Yeung Anamaria R, Vargas Carlos E, Falchook Aaron, Louis Debbie, Olivier Kenneth, Keole Sameer, Yeung Daniel, Mendenhall Nancy P, Li Zuofeng
Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA.
Int J Radiat Oncol Biol Phys. 2008 Dec 1;72(5):1426-33. doi: 10.1016/j.ijrobp.2008.03.031. Epub 2008 Aug 30.
To determine the influence of magnetic-resonance-imaging (MRI)-vs. computed-tomography (CT)-based prostate and normal structure delineation on the dose to the target and organs at risk during proton therapy.
Fourteen patients were simulated in the supine position using both CT and T2 MRI. The prostate, rectum, and bladder were delineated on both imaging modalities. The planning target volume (PTV) was generated from the delineated prostates with a 5-mm axial and 8-mm superior and inferior margin. Two plans were generated and analyzed for each patient: an MRI plan based on the MRI-delineated PTV, and a CT plan based on the CT-delineated PTV. Doses of 78 Gy equivalents (GE) were prescribed to the PTV.
Doses to normal structures were lower when MRI was used to delineate the rectum and bladder compared with CT: bladder V50 was 15.3% lower (p = 0.04), and rectum V50 was 23.9% lower (p = 0.003). Poor agreement on the definition of the prostate apex was seen between CT and MRI (p = 0.007). The CT-defined prostate apex was within 2 mm of the apex on MRI only 35.7% of the time. Coverage of the MRI-delineated PTV was significantly decreased with the CT-based plan: the minimum dose to the PTV was reduced by 43% (p < 0.001), and the PTV V99% was reduced by 11% (p < 0.001).
Using MRI to delineate the prostate results in more accurate target definition and a smaller target volume compared with CT, allowing for improved target coverage and decreased doses to critical normal structures.
确定基于磁共振成像（MRI）与基于计算机断层扫描（CT）的前列腺及正常结构勾画对质子治疗期间靶区和危及器官剂量的影响。
14例患者采用仰卧位，同时进行CT和T2 MRI模拟。在两种成像方式上均勾画前列腺、直肠和膀胱。根据勾画的前列腺生成计划靶区（PTV），轴向边缘为5 mm，上下边缘为8 mm。为每位患者生成并分析两个计划：基于MRI勾画的PTV的MRI计划和基于CT勾画的PTV的CT计划。向PTV处方78 Gy当量（GE）的剂量。
与CT相比，使用MRI勾画直肠和膀胱时，正常结构的剂量更低：膀胱V50降低15.3%（p = 0.04），直肠V50降低23.9%（p = 0.003）。CT和MRI在前列腺尖部定义上的一致性较差（p = 0.007）。CT定义的前列腺尖部仅在35.7%的时间内位于MRI上尖部的2 mm范围内。基于CT的计划显著降低了MRI勾画的PTV的覆盖范围：PTV的最小剂量降低了43%（p < 0.001），PTV V99%降低了11%（p < 0.001）。
与CT相比，使用MRI勾画前列腺可实现更准确的靶区定义和更小的靶区体积，从而改善靶区覆盖并降低关键正常结构的剂量。
