McLaughlin P W, Narayana V, Drake D G, Miller B M, Marsh L, Chan J, Gonda R, Winfield R J, Roberson P L
Department of Radiation Oncology, Providence Hospital, Southfield, MI, USA.
Int J Radiat Oncol Biol Phys. 2002 Nov 1;54(3):703-11. doi: 10.1016/s0360-3016(02)02991-7.
To determine the relative value of three MRI pulse sequences in defining the prostate volume after permanent implantation.
A total of 45 patients who received a permanent 125I implant were studied. Two weeks after implantation, an axial CT scan (2 mm thickness) and T1-weighted, T1-weighted fat saturation, and T2-weighted axial MRI (3-mm) studies were obtained. The prostate volumes were compared with the initial ultrasound planning volumes, and subsequently the CT, T1-weighted, and T1-weighted fat saturation MRI volumes were compared with the T2-weighted volumes. Discrepancies in volume were evaluated by visual inspection of the registered axial images and the registration of axial volumes on the sagittal T2-weighted volumes. In a limited set of patients, pre- and postimplant CT and T2-weighted MRI studies were available for comparison to determine whether prostate volume changes after implant were dependent on the imaging modality.
T1-weighted and T1-weighted fat saturation MRI and CT prostate volumes were consistently larger than the T2-weighted MRI prostate volumes, with a volume on average 1.33 (SD 0.24) times the T2-weighted volume. This discrepancy was due to the superiority of T2-weighted MRI for prostate definition at the following critical interfaces: membranous urethra, apex, and anterior base-bladder and posterior base-seminal vesicle interfaces. The differences in prostate definition in the anterior base region suggest that the commonly reported underdose may be due to overestimation of the prostate in this region by CT. The consistent difference in volumes suggests that the degree of swelling observed after implantation is in part a function of the imaging modality. In patients with pre- and postimplant CT and T2-weighted MRI images, swelling on the T2-weighted images was 1.1 times baseline and on CT was 1.3 times baseline, confirming the imaging modality dependence of prostate swelling.
Postimplant T2-weighted MRI images provided superior prostate definition in all critical regions of the prostate compared with CT and the other MRI sequences tested. In addition to defining an optimal technique, these findings call two prior observations into question. Under dosing at the anterior base region may be overestimated because of poor definition of the prostate-bladder muscle interface. The swelling observed after implantation was lower on T2-weighted images as well, suggesting that a fraction of postimplant swelling is a function of the imaging modality. These findings have implications for preimplant planning and postimplant evaluation. As implant planning techniques become more conformal, and registration methods become more efficient, T2-weighted MRI after implantation will improve the accuracy of postimplant dosimetry.
确定三种MRI脉冲序列在定义永久性植入后前列腺体积方面的相对价值。
共研究了45例接受永久性¹²⁵I植入的患者。植入后两周，进行了轴向CT扫描（层厚2mm）以及T1加权、T1加权脂肪饱和和T2加权轴向MRI（层厚3mm）检查。将前列腺体积与初始超声规划体积进行比较，随后将CT、T1加权和T1加权脂肪饱和MRI体积与T2加权体积进行比较。通过目视检查配准的轴向图像以及在矢状面T2加权体积上配准轴向体积来评估体积差异。在一组有限的患者中，可获得植入前后的CT和T2加权MRI研究结果以比较，从而确定植入后前列腺体积变化是否取决于成像方式。
T1加权和T1加权脂肪饱和MRI以及CT的前列腺体积始终大于T2加权MRI的前列腺体积，平均体积是T2加权体积的1.33（标准差0.24）倍。这种差异是由于T2加权MRI在以下关键界面定义前列腺方面具有优势：膜性尿道、尖部以及前基底部 - 膀胱和后基底部 - 精囊界面。前基底部区域前列腺定义的差异表明，通常报道的剂量不足可能是由于CT对该区域前列腺的高估。体积上的一致差异表明，植入后观察到的肿胀程度部分是成像方式的函数。在有植入前后CT和T2加权MRI图像的患者中，T2加权图像上的肿胀是基线的1.1倍，CT上是基线的1.3倍，证实了前列腺肿胀对成像方式的依赖性。
与CT及其他测试的MRI序列相比，植入后T2加权MRI图像在前列腺的所有关键区域提供了更好的前列腺定义。除了确定一种最佳技术外，这些发现还对之前的两项观察结果提出了质疑。由于前列腺 - 膀胱肌肉界面定义不佳，前基底部区域的剂量不足可能被高估。在T2加权图像上植入后观察到的肿胀也较低，这表明植入后肿胀的一部分是成像方式的函数。这些发现对植入前规划和植入后评估具有重要意义。随着植入规划技术变得更加适形，配准方法变得更加高效，植入后T2加权MRI将提高植入后剂量测定的准确性。
