Dohlmar Frida, Morén Björn, Sandborg Michael, Larsson Torbjörn, Carlsson Tedgren Åsa
Medical Radiation Physics, Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden.
Center for Medical Image Science and Visualization, CMIV, Linköping University.
Phys Imaging Radiat Oncol. 2024 Nov 10;32:100672. doi: 10.1016/j.phro.2024.100672. eCollection 2024 Oct.
Manual treatment planning for cervical brachytherapy is a challenging task; therefore, we investigated a method for inverse treatment planning using pseudo-structures to control the dwell distribution. Our hypothesis was that this method could produce treatment plans with a pear-shaped dose distribution and a high central dose, that comply with clinical constraints.
Data from 16 previously treated patients were used to compare three treatment planning methods: i) manual, ii) straightforward inverse, and iii) inverse with pseudo-structures. The treatment plans were compared using dose-volume histogram parameters and by analysing the dwell times, and the distribution of total reference air-kerma (TRAK) in the different parts of the applicator. Methods were evaluated in one treatment planning system and verified in a second treatment planning system.
The median dose to 90 % of the clinical tumor volume was 7.6 Gy, 7.8 Gy and 8.1 Gy for manual, pseudo-structure and straightforward methods respectively. Distribution of TRAK for the different parts of the applicator for the three methods (manual, pseudo-structures, and straightforward), with combined intracavitary and interstitial treatments, were for vaginal part 39 %, 33 % and 15 %, for intra-uterine part 47 %, 50 % and 47 % and for interstitial part 13 %, 17 % and 38 % respectively. The results were similar in the second treatment planning system.
The developed pseudo-structures worked as intended in shaping the dwell time distribution and in meeting the clinical constraints for both investigated treatment planning systems.
宫颈癌近距离治疗的手动治疗计划是一项具有挑战性的任务；因此，我们研究了一种使用伪结构来控制驻留分布的逆向治疗计划方法。我们的假设是，这种方法可以产生具有梨形剂量分布和高中心剂量且符合临床约束的治疗计划。
使用来自16例先前接受治疗患者的数据来比较三种治疗计划方法：i）手动，ii）直接逆向，以及iii）带有伪结构的逆向。使用剂量体积直方图参数并通过分析驻留时间以及施源器不同部位的总参考空气比释动能（TRAK）分布来比较治疗计划。在一个治疗计划系统中对方法进行评估，并在第二个治疗计划系统中进行验证。
对于临床靶体积的90%，手动、伪结构和直接方法的中位剂量分别为7.6 Gy、7.8 Gy和8.1 Gy。对于三种方法（手动、伪结构和直接），在腔内和组织间联合治疗时，施源器不同部位的TRAK分布分别为：阴道部分39%、33%和15%，子宫内部分47%、50%和47%，组织间部分13%、17%和38%。在第二个治疗计划系统中的结果相似。
所开发的伪结构在塑造驻留时间分布以及满足两个研究治疗计划系统的临床约束方面按预期发挥了作用。
