Acun-Bucht Hediye, Tuncay Ebru, Darendeliler Emin, Kemikler Gönül
Harran University, Faculty of Medicine, Department of Biophysics, Osmanbey Campus, 63300 Sanliurfa, Turkey.
Ministry of Health, İstanbul Research and Training Hospital, Samatya, İstanbul, Turkey.
Rep Pract Oncol Radiother. 2018 Jul-Aug;23(4):242-250. doi: 10.1016/j.rpor.2018.04.001. Epub 2018 May 19.
This study aims at examining absolute dose verification of step-and-shoot intensity modulated radiation treatment (IMRT) of prostate and brain patients by use of ion chambers of two different volumes and thermoluminescent detectors (TLD).
The volume of the ion chamber (IC) is very important for absolute dose verification of IMRT plans since the IC has a volume average effect. With TLD detectors absolute dose verification can be done measuring the dose of multiple points simultaneously.
Ion chambers FC65-P of volume 0.65 cc and semiflex of volume 0.125 cc as well as TLDs were used to measure the central axis absolute dose of IMRT quality assurance (QA) plans. The results were compared with doses calculated by a treatment planning system (TPS). The absolute doses of off axis points located 2 cm and 4 cm away from the isocenter were measured with TLDs.
The measurements of the 0.125 cc ion chamber were found to be closer to TPS calculations compared to the 0.65 cc ion chamber, for both patient groups. For both groups the root mean square (RMS) differences between doses of the TPS and the TLD detectors are within 3.0% for the central axis and points 2 cm away from the isocenter of each axis. Larger deviations were found at the field edges, which have steep dose gradient.
The 0.125 cc ion chamber measures the absolute dose of the isocenter more accurately compared to the 0.65 cc chamber. TLDs have good accuracy (within 3.0%) for absolute dose measurements of in-field points.
本研究旨在使用两种不同体积的电离室和热释光探测器（TLD）对前列腺癌和脑癌患者的静态调强放射治疗（IMRT）进行绝对剂量验证。
电离室（IC）的体积对于IMRT计划的绝对剂量验证非常重要，因为电离室具有体积平均效应。使用TLD探测器可以通过同时测量多个点的剂量来进行绝对剂量验证。
使用体积为0.65 cc的FC65-P电离室、体积为0.125 cc的半柔性电离室以及TLD来测量IMRT质量保证（QA）计划的中心轴绝对剂量。将结果与治疗计划系统（TPS）计算的剂量进行比较。使用TLD测量距离等中心2 cm和4 cm处的离轴点的绝对剂量。
对于两个患者组，发现0.125 cc电离室的测量结果比0.65 cc电离室更接近TPS计算值。对于两个组，TPS剂量与TLD探测器剂量之间的均方根（RMS）差异在中心轴和距各轴等中心2 cm处的点上均在3.0%以内。在剂量梯度陡峭的野边缘发现了较大偏差。
与0.65 cc电离室相比，0.125 cc电离室测量等中心绝对剂量更准确。TLD对野内点的绝对剂量测量具有良好的准确性（在3.0%以内）。
