Ma L, Kwok Y, Chin L S, Yu C, Regine W F
University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Phys Med Biol. 2005 Nov 21;50(22):5217-27. doi: 10.1088/0031-9155/50/22/001. Epub 2005 Oct 24.
Dedicated linac-based radiosurgery has been reported for trigeminal neuralgia treatments. In this study, we investigated the dose fall-off characteristics and setup error tolerance of linac-based radiosurgery as compared with standard Gamma Knife radiosurgery. In order to minimize the errors from different treatment planning calculations, consistent imaging registration, dose calculation and dose volume analysis methods were developed and implemented for both Gamma Knife and linac-based treatments. Intra-arc setup errors were incorporated into the treatment planning process of linac-based deliveries. The effects of intra-arc setup errors with increasing number of arcs were studied and benchmarked against Gamma Knife deliveries with and without plugging patterns. Our studies found equivalent dose fall-off properties between Gamma Knife and linac-based radiosurgery given a sufficient number of arcs (>7) and small intra-arc errors (<0.5 mm) were satisfied for linac-based deliveries. Increasing the number of arcs significantly decreased the variations in the dose fall-off curve at the low isodose region (e.g. from 40% to 10%) and also improved dose uniformity at the high isodose region (e.g. from 70% to 90%). As the number of arcs increased, the effects of intra-arc setup errors on the dose fall-off curves decreased. Increasing the number of arcs also reduced the integral dose to the distal normal brain tissues. In conclusion, linac-based radiosurgery produces equivalent dose fall-off characteristics to Gamma Knife radiosurgery with a high number of arcs. However, one must note the increased treatment time for a large number of arcs and isocentre accuracies.
已有报道使用专用直线加速器进行三叉神经痛的放射外科治疗。在本研究中，我们调查了直线加速器放射外科与标准伽玛刀放射外科相比的剂量衰减特性和摆位误差容忍度。为了尽量减少不同治疗计划计算产生的误差，针对伽玛刀和直线加速器治疗开发并实施了一致的影像配准、剂量计算和剂量体积分析方法。将弧形内摆位误差纳入直线加速器治疗的治疗计划过程中。研究了弧形内摆位误差随弧形数量增加的影响，并与有和没有插塞模式的伽玛刀治疗进行了对比。我们的研究发现，当直线加速器治疗满足足够数量的弧形（>7）和较小的弧形内误差（<0.5毫米）时，伽玛刀和直线加速器放射外科的剂量衰减特性相当。增加弧形数量显著降低了低等剂量区（如从40%到10%）剂量衰减曲线的变化，同时也改善了高等剂量区（如从70%到90%）的剂量均匀性。随着弧形数量的增加，弧形内摆位误差对剂量衰减曲线的影响减小。增加弧形数量还减少了远端正常脑组织的积分剂量。总之，直线加速器放射外科在大量弧形的情况下产生与伽玛刀放射外科相当的剂量衰减特性。然而，必须注意大量弧形会增加治疗时间以及等中心精度问题。
