Fuss M, Wenz F, Scholdei R, Essig M, Debus J, Knopp M V, Wannenmacher M
Department of Radiation Oncology, University of Heidelberg, Heidelberg, Germany.
Int J Radiat Oncol Biol Phys. 2000 Aug 1;48(1):53-8. doi: 10.1016/s0360-3016(00)00590-3.
New tumor-conformal radiation-treatment modalities have been established with the intention to spare normal tissue while maintaining or improving local tumor control. To document radiation-induced changes in normal brain and low-grade astrocytoma we measured regional cerebral blood volumes (rCBV) using a dynamic susceptibility-weighted contrast-enhanced MR technique (DSC-MRI). We attempted to assess pretherapeutic rCBV values and time- and dose-dependent changes following radiotherapy.
For prospective and longitudinal assessment of rCBV in normal brain and low-grade astrocytoma, 25 patients with histologically proven fibrillary astrocytoma (WHO Grade II) were examined before radiotherapy and during follow-up. Based on CT- and MR-data sets in a stereotactic setup, three-dimensional (3D) treatment planning was done. Radiotherapy was delivered using fractionated stereotactic radiotherapy (FSRT) to mean and median total doses of 60.9 and 60 Gy, respectively (range, 55.8-66 Gy). During MR imaging for treatment planning and follow-up examinations, 55 T2-weighted gradient echo images were acquired before, during, and after intravenous contrast bolus injection. The acquired signal-time curves were converted into concentration-time curves. The area under the tissue concentration-time curve was calculated and normalized to an integrated arterial input function. Thus, absolute rCBV values could be calculated.
Pretherapeutic mean rCBV for normal gray (GM) and white brain matter (WM) were 7.2 +/- 2.7 and 3.6 +/- 1.5 mL/100 g tissue, respectively. Mean rCBV for astrocytoma was 6.5 +/- 3.7 mL/100 g tissue. After radiotherapy, rCBV for GM and WM was significantly reduced (p < 0.01) in high-dose areas (40-100% of total dose). A nonsignificant reduction was measured in low-dose areas (up to 40% of total dose). Reduction of rCBV in astrocytomas to a plateau level of 4.6 +/- 0.4 mL/100 g tissue was measured at 6 months after radiotherapy and remained stable in locally controlled tumors.
Monitoring of rCBV changes in normal brain and low-grade astrocytoma was feasible using a DSC-MRI technique. The method was able to document radiation effects in low-grade astrocytoma, even if the majority of tumors showed no change in diagnostic MR-imaging. Radiation induced decrease of rCBV in GM and WM was correlated to total dose delivered to a tissue area, with high doses causing a significant decrease. Minor decline of rCBV in GM and WM outside high-dose areas after stereotactic radiotherapy confirms the efficacy to spare normal brain tissue by the use of modern conformal radiotherapy techniques. Nonetheless, a critical minimal dose initiating rCBV changes is yet unknown.
已建立新的肿瘤适形放射治疗模式，旨在在维持或改善局部肿瘤控制的同时保护正常组织。为记录正常脑和低级别星形细胞瘤的放射诱导变化，我们使用动态磁敏感加权对比增强磁共振技术（DSC-MRI）测量局部脑血容量（rCBV）。我们试图评估治疗前rCBV值以及放疗后的时间和剂量依赖性变化。
为对正常脑和低级别星形细胞瘤的rCBV进行前瞻性和纵向评估，对25例经组织学证实为纤维型星形细胞瘤（WHO二级）的患者在放疗前及随访期间进行检查。基于立体定向设置中的CT和MR数据集进行三维（3D）治疗计划。采用分次立体定向放射治疗（FSRT）进行放疗，平均和中位总剂量分别为60.9和60 Gy（范围55.8 - 66 Gy）。在用于治疗计划和随访检查的MR成像过程中，在静脉注射对比剂团注前、期间和之后采集55幅T2加权梯度回波图像。将采集到的信号-时间曲线转换为浓度-时间曲线。计算组织浓度-时间曲线下的面积并根据综合动脉输入函数进行归一化。因此，可以计算出绝对rCBV值。
正常灰质（GM）和白质（WM）的治疗前平均rCBV分别为7.2±2.7和3.6±1.5 mL/100 g组织。星形细胞瘤的平均rCBV为6.5±3.7 mL/100 g组织。放疗后，高剂量区域（总剂量的40 - 100%）的GM和WM的rCBV显著降低（p < 0.01）。低剂量区域（总剂量的40%以下）测量到的降低不显著。放疗后6个月测量到星形细胞瘤的rCBV降低至稳定水平4.6±0.4 mL/100 g组织，并且在局部控制的肿瘤中保持稳定。
使用DSC-MRI技术监测正常脑和低级别星形细胞瘤的rCBV变化是可行的。该方法能够记录低级别星形细胞瘤的放射效应，即使大多数肿瘤在诊断性MR成像中没有变化。GM和WM中放射诱导的rCBV降低与传递到组织区域的总剂量相关，高剂量导致显著降低。立体定向放疗后高剂量区域以外的GM和WM的rCBV轻微下降证实了使用现代适形放疗技术保护正常脑组织的有效性。尽管如此，引发rCBV变化的临界最小剂量仍未知。
