Higgins Patrick D, Gerbi Bruce J, Macedon Mark, Dusenbery Kathryn E
Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Appl Clin Med Phys. 2006 May 25;7(2):9-17. doi: 10.1120/jacmp.v7i2.2161.
In this report we discuss the application of a modified Gill-Thomas-Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproduceably position and treat the orbits of these children to between 2520 and 3960 cGy in 180 cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be +/- 2 mm. The overall average difference and standard deviation in measurement was 0.47 +/- 0.63 mm for the first case, and 0.19 +/- 0.94 mm for the second case with a combined average of 0.35 +/- 0.79 mm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics) incorporated a single isocenter for each orbit and 3-4 arcs per isocenter. Inter-comparisons have been made between this technique and a standard lateral field technique, designed using the SRS planning system. Dose-volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We have found that the NTCP is reduced from 95-100% in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia and reduces the chances of a poor cosmetic result in these growing children.
在本报告中，我们讨论了一种改良的吉尔-托马斯-科斯曼（GTC）可重新定位头架在婴儿麻醉下进行分次立体定向放射治疗（SRT）中的应用。该系统已用于治疗两名分别为12个月和18个月大的双侧视网膜母细胞瘤婴儿，使用的是瓦里安6/100直线加速器。GTC头架用于将这些儿童的眼眶可重复定位并治疗，剂量为2520至3960厘戈瑞，分180厘戈瑞的分次给予。一个标准的头颈托架及配套的热塑性面罩经过改装后安装到头架上，以实现这些治疗。我们发现，与初始拟合数据相比，重复固定时的最大平均偏差为±2毫米。第一例病例测量的总体平均差异和标准差为0.47±0.63毫米，第二例病例为0.19±0.94毫米，总共381个点测量的总体平均为0.35±0.79毫米。立体定向治疗计划（Radionics）为每个眼眶采用单个等中心，每个等中心有3至4个弧度。已将该技术与使用立体定向放射外科（SRS）计划系统设计的标准侧野技术进行了对比。已针对每种方法计算了眼眶骨区域的剂量-体积直方图以及基于儿童骨骼生长抑制的相应正常组织并发症概率（NTCP）。我们发现，标准治疗方法中的NTCP从95%至100%降至SRT时的16%或更低。使用改良头架可提供出色的摆位重复性，便于对患者进行麻醉，并减少这些正在成长的儿童出现不良美容效果的几率。
