Røthe Arnesen Marius, Eilertsen Karsten, Malinen Eirik
Department of Medical Physics, Division of Cancer Medicine and Radiotherapy, Rikshospitalet University Hospital, Oslo, Norway.
Acta Oncol. 2008;47(7):1373-81. doi: 10.1080/02841860802244190.
To present a methodology to estimate optimal treatment margins for radiotherapy of prostate cancer based on interfraction imaging.
Cone beam CT images of a prostate cancer patient undergoing fractionated radiotherapy were acquired at all treatment sessions. The clinical target volume (CTV) and organs at risk (OARs; bladder and rectum) were delineated in the images. Random sampling from the CTV-OAR library was performed in order to simulate fractionated radiotherapy including intra- and interpatient variability in setup and organ motion/deformation. For each simulated patient, four treatment fields defined by multileaf collimators were automatically generated around the planning CTV. The treatment margin (the distance from the CTV to the field border) was varied between 2.5 and 20 mm. Resulting dose distributions were calculated by a convolution method. Doses to OARs were reconstructed by polynomial warping, while the CTV was assumed to be a rigid body. The equivalent uniform dose (EUD), the tumor control probability (TCP) and the normal tissue complication probability (NTCP) were used to estimate the clinical effect. Patient repositioning strategies at treatment were compared.
The simulations produced population based EUD histograms for the CTV and the OARs. The number of patients receiving an optimal target EUD increased with increasing margins, but at the cost of an increasing number receiving a high EUD to the OARs. Calculations of the probability of complication-free tumor control and subsequent analysis gave an optimal treatment margin of about 10mm for the simulated population, if no correction strategy was undertaken.
The current work illustrates the principle of optimal treatment margins based on interfraction imaging. Clinically applicable margins may be obtained if a large patient image database is available.
提出一种基于分次治疗间成像来估计前列腺癌放射治疗最佳治疗边界的方法。
在所有治疗疗程中获取一名接受分次放射治疗的前列腺癌患者的锥形束CT图像。在图像中勾勒出临床靶区（CTV）和危及器官（OARs；膀胱和直肠）。从CTV - OAR库中进行随机抽样，以模拟包括摆位以及器官运动/变形的患者内和患者间变异性的分次放射治疗。对于每个模拟患者，围绕计划CTV自动生成由多叶准直器定义的四个治疗野。治疗边界（从CTV到野边界的距离）在2.5至20毫米之间变化。通过卷积方法计算所得剂量分布。通过多项式变形重建OARs的剂量，而CTV被假定为刚体。使用等效均匀剂量（EUD）、肿瘤控制概率（TCP）和正常组织并发症概率（NTCP）来估计临床效果。比较了治疗时的患者重新摆位策略。
模拟生成了基于群体的CTV和OARs的EUD直方图。接受最佳靶区EUD的患者数量随着边界增加而增加，但代价是接受高剂量OARs的患者数量增加。无并发症肿瘤控制概率的计算及后续分析得出，如果不采取校正策略，模拟群体的最佳治疗边界约为10毫米。
当前工作阐述了基于分次治疗间成像的最佳治疗边界原理。如果有大型患者图像数据库，可能获得临床适用的边界。
