Cunha Adam, Siauw Timmy, Hsu I-Chow, Pouliot Jean
Radiation Oncology, University of California, San Francisco, CA 94115.
Radiation Oncology, University of California, San Francisco, CA 94115.
Brachytherapy. 2016 Mar-Apr;15(2):246-51. doi: 10.1016/j.brachy.2015.10.009. Epub 2015 Dec 22.
To present the algorithm of a modification to the inverse planning simulated annealing (IPSA) optimization engine that allows for restriction of the intracatheter dwell time variance.
IPSA was modified to allow user control of dwell time variance within each catheter through a single parameter, the dwell time deviation constraint (DTDC). The minimum DTDC value (DTDC = 0) does not impose any restriction on dwell time variance, and the maximum value (DTDC = 1) restricts all dwell times within each catheter to take on the same value. The final optimization penalty function value was evaluated as a function of DTDC.
The algorithm proposed fully preserves the inverse planning nature of the IPSA algorithm along with the penalty-based dose optimization workflow. Increasing DTDC creates less variance in dwell time between dwell positions in each catheter and may be used to induce a more smooth change in dwell time with dwell position in each catheter. Nonzero DTDC values always increased the optimization penalty function value.
The DTDC was developed as an extension to IPSA to allow restriction of the difference in dwell time between adjacent dwell positions. This results in less variation between neighboring dwell positions which can be clinically desirable. However, the impact of this restriction needs to be considered for its clinical relevance on a case-by-case basis because considerable degradation in dose-volume histogram metrics can result for large DTDC values.
介绍一种对逆向计划模拟退火（IPSA）优化引擎的改进算法，该算法可限制导管内驻留时间的差异。
对IPSA进行了修改，以允许用户通过单个参数——驻留时间偏差约束（DTDC）来控制每个导管内的驻留时间差异。最小DTDC值（DTDC = 0）对驻留时间差异不施加任何限制，而最大值（DTDC = 1）则将每个导管内的所有驻留时间限制为相同的值。最终优化惩罚函数值作为DTDC的函数进行评估。
所提出的算法完全保留了IPSA算法的逆向计划性质以及基于惩罚的剂量优化工作流程。增加DTDC会使每个导管内驻留位置之间的驻留时间差异减小，并且可用于使每个导管内的驻留时间随驻留位置产生更平滑的变化。非零DTDC值总是会增加优化惩罚函数值。
DTDC是作为IPSA的扩展而开发的，用于限制相邻驻留位置之间的驻留时间差异。这会导致相邻驻留位置之间的变化更小，这在临床上可能是可取的。然而，由于较大的DTDC值可能会导致剂量体积直方图指标出现相当大的退化，因此需要根据具体情况考虑这种限制对其临床相关性的影响。
