Mayer R, Fong W, Frankel T, Simons S, Kleinberg L, Lee D J
Division of Radiation Oncology, Johns Hopkins Oncology Center, Johns Hopkins University, Baltimore, Maryland, USA.
Radiat Oncol Investig. 1998;6(1):35-51. doi: 10.1002/(SICI)1520-6823(1998)6:1<35::AID-ROI5>3.0.CO;2-J.
Radiation dose prescription, interpretation, and planning can be problematic for brachytherapy due to high spatial heterogeneity, varying and various dose rates, absence of superimposed calculated isodose distributions onto affected tissues, and lack of dose volume histograms. A new treatment planner has been developed to reduce these limitations in brachytherapy planning. The PC-based planning system uses a CT-simulator to sequentially scan the patient to generate orthogonal images (to localize seed positions) and subsequently axially scan the patient. This sequential scanning procedure avoids using multiple independent patient scans, templates, external frames, or fiducial markers to register the reconstructed seed positions with patient contours. Dose is computed after assigning activity to (low dose rate) Ir192, linear Cs137, or I125 seeds or dwell times (high dose rate) to the Ir192 source. The planar isodose distribution is superimposed onto axial, coronal, or sagittal views of the tissues following image reconstruction. The treatment plan computes (1) direct and cumulative volume dose histograms for individual tissues, (2) the average, standard deviation, and coefficient of skewness of the dose distribution within individual tissues, (3) an average (over all tissue pixels) survival probability (S) and average survival dose DASD for a given radiation treatment, (4) normal tissue complication probability (NTCP) delivered to a given tissue. All four computed quantities account for dose heterogeneity. These estimates of the biological response to radiation from laboratory-based studies may help guide the evaluation of the prescribed low- or high-dose rate therapy in retrospective and prospective clinical studies at a number of treatment sites.
由于高空间异质性、剂量率变化多样、缺乏叠加在受影响组织上的计算等剂量分布以及缺乏剂量体积直方图，近距离放射治疗的辐射剂量处方、解读和规划可能存在问题。已开发出一种新的治疗计划系统来减少近距离放射治疗规划中的这些限制。基于个人计算机的规划系统使用CT模拟器对患者进行序列扫描以生成正交图像（用于定位籽源位置），随后对患者进行轴向扫描。这种序列扫描程序避免了使用多个独立的患者扫描、模板、外部框架或基准标记来将重建的籽源位置与患者轮廓进行配准。在为（低剂量率）铱192、线性铯137或碘125籽源分配活度或为铱192源分配驻留时间（高剂量率）后计算剂量。在图像重建后，平面等剂量分布叠加在组织的轴向、冠状或矢状视图上。治疗计划计算：（1）各个组织的直接和累积体积剂量直方图；（2）各个组织内剂量分布的平均值、标准差和偏度系数；（3）给定放射治疗的平均（在所有组织像素上）生存概率（S）和平均生存剂量DASD；（4）给予特定组织的正常组织并发症概率（NTCP）。所有这四个计算量都考虑了剂量异质性。这些基于实验室研究的对辐射生物反应的估计可能有助于在多个治疗部位的回顾性和前瞻性临床研究中指导对规定的低剂量率或高剂量率治疗的评估。
