Bahena J H, Martinez A, Yan D, Mele E, Edmunson G, Brown D, Hardy M, Brabbins D, Gustafson G
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073, USA.
Int J Radiat Oncol Biol Phys. 1998 Apr 1;41(1):13-9. doi: 10.1016/s0360-3016(98)00026-1.
High-dose rate (HDR) applicators for uterine cervix brachytherapy are used with increasing frequency. Because multiple HDR fractions are required for treatment, the applicator position reproducibility is of most importance. To study this effect, the clinical data from patients with uterine cervix cancer were examined retrospectively to evaluate the interfraction geometric variation of the HDR applicator and its potential treatment impact.
Eighteen patients with invasive cervical cancer who were treated with definitive radiotherapy at William Beaumont Hospital were included in the study. Patients were treated with 45-50.4 Gy megavoltage external beam to the pelvis, and 35 Gy to the prescription point A from 7 fractions of HDR brachytherapy. The 3-dimensional (3D) interfraction geometrical variation of the ring and tandem (R & T) applicator was measured using predefined reference points in the 7 sets of orthogonal simulation films obtained prior to each HDR application. Spatial reproducibility of the R & T insertion and time-trend of the R & T position variation related to patient's anatomy during the treatment course were analyzed with respect to different groups of patients who had either early or advanced disease.
The translational variation of the applicator position for all patients was 6.5, 5.9, and 7.7 mm (one standard deviation), respectively, in the patient's superior-to-inferior (SI), right-to-left lateral (RL), and anterior-to-posterior (AP) direction. The rotational variation was 3.4, 4.6, and 6.0 degrees (one standard deviation) in the patient's coronal, transverse, and sagittal planes. When the patients were grouped based on early disease or advanced disease, the latter demonstrated substantially larger variation (factor of 2) in the applicator position than the former. Furthermore, the time-trend of position variation was observable for both groups of patients. The variations occurred primarily during the first 3 fractions.
Based on the good spatial reproducibility observed in our study, the current clinical procedure for the HDR R & T applicator placement is reliable. Positional reproducibility of the R & T applicator is highly dependent upon the size of tumor volume, which, in turn, deviates the applicator during the early course of HDR brachytherapy. Attention to the construction of the midline block is of paramount importance.
高剂量率（HDR）施源器用于子宫颈近距离放射治疗的频率日益增加。由于治疗需要多个HDR分次，施源器位置的可重复性至关重要。为研究此效应，对子宫颈癌患者的临床数据进行回顾性检查，以评估HDR施源器的分次间几何变化及其潜在的治疗影响。
本研究纳入了18例在威廉·博蒙特医院接受根治性放疗的浸润性宫颈癌患者。患者接受45 - 50.4 Gy的兆伏级盆腔外照射，以及从7次HDR近距离放疗至处方点A的35 Gy剂量。在每次HDR照射前获得的7组正交模拟胶片中，使用预定义的参考点测量环形和串联（R & T）施源器的三维（3D）分次间几何变化。针对患有早期或晚期疾病的不同患者组，分析了R & T插入的空间可重复性以及治疗过程中R & T位置相对于患者解剖结构的时间趋势。
所有患者施源器位置在患者的头脚方向（SI）、左右方向（RL）和前后方向（AP）的平移变化分别为6.5、5.9和7.7毫米（一个标准差）。在患者的冠状面、横断面和矢状面的旋转变化分别为3.4、4.6和6.0度（一个标准差）。当根据早期疾病或晚期疾病对患者进行分组时，后者施源器位置的变化比前者大得多（2倍）。此外，两组患者均观察到位置变化的时间趋势。变化主要发生在前3次分次期间。
基于我们研究中观察到的良好空间可重复性，当前HDR R & T施源器放置的临床程序是可靠的。R & T施源器的位置可重复性高度依赖于肿瘤体积大小，而肿瘤体积大小又会在HDR近距离放疗的早期过程中使施源器发生偏移。重视中线挡铅的构建至关重要。
