Raaijmakers A J E, Hårdemark B, Raaymakers B W, Raaijmakers C P J, Lagendijk J J W
Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
Phys Med Biol. 2007 Dec 7;52(23):7045-54. doi: 10.1088/0031-9155/52/23/018. Epub 2007 Nov 15.
A combined system of a 6 MV linear accelerator and a 1.5 T MRI scanner is currently being developed. In this system, the patient will be irradiated in the presence of a 1.5 T magnetic field. This causes a strong dose increase at tissue-air interfaces. Around air cavities in the patient, these effects may become problematic. Homogeneous dose distributions can be obtained around regularly shaped symmetrical cavities using opposing beams. However, for more irregularly shaped cavities this approach may not be sufficient. This study will investigate whether IMRT can be used to cope with magnetic field dose effects, in particular for target volumes adjacent to irregularly shaped air cavities. Therefore, an inverse treatment planning approach has been designed based on pre-calculated beamlet dose distribution kernels. Using this approach, optimized dose distributions were calculated for B = 1.5 T and for B = 0 T. Investigated target sites include a prostate cancer, a laryngeal cancer and an oropharyngeal cancer. Differences in the dose distribution between B = 0 and 1.5 T were minimal; only the skin dose increased for B = 1.5 T. Homogeneous dose distributions were obtained for target structures adjacent to air cavities without the use of opposing beams. These results show that a 1.5 T magnetic field does not compromise the ability to achieve desired dose distributions with IMRT.
目前正在研发一种由6兆伏直线加速器和1.5特斯拉磁共振成像扫描仪组成的联合系统。在该系统中，患者将在1.5特斯拉磁场存在的情况下接受照射。这会在组织 - 空气界面处导致剂量大幅增加。在患者体内的气腔周围，这些影响可能会成为问题。使用对穿射束可以在规则形状的对称腔周围获得均匀的剂量分布。然而，对于形状更不规则的腔，这种方法可能并不足够。本研究将调查调强放射治疗（IMRT）是否可用于应对磁场剂量效应，特别是对于与不规则形状气腔相邻的靶区。因此，基于预先计算的子野剂量分布核设计了一种逆向治疗计划方法。使用这种方法，计算了B = 1.5特斯拉和B = 0特斯拉时的优化剂量分布。研究的靶区包括前列腺癌、喉癌和口咽癌。B = 0和1.5特斯拉之间的剂量分布差异很小；仅B = 1.5特斯拉时皮肤剂量增加。在不使用对穿射束的情况下，获得了与气腔相邻的靶结构的均匀剂量分布。这些结果表明，1.5特斯拉磁场不会损害调强放射治疗实现所需剂量分布的能力。
