Sloboda Ron S, Usmani N, Monajemi T T, Liu D M-C
Department of Medical Physics, Cross Cancer Institute, Alberta Health Services - Cancer Care and Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada.
J Med Phys. 2012 Apr;37(2):81-9. doi: 10.4103/0971-6203.94742.
This article summarizes current knowledge concerning the characterization of prostatic edema and intra-prostatic seed movement as these relate to dosimetry of permanent prostate implants, and reports the initial application to clinical data of a new edema model used in calculating pre- and post-implant dose distributions. Published edema magnitude and half-life parameters span a broad range depending on implant technique and measurement uncertainty, hence clinically applicable values should be determined locally. Observed intra-prostatic seed movements appear to be associated with particular aspects of implant technique and could be minimized by technique modification. Using an extended AAPM TG-43 formalism incorporating the new edema model, relative dose error RE associated with neglecting edema was calculated for three I-125 seed implants (18.9 cc, 37.6 cc, 60.2 cc) performed at our center. Pre- and post-plan RE average values and ranges in a 50 × 50 × 50 mm(3) calculation volume were similar at ~2% and ~0-3.5%, respectively, for all three implants; however, the spatial distribution of RE varied for different seed configurations. Post-plan values of D90 and V100 for prostate were reduced by ~2% and ~1%, respectively. In cases where RE is not clinically negligible as a consequence of large edema magnitude and / or use of Pd-103 seeds, the dose calculation method demonstrated here can be applied to account for edema explicitly and there by improve the accuracy of clinical dose estimates.
本文总结了有关前列腺水肿特征及前列腺内粒子移动与永久性前列腺植入剂量学关系的当前知识，并报告了一种用于计算植入前和植入后剂量分布的新水肿模型在临床数据中的初步应用。已发表的水肿程度和半衰期参数因植入技术和测量不确定性而跨度较大，因此临床适用值应在当地确定。观察到的前列腺内粒子移动似乎与植入技术的特定方面有关，可通过技术改进将其最小化。使用纳入新水肿模型的扩展AAPM TG - 43形式，针对在我们中心进行的三例I - 125粒子植入（18.9 cc、37.6 cc、60.2 cc），计算了因忽略水肿而产生的相对剂量误差RE。在一个50×50×50 mm³的计算体积中，所有三例植入的植入前和植入后RE平均值及范围分别相似，约为2%和约0 - 3.5%；然而，RE的空间分布因不同的粒子配置而有所不同。前列腺的植入后D90和V100值分别降低了约2%和约1%。在因水肿程度大及/或使用Pd - 103粒子导致RE在临床上不可忽略的情况下，此处展示的剂量计算方法可用于明确考虑水肿，从而提高临床剂量估计的准确性。
