Department of Mathematics, Linköping University, SE-58183, Linköping, Sweden.
Radiation Physics, Department of Medical and Health Sciences, Linköping University, SE-58183, Linköping, Sweden.
Med Phys. 2019 Jun;46(6):2556-2566. doi: 10.1002/mp.13533. Epub 2019 May 15.
High dose-rate brachytherapy is a method of radiotherapy for cancer treatment in which the radiation source is placed within the body. In addition to give a high enough dose to a tumor, it is also important to spare nearby healthy organs [organs at risk (OAR)]. Dose plans are commonly evaluated using the so-called dosimetric indices; for the tumor, the portion of the structure that receives a sufficiently high dose is calculated, while for OAR it is instead the portion of the structure that receives a sufficiently low dose that is of interest. Models that include dosimetric indices are referred to as dose-volume models (DVMs) and have received much interest recently. Such models do not take the dose to the coldest (least irradiated) volume of the tumor into account, which is a distinct weakness since research indicates that the treatment effect can be largely impaired by tumor underdosage even to small volumes. Therefore, our aim is to extend a DVM to also consider the dose to the coldest volume.
An improved DVM for dose planning is proposed. In addition to optimizing with respect to dosimetric indices, this model also takes mean dose to the coldest volume of the tumor into account.
Our extended model has been evaluated against a standard DVM in ten prostate geometries. Our results show that the dose to the coldest volume could be increased, while also computing times for the dose planning were improved.
While the proposed model yields dose plans similar to other models in most aspects, it fulfils its purpose of increasing the dose to cold tumor volumes. An additional benefit is shorter solution times, and especially for clinically relevant times (of minutes) we show major improvements in tumour dosimetric indices.
高剂量率近距离放射治疗是一种癌症治疗放射疗法，其中放射源被放置在体内。除了给予肿瘤足够高的剂量外，保护附近的健康器官[危险器官（OAR）]也很重要。剂量计划通常使用所谓的剂量学指标进行评估；对于肿瘤，计算接收足够高剂量的结构部分，而对于 OAR，则计算接收足够低剂量的结构部分。包括剂量学指标的模型称为剂量体积模型（DVM），最近受到了广泛关注。这些模型没有考虑到肿瘤最冷（受辐照最少）体积的剂量，这是一个明显的弱点，因为研究表明，即使是小体积的肿瘤剂量不足也会大大降低治疗效果。因此，我们的目标是扩展 DVM 以考虑到肿瘤最冷体积的剂量。
提出了一种用于剂量计划的改进 DVM。除了针对剂量学指标进行优化外，该模型还考虑了肿瘤最冷体积的平均剂量。
我们的扩展模型已在十个前列腺几何形状中针对标准 DVM 进行了评估。我们的结果表明，最冷体积的剂量可以增加，同时计算剂量计划的时间也得到了改善。
虽然该模型在大多数方面产生的剂量计划与其他模型相似，但它满足了增加冷肿瘤体积剂量的目的。另一个好处是解决方案时间更短，特别是对于临床相关的时间（分钟），我们在肿瘤剂量学指标方面取得了重大改进。
