Stathakis Sotirios, Mavroidis Panayiotis, Narayanasamy Ganesh, Markovic Miljenko, Myers Pamela, Papanikolaou Niko
Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, TX, USA.
J BUON. 2015 Jul-Aug;20(4):1154-63.
Five patients with 38 fields have been analyzed in this study. The plans were optimized for the following clinical sites: one liver, one lung, one brain, one prostate and one spine. The detector array used for the measurements was the PTW Seven29 array. All the plans were optimized and calculated using Eclipse v8.9. The center of the array was setup at 215 cm from the source and all the fields were measured and analyzed one by one. All the 30 measurements were performed on a NovalisTX linear accelerator equipped with a high definition multileaf collimator. The evaluation was based mainly on gamma index passing rates using 2 mm distance to agreement (DTA) and 2% dose difference.
The accuracy of the Eclipse Treatment Planning System (TPS) at extended Source to Surface Distances (SSDs) using an ionization chamber was measured to be within 1.0%. All the field measurements were performed and analyzed 35 individually. The percent of the points that had a gamma index of less than 1 using 3%/3 mm was >99% for all the measurements. In order to better evaluate our process and distinguish smaller differences a new set of results was obtained by applying gamma index tolerances of 2%/2mm. In this case, the gamma index passing rates ranged from 90.8 to 100% (95.5%±3%). The profile comparison showed that the detector array measurements followed closely the calculated 40 profiles, even for fields optimized with multiple peaks and valleys.
The choice of the IMRT QA device has an important role in the results of the patient specific QA of the delivered dose to the patient in the case of small targets as in the treatment of spinal targets. In this study, we demonstrated that an extended SSD measurement can improve the sampling resolution of a two-dimensional (2D) detector array, in our case the PTW 45 Seven29 array. This method was shown to be accurate and efficient for measuring highly modulated small fields for pre-treatment patient specific QA.
本研究分析了5例患者的38个射野。计划针对以下临床部位进行优化：一个肝脏、一个肺、一个脑、一个前列腺和一个脊柱。用于测量的探测器阵列是PTW Seven29阵列。所有计划均使用Eclipse v8.9进行优化和计算。将阵列中心设置在距源215 cm处，对所有射野逐一进行测量和分析。所有30次测量均在配备高清多叶准直器的NovalisTX直线加速器上进行。评估主要基于使用2 mm距离一致性（DTA）和2%剂量差异的伽马指数通过率。
使用电离室测量Eclipse治疗计划系统（TPS）在延长源皮距（SSD）时的精度在1.0%以内。对所有射野测量并单独分析了35次。对于所有测量，使用3%/3 mm时伽马指数小于1的点的百分比>99%。为了更好地评估我们的流程并区分较小差异，通过应用2%/2 mm的伽马指数公差获得了一组新结果。在这种情况下，伽马指数通过率在90.8%至100%之间（95.5%±3%）。剖面比较表明，即使对于具有多个峰谷的优化射野，探测器阵列测量也与计算剖面紧密跟随。
在治疗脊柱等小靶区的情况下，调强放疗质量保证（QA）设备的选择对患者特定剂量传递的QA结果具有重要作用。在本研究中，我们证明了延长SSD测量可以提高二维（2D）探测器阵列（在我们的案例中为PTW Seven29阵列）的采样分辨率。该方法被证明对于测量高度调制的小射野以进行治疗前患者特定QA是准确且有效的。
