Dewitt Kelly D, Hsu I Chow Joe, Speight Joycelyn, Weinberg Vivian K, Lessard Etienne, Pouliot Jean
Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA 94143-170, USA.
Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1270-4. doi: 10.1016/j.ijrobp.2005.07.972.
Three-dimensional treatment planning systems and inverse planning optimization for brachytherapy are becoming commercially available. Guidelines for target delineation and dose constrictions have not been established using this new software. In this study we describe a method of target delineation for the tandem and ovoids applicator. We then compare inverse planning dose distributions with the traditional methods of prescribing dose.
Target and organ-at-risk volumes were defined using systematic guidelines on 15 patients treated in our department with high-dose-rate brachytherapy for cervical cancer using tandem and ovoids. High-dose-rate distributions were created according to three different dose optimization protocols: inverse planning simulated annealing (IPSA), point A, and point A with a normalization of 2 cc of the bladder receiving 80% of the dose (bladder-sparing method). An uniform cost function for dose constraints was applied to all IPSA generated plans, and no manual optimization was allowed for any planning method.
Guidelines for target and structure-at-risk volumes, as well as dose constraint cost functions, were established. Dose-volume histogram analysis showed that the IPSA algorithm indicated no difference in tumor coverage compared with point A optimization while decreasing dose to the bladder and rectum. The IPSA algorithm provided better target volume coverage compared with bladder-sparing method with equivalent doses to the bladder and rectum.
This study uses a systematic approach for delineating target and organ-at-risk volumes and a uniform cost function for generating IPSA plans for cervical cancer using tandem and ovoids. Compared with conventional dose prescription methods, IPSA provides a consistent method of optimization that maintains or improves target coverage while decreasing dose to normal structures. Image-guided brachytherapy and inverse planning improve brachytherapy dosimetry.
三维治疗计划系统及近距离放射治疗的逆向计划优化正逐渐商业化。使用这种新软件尚未建立靶区勾画和剂量限制的指南。在本研究中，我们描述了一种针对串联和卵圆形施源器的靶区勾画方法。然后我们将逆向计划剂量分布与传统的处方剂量方法进行比较。
使用系统指南定义15例在我们科室接受串联和卵圆形施源器高剂量率近距离放射治疗宫颈癌患者的靶区和危及器官体积。根据三种不同的剂量优化方案创建高剂量率分布：逆向计划模拟退火（IPSA）、A点以及膀胱接受80%剂量的2cc归一化的A点（膀胱保护法）。对所有IPSA生成的计划应用统一的剂量约束成本函数，且任何计划方法均不允许手动优化。
建立了靶区和危及结构体积的指南以及剂量约束成本函数。剂量体积直方图分析表明，与A点优化相比，IPSA算法在肿瘤覆盖方面无差异，同时降低了膀胱和直肠的剂量。与膀胱保护法相比，IPSA算法在膀胱和直肠剂量相当的情况下提供了更好的靶区体积覆盖。
本研究采用系统方法勾画靶区和危及器官体积，并使用统一的成本函数为宫颈癌患者使用串联和卵圆形施源器生成IPSA计划。与传统剂量处方方法相比，IPSA提供了一种一致的优化方法，在减少正常结构剂量的同时维持或改善靶区覆盖。图像引导近距离放射治疗和逆向计划改善了近距离放射治疗剂量学。
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