Department of Radiation Oncology, Cancer Institute of New Jersey, New Brunswick, NJ 08903, USA.
J Appl Clin Med Phys. 2013 May 6;14(3):4138. doi: 10.1120/jacmp.v14i3.4138.
One of the main components in a Calypso 4D localization and tracking system is an electromagnetic array placed above patients that is used for target monitoring during radiation treatment. The beam attenuation and beam spoiling properties of the Calypso electromagnetic array at various beam angles were investigated. Measurements were performed on a Varian Clinac iX linear accelerator with 6 MV and 15 MV photon beams. The narrow beam attenuation properties were measured under a field size of 1 cm × 1 cm, with a photon diode placed in a cylindrical graphite buildup cap. The broad beam attenuation properties were measured under a field size of 10 cm × 10 cm, with a 0.6 cc cylindrical Farmer chamber placed in a polystyrene buildup cap. Beam spoiling properties of the array were studied by measuring depth-dose change from the array under a field size of 10 cm × 10 cm in a water-equivalent plastic phantom with an embedded Markus parallel plate chamber. Change in depth doses were measured with the array placed at distances of 2, 5, and 10 cm from the phantom surface. Narrow beam attenuation and broad beam attenuation from the array were found to be less than 2%-3% for both 6 MV and 15 MV beams at angles less than 40°, and were more pronounced at more oblique angles. Spoiling effects are appreciable at beam buildup region, but are insignificant at depths beyond dmax. Dose measurements in a QA phantom using patient IMRT and VMAT treatment plans were shown to have less than 2.5% dose difference with the Calypso array. The results indicate that the dose difference due to the placement of Calypso array is clinically insignificant.
Calypso 4D 定位和跟踪系统的主要组成部分之一是放置在患者上方的电磁阵列，用于放射治疗期间的目标监测。研究了 Calypso 电磁阵列在不同射束角度下的束衰减和束散射线特性。在配备有 6 MV 和 15 MV 光子束的瓦里安 Clinac iX 线性加速器上进行了测量。在 1 cm×1 cm 的射野尺寸下，使用放置在圆柱形石墨堆积帽中的光子二极管测量窄束衰减特性。在 10 cm×10 cm 的射野尺寸下，使用放置在聚苯乙烯堆积帽中的 0.6 cc 圆柱形 Farmer 室测量宽束衰减特性。通过在水等效塑料体模中测量具有嵌入式 Markus 平行板室的 10 cm×10 cm 射野尺寸下从阵列下的深度剂量变化来研究阵列的散射线特性。在距体模表面 2、5 和 10 cm 的位置放置阵列时，测量深度剂量的变化。在小于 40°的角度下，对于 6 MV 和 15 MV 射线，从阵列的窄束衰减和宽束衰减均小于 2%-3%，在更倾斜的角度下更为明显。在束累积区域，散射线的影响是明显的，但在 dmax 以外的深度上则不明显。使用患者的 IMRT 和 VMAT 治疗计划在 QA 体模中的剂量测量结果表明，与 Calypso 阵列相比，剂量差异小于 2.5%。结果表明，由于放置 Calypso 阵列而导致的剂量差异在临床上无足轻重。
