Azhar Deeba, Gul Attia, Javid Muhamad Arshad, Hussain Muhammad Mubashar, Shehzadi Nazia Neelam
Department of Basic Sciences, University of Engineering and Technology, Taxila, 47080, Pakistan.
Institute of Nuclear Medicine, Oncology and Radiotherapy (INOR), Abbottabad, 22010, Pakistan.
Radiat Environ Biophys. 2023 Mar;62(1):83-96. doi: 10.1007/s00411-022-01008-x. Epub 2022 Dec 15.
The present study is aimed at exploring different scanning parameters, detectors and their orientations for time-efficient and accurate commissioning of a 6 MV clinical linear accelerator (LINAC). Beam profiles and percentage depth dose (PDD) curves were measured with a PTW dosimetry diode, a PTW Semiflex and a PinPoint ion chamber in different orientations. To acquire beam data, equidistant (step size of 0.5 mm, 1 mm, 2 mm and 3 mm) and fanline (step size of 2-0.5 mm, 2-1 mm, 3-0.5 mm and 3-1 mm) scanning modes were employed and data measurement time was recorded. Scan time per measurement point was also varied (0.2 s, 0.5 s and 1.0 s) to investigate its effect on the accuracy and acquisition time of beam data. Accuracy of the measured data was analyzed on the basis of the variation between measured data and data modeled by a treatment planning system. Beam profiles (particularly in penumbra region) were found to be sensitive to variation in scanning resolution and showed an improved accuracy with decrease in step size, while PDD curves were affected negligibly. The accuracy of beam data obtained with the PTW dosimetry diode and the PinPoint ion chamber was higher than those obtained with the PTW Semiflex ion chamber for small fields (2 × 2 cm and 3 × 3 cm). However, the response of the PTW diode and the PinPoint ion chamber was significantly indifferent in these fields. Furthermore, axial orientation of the PTW Semiflex ion chamber improved accuracy of profiles and PDDs as compared to radial orientation, while such a difference was not significant for the PinPoint ion chamber. It is concluded that a scan time of 0.2 s/point with a fanline scanning resolution of 2-1 mm for beam profiles and 3 mm for PDDs are most favorable in terms of accuracy and time efficiency. For small fields (2 × 2 cm and 3 × 3 cm), a PinPoint ion chamber in radial orientation or a dosimetry diode in axial orientation are recommended for both beam profiles and PDDs. If a PinPoint ion chamber and a PTW dosimetry diode are not available, a Semiflex ion chamber in axial orientation may be used for small fields.
本研究旨在探索不同的扫描参数、探测器及其取向，以便高效且准确地对一台6兆伏临床直线加速器（LINAC）进行调试。使用PTW剂量测定二极管、PTW半柔性电离室和针点电离室在不同取向测量射野剂量分布和百分深度剂量（PDD）曲线。为获取射束数据，采用了等间距（步长为0.5毫米、1毫米、2毫米和3毫米）和扇线（步长为2 - 0.5毫米、2 - 1毫米、3 - 0.5毫米和3 - 1毫米）扫描模式，并记录数据测量时间。每个测量点的扫描时间也有所变化（0.2秒、0.5秒和1.0秒），以研究其对射束数据准确性和采集时间的影响。基于测量数据与治疗计划系统建模数据之间的差异分析测量数据的准确性。发现射野剂量分布（尤其是在半值层区域）对扫描分辨率的变化敏感，并且随着步长减小准确性提高，而PDD曲线受影响可忽略不计。对于小射野（2×2厘米和3×3厘米），使用PTW剂量测定二极管和针点电离室获得的射束数据准确性高于使用PTW半柔性电离室获得的数据。然而，在这些射野中，PTW二极管和针点电离室的响应明显不同。此外，与径向取向相比，PTW半柔性电离室的轴向取向提高了射野剂量分布和PDD的准确性，而对于针点电离室，这种差异不显著。得出结论，就准确性和时间效率而言，对于射野剂量分布，扫描分辨率为2 - 1毫米、每个点扫描时间为0.2秒，对于PDD，扫描分辨率为3毫米是最有利的。对于小射野（2×2厘米和3×3厘米），对于射野剂量分布和PDD，建议使用径向取向的针点电离室或轴向取向的剂量测定二极管。如果没有针点电离室和PTW剂量测定二极管，轴向取向的半柔性电离室可用于小射野。
