Craciunescu O, Cai J, de Leeuw A, Kirisits C
Duke University Medical Center, Durham, NC.
University Medical Center Utrecht, Utrecht, The Netherlands.
Med Phys. 2012 Jun;39(6Part24):3913. doi: 10.1118/1.4735972.
Image-guidance plays an important role in modern radiation therapy, predominantly in external beam planning and delivery. In contrast, brachytherapy is still largely based on systems originally developed in the early 20th century. In recent years, with the advent of high/pulsed dose rate (HDR/PDR) afterloading technology, advanced treatment planning systems and CT and MRI compatible applicators, image-guided adaptive brachytherapy treatments are now achievable. With image guidance, the target can be delineated more precisely, resulting in delivering more controlled doses of radiation to the target while sparing surrounding healthy tissue. GEC-ESTRO guidelines are crucial for implementing robust and standardized image guided adaptive brachytherapy (IGABT). They rely on MRI-guided planning for cervical cancer. MRI can be performed for each brachytherapy (BT) fraction to adaptively plan and deliver the desired radiation dose with less toxicity to surrounding tissues. MR imaging has its advantages, but also challenges and limitations (image artifacts and distortion related to magnetic nonlinearity, MR sequence selection, accuracy of 3D applicator reconstruction) that need addressed. Moreover, MRI technology is not readily available in most Radiation Oncology departments, making its implementation hard. In such settings, CT or US-based planning can be used despite lacking the desired soft tissue resolution to accurately depict the target. Hybrid approaches have been proposed, where a first BT fraction is planed based on MRI, and subsequent fractions are performed with CT-guidance. Moreover, new intracavitary/interstitial applicators are becoming available and data from centers using existent applicators is maturing. Regardless of the type of adaptive image guided and applicators used, there are still ongoing debates regarding the prescription, the relevance of point A dose, treatment planning in general, and the use of inverse planning in particular, role of model-based dose calculation algorithms, adaptive strategies, intrafraction variability, in-vivo dosimetry, dose summation with external beam treatments, to mention just some of the challenges raised by implementing this treatment technique. This symposium is proposing to address all of these issues and update the community at large on the status of image guided adaptive brachytherapy for cervical cancer.
图像引导在现代放射治疗中发挥着重要作用，主要应用于外照射束的计划制定和治疗实施。相比之下，近距离放射治疗在很大程度上仍基于20世纪初开发的系统。近年来，随着高/脉冲剂量率（HDR/PDR）后装技术、先进的治疗计划系统以及与CT和MRI兼容的施源器的出现，图像引导的自适应近距离放射治疗现已成为可能。借助图像引导，可以更精确地勾勒靶区，从而在保护周围健康组织的同时，向靶区输送更精准控制的辐射剂量。GEC-ESTRO指南对于实施稳健且标准化的图像引导自适应近距离放射治疗（IGABT）至关重要。对于宫颈癌，这些指南依赖于MRI引导的计划制定。可以针对每次近距离放射治疗（BT）分次进行MRI检查，以便自适应地计划并输送所需的辐射剂量，同时减少对周围组织的毒性。MR成像有其优点，但也存在挑战和局限性（与磁非线性、MR序列选择、三维施源器重建的准确性相关的图像伪影和畸变），需要加以解决。此外，大多数放射肿瘤学科室并不容易获得MRI技术，这使得其实施困难。在这种情况下，尽管缺乏准确描绘靶区所需的软组织分辨率，但仍可使用基于CT或超声的计划制定方法。已经提出了混合方法，即基于MRI制定首次BT分次的计划，随后的分次在CT引导下进行。此外，新型腔内/组织间施源器不断涌现，使用现有施源器的中心的数据也在不断完善。无论使用何种类型的自适应图像引导和施源器，在处方、A点剂量的相关性、总体治疗计划，尤其是逆向计划的使用、基于模型的剂量计算算法的作用、自适应策略、分次内变异性、体内剂量测定、与外照射治疗的剂量总和等方面仍存在持续的争论，这只是实施这种治疗技术所引发的部分挑战。本次研讨会提议解决所有这些问题，并向广大同行介绍宫颈癌图像引导自适应近距离放射治疗的现状。
