Kinhikar Rajesh A, Master Zubin, Dhote Dipak S, Deshpande Deepak D
Department of Medical Physics, Tata Memorial Centre, Parel, Mumbai 400012, India.
J Med Phys. 2009 Apr;34(2):73-9. doi: 10.4103/0971-6203.51933.
A Helical Tomotherapy (HT) Hi-Art II (TomoTherapy, Inc., Madison, WI, USA) has been one of the important innovations to help deliver IMRT with image guidance. On-board, mega voltage computed tomography (MVCT) detectors are used for imaging and dosimetric purpose. The two objectives of this study are: (i) To estimate the dosimetric and general capability (TomoImage registration, reconstruction, contrast and spatial resolution, artifacts-free image and dose in TomoImage) of on-board MVCT detectors. (ii) To measure the dosimetric parameters (output and energy) following major repair. The MVCT detectors also estimated the rotational output constancy well. During this study, dosimetric tests were repeated after replacing MVCT detectors and the target. fixed-gantry/fixed-couch measurements were measured daily to investigate; the system stability. Thermoluminescense dosimeter (TLD) was used during both the measurements subsequently. The MVCT image quality with old and new detectors was comparable and hence acceptable clinically. The spatial resolution was optimal and the dose during TomoImage was 2 cGy (well within the manufacturer tolerance of 4 cGy). The results of lateral beam profiles showed an excellent agreement between the two normalized plots. The output from the rotational procedure revealed 99.7% while the energy was consistent over a period of twelve months. The Hi-Art II system has maintained its calibration to within +/- 2% and energy to within +/- 1.5% over the initial twelve-month period. Based on the periodic measurements for rotational output and consistency in the lateral beam profile shape, the on-board detector proved to be a viable dosimetric quality assurance tool for IMRT with Tomotherapy. Tomotherapy was stable from the dosimetric point of view during the twelve-month period.
螺旋断层放射治疗系统（HT）Hi-Art II（美国威斯康星州麦迪逊市的TomoTherapy公司）一直是有助于实现图像引导调强放射治疗（IMRT）的重要创新之一。机载兆伏级计算机断层扫描（MVCT）探测器用于成像和剂量测定目的。本研究的两个目标是：（i）评估机载MVCT探测器的剂量测定和总体性能（TomoImage配准、重建、对比度和空间分辨率、无伪影图像以及TomoImage中的剂量）。（ii）在重大维修后测量剂量学参数（输出和能量）。MVCT探测器对旋转输出稳定性的评估也很好。在本研究期间，更换MVCT探测器和靶区后重复进行剂量学测试，每天进行固定机架/固定治疗床测量以研究系统稳定性。随后在两次测量中均使用了热释光剂量计（TLD）。新旧探测器的MVCT图像质量具有可比性，因此在临床上是可接受的。空间分辨率最佳，TomoImage期间的剂量为2厘戈瑞（完全在制造商规定的4厘戈瑞公差范围内）。侧野剂量分布的结果显示两个归一化图之间具有极好的一致性。旋转程序的输出显示为99.7%，而能量在十二个月的时间内保持一致。在最初的十二个月期间，Hi-Art II系统的校准保持在+/- 2%以内，能量保持在+/- 1.5%以内。基于对旋转输出的定期测量以及侧野剂量分布形状的一致性，机载探测器被证明是用于螺旋断层放射治疗IMRT的可行的剂量学质量保证工具。从剂量学角度来看，螺旋断层放射治疗在十二个月期间是稳定的。
