Prabhakar R, Rath G K
Department of Radiation Oncology, Institute Rotary Cancer Hospital, All India Institute of Medical Sciences, New Delhi, India.
Australas Phys Eng Sci Med. 2009 Dec;32(4):233-9. doi: 10.1007/BF03179244.
Dose volume histograms (DVHs) play a vital role in determining the optimal plan for radiotherapy treatment delivery. The current concepts of conformality index (CI), equivalent uniform dose (EUD) derived from dose volume histogram (DVH) does not provide any spatial information. In this study, slice-based evaluation methods have been proposed for spatially analyzing the radiotherapy treatment plans. A case of prostate cancer has been selected for demonstrating the proposed tools for evaluating the dose distribution. Three dimensional conformal radiotherapy treatment planning (3D-CRT) was performed to a dose of 27 Gy/15# with three fields (6 MV anteroposterior and two 15 MV lateral fields) employing multileaf collimator after delivering 45 Gy/25#. The dose was normalized to isocenter and the treatment plan was evaluated with DVH. The dose maximum point, conformality index, planning target volume coverage index (PCI), planning target volume overdose index (POI) and equivalent uniform dose (EUD) were evaluated for every single slice along the cranio-caudal direction for all the planning target volume (PTV) contours and plotted against the slice location. The dose maximum point plotted against the slice position helps in identifying the slices where the dose maximum point is outside the target volume. The plot of conformality index gives the information about the location of those slices where excess of surrounding normal tissues is encompassed inside the prescription isodose. POI quantifies the high dose regions inside the PTV slices that receive doses above 107% of the prescription dose. Similarly, the plot of PCI and EUD with slice position gives the information about those slices where the tumor is not covered adequately. The proposed methods in this study forms as a simpler way to assess the spatial distribution of the dose inside the target volume. It could be used in combination with the current plan evaluation tools and will be very helpful in analyzing the treatment plans.
剂量体积直方图（DVH）在确定放射治疗的最佳方案中起着至关重要的作用。当前基于剂量体积直方图（DVH）得出的适形指数（CI）、等效均匀剂量（EUD）的概念并未提供任何空间信息。在本研究中，已提出基于切片的评估方法用于对放射治疗方案进行空间分析。选取了一例前列腺癌病例来展示所提出的评估剂量分布的工具。在给予45 Gy/25次分割后，采用多叶准直器，通过三个射野（6 MV前后野和两个15 MV侧野）进行三维适形放射治疗计划（3D-CRT），剂量为27 Gy/15次分割。剂量归一化至等中心，并使用DVH对治疗计划进行评估。针对所有计划靶区（PTV）轮廓，沿头脚方向的每一个切片评估剂量最大值点、适形指数、计划靶区覆盖指数（PCI）、计划靶区超量指数（POI）和等效均匀剂量（EUD），并将其与切片位置进行绘图。剂量最大值点与切片位置的绘图有助于识别剂量最大值点位于靶区体积之外的切片。适形指数的绘图给出了那些在处方等剂量线内包含过多周围正常组织的切片位置信息。POI量化了PTV切片内接受高于处方剂量107%剂量的高剂量区域。同样，PCI和EUD与切片位置的绘图给出了肿瘤未得到充分覆盖的那些切片的信息。本研究中提出的方法形成了一种评估靶区内剂量空间分布的更简单方式。它可与当前的计划评估工具结合使用，对分析治疗计划非常有帮助。
