Zwicker R D, Schmidt-Ullrich R
Radiation Oncology Department, Medical College of Virginia, Richmond 23298-0058.
Int J Radiat Oncol Biol Phys. 1995 Jan 1;31(1):149-55. doi: 10.1016/0360-3016(94)00346-M.
This work makes use of a volume-ratio technique to examine dose uniformity in a planar interstitial implant system based entirely on geometrical constraints. The rationale for determining an upper limit for acceptable dose variation is examined and discussed. Variation of ribbon spacing and interplanar separation is evaluated in terms of its effect on dose homogeneity.
Volume-dose curves were generated for a range of planar implant dimensions. The volume inside the target region and enclosed between the reference isodose and a higher isodose surface was calculated as a measure of dose uniformity. Studies of homogeneity, target coverage, and external tissue irradiation were carried out to evaluate the importance of flexible interplanar spacing in optimizing implants. New dose tables were generated to accommodate the frequent clinical need to minimize the number of catheter insertions.
Implants carried out in accordance with specified geometric constraints were found also to provide optimal dose homogeneity as determined using the volume ratio method with a flexible high dose limit. For two-plane implants, the interplanar spacing should be determined specifically in each case to ensure accurate target coverage. Calculations for specific cases showed that the tissue volume treated to unnecessarily high dose levels can be reduced by a large factor by careful positioning of the implant planes. A smaller ribbon and seed spacing will, in general, lead to better dose uniformity when this is evaluated in terms of the volumes treated to very high dose levels.
Our studies showed that implants carried out using simple and useful geometric guidelines will also provide an acceptably uniform dose distribution. For double plane implants, the separation of the implant planes should be optimized for each target thickness.
本研究采用体积比技术，在完全基于几何约束的平面组织间植入系统中检测剂量均匀性。探讨并讨论了确定可接受剂量变化上限的基本原理。根据其对剂量均匀性的影响，评估了带状间隔和平面间距离的变化。
针对一系列平面植入尺寸生成体积-剂量曲线。计算靶区内以及参考等剂量线和更高等剂量面之间所包含的体积，作为剂量均匀性的度量。进行均匀性、靶区覆盖和外部组织照射的研究，以评估灵活的平面间间距在优化植入中的重要性。生成新的剂量表，以满足临床减少导管插入次数的频繁需求。
发现按照特定几何约束进行的植入，在使用具有灵活高剂量限制的体积比方法确定时，也能提供最佳剂量均匀性。对于双平面植入，应针对每种情况具体确定平面间间距，以确保准确的靶区覆盖。特定病例的计算表明，通过仔细定位植入平面，可将接受不必要高剂量水平治疗的组织体积大幅减少。一般而言，当根据接受非常高剂量水平治疗的体积来评估时，较小的带状和籽源间距将导致更好的剂量均匀性。
我们的研究表明，使用简单且实用的几何指南进行植入，也能提供可接受的均匀剂量分布。对于双平面植入，应针对每个靶区厚度优化植入平面的间距。
