Webster Gareth J, Rowbottom Carl G, Mackay Ranald I
North Western Medical Physics, Christie Hospital NHS Trust, Manchester, United Kingdom.
Med Dosim. 2009 Summer;34(2):99-106. doi: 10.1016/j.meddos.2008.05.001. Epub 2008 Jun 6.
Image-guided radiotherapy (IGRT) can potentially improve the accuracy of delivery of radiotherapy treatments by providing high-quality images of patient anatomy in the treatment position that can be incorporated into the treatment setup. The achievable accuracy and precision of delivery of highly complex head-and-neck intensity modulated radiotherapy (IMRT) plans with an IGRT technique using an Elekta Synergy linear accelerator and the Pinnacle Treatment Planning System (TPS) was investigated. Four head-and-neck IMRT plans were delivered to a semi-anthropomorphic head-and-neck phantom and the dose distribution was measured simultaneously by up to 20 microMOSFET (metal oxide semiconductor field-effect transmitter) detectors. A volumetric kilovoltage (kV) x-ray image was then acquired in the treatment position, fused with the phantom scan within the TPS using Syntegra software, and used to recalculate the dose with the precise delivery isocenter at the actual position of each detector within the phantom. Three repeat measurements were made over a period of 2 months to reduce the effect of random errors in measurement or delivery. To ensure that the noise remained below 1.5% (1 SD), minimum doses of 85 cGy were delivered to each detector. The average measured dose was systematically 1.4% lower than predicted and was consistent between repeats. Over the 4 delivered plans, 10/76 measurements showed a systematic error > 3% (3/76 > 5%), for which several potential sources of error were investigated. The error was ultimately attributable to measurements made in beam penumbrae, where submillimeter positional errors result in large discrepancies in dose. The implementation of an image-guided technique improves the accuracy of dose verification, particularly within high-dose gradients. The achievable accuracy of complex IMRT dose delivery incorporating image-guidance is within +/- 3% in dose over the range of sample points. For some points in high-dose gradients, submillimeter errors in position can lead to errors > 3%. The precision of the delivery system was demonstrated to be within the experimental noise of the detector system of 1.5% (1 SD).
图像引导放射治疗（IGRT）通过在治疗位置提供患者解剖结构的高质量图像，这些图像可纳入治疗设置中，从而有可能提高放射治疗的准确性。研究了使用医科达Synergy直线加速器和Pinnacle治疗计划系统（TPS）的IGRT技术，实施高度复杂的头颈调强放射治疗（IMRT）计划时可实现的准确性和精度。将四个头颈IMRT计划应用于一个半人体模型的头颈部位，并通过多达20个微型金属氧化物半导体场效应晶体管（microMOSFET）探测器同时测量剂量分布。然后在治疗位置采集容积千伏（kV）X射线图像，使用Syntegra软件在TPS内与模型扫描图像融合，并用于在模型内每个探测器的实际位置以精确的治疗等中心重新计算剂量。在两个月的时间内进行了三次重复测量，以减少测量或治疗中的随机误差影响。为确保噪声保持在1.5%（1标准差）以下，每个探测器的最小剂量为85 cGy。平均测量剂量系统地比预测值低1.4%，且重复测量之间一致。在4个实施的计划中，10/76次测量显示系统误差>3%（3/76>5%），对此研究了几个潜在的误差来源。该误差最终归因于在射束半影区进行的测量，在该区域亚毫米级的位置误差会导致剂量出现较大差异。图像引导技术的实施提高了剂量验证的准确性，特别是在高剂量梯度范围内。结合图像引导的复杂IMRT剂量输送在采样点范围内的剂量可实现的准确性在±3%以内。对于高剂量梯度中的某些点，位置上的亚毫米级误差可能导致误差>3%。输送系统的精度在探测器系统1.5%（1标准差）的实验噪声范围内得到了证明。
