目的是评估在 GEC-ESTRO 推荐的靶区（BT 时的大体肿瘤体积（GTV（BT））、高危临床肿瘤靶区（HR-CTV）和中危临床靶区（IR-CTV）内 ADC 的分布，并评估 IGABT 分次间扩散的变化。
材料与方法
15 例局部晚期宫颈癌患者在首次（BT1）和第二次（BT2）IGABT 分次前接受 MRI 检查，共进行了 30 次 MRI 检查，包括 T2 加权和 DWI 序列。使用三个 b 值（0、600、1000 s/mm2）计算表观扩散系数（ADC）。构建 ADC 图并与 GEC ESTRO 靶区轮廓融合。计算每个靶区的平均 ADC 值。此外，基于 1.2×10-3mm2/s 的 ADC 阈值定义低扩散（ADC(low))体积，并评估与靶区的重叠。评估靶区 ADC 水平的变化和 BT1 至 BT2 时 ADC(low)体积的变化。
结果
GTV（BT）的平均 ADC 明显低于 HR-CTV（p<0.001），而 HR-CTV 又明显低于 IR-CTV（p<0.001）。在 BT1 和 BT2 之间，每个靶区结构的 ADC(low)体积或 ADC 水平均无显著变化（p=0.242）。GEC-ESTRO 的所有三个体积均包含低扩散体积。GTV（BT）包含 37.2%的低扩散体积，HR-CTV 为 20.3%，IR-CTV 为 10.8%。
结论
通过 DWI，我们能够发现 GEC ESTRO 三个不同靶区的 ADC 值存在显著差异。这支持了靶区用于 IGABT 剂量规定的假设，即靶区包含具有不同特征的组织，肿瘤（GTV（BT））是扩散最低的体积。从 BT1 到 BT2 没有发现明显的变化，这表明 ADC 水平和体积的变化在 BT 时是稳定的。需要进一步的研究来评估 DWI 在 IGABT 靶区勾画和剂量规定中的作用。
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