N-isopropylacrylamide gel dosimeter to evaluate clinical photon beam characteristics

The introduction of beam intensity control concept in current radiotherapy techniques has increased treatment planning complexity. Thus, small-field dose measurement has become increasingly vital. Polymer gel dosimetry method is widely studied. It is the only dose measurement tool that provides 3D dose distribution. This study aims to use an N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3×3 and 4×4 cm². Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and Gafchromic^TM EBT3 radiochromic film displayed high consistency in the region deeper than the build-up region. The gel dosimeter dose profile had 3% lower flatness and symmetry measurement at 5 cm depth for different fields compared with that of the Gafchromic^TM EBT3 film. During gamma evaluation under 3%/3 mm dose difference/distance-to-agreement standard, the pass rates of the polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Given that the gel is tissue equivalent, it did not exhibit the energy dependence problems of radiochromic films. Therefore, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification.     

Flatness characteristics for diagonal scans from Varian and Siemens linear accelerators

The advent of 3D treatment planning systems whose algorithms utilize diagonal scan data to perform dose calculations has made the collection of diagonal profile data essential. Manufacturers' specifications (MS) on beam flatness and symmetry apply to both the radial and transverse axes of all square field sizes from 10 × 10 cm² to the largest field available. Beam profile measurements were obtained for both diagonal axes over a range of field sizes and depths for two units, a Varian 2100C and a Siemens KD. In this note the International Electrotechnical Commission (IEC) flatness definition was used to characterize the diagonal flatness of each beam.     

对国标《医用电子加速器性能和试验方法(草案定稿)》中“射野均整区域”规定的探讨

对国标《医用电子加速器性能和试验方法（草案定稿）》中“射野均整区域”的规定进行了探讨，指出了该规定有失科学性与严谨性，不便于与国际通用规定接轨，在实际测量中也不易把握。提出了规定“射野平坦区域”的新建议，给出了测量点处实际射野宽度和平坦区域的确定方法，并加以实验验证。     

四种常见加速器晨检仪的性能比较

目的 比较4种常见直线加速器晨检仪的性能差异.方法 用三维水箱、剂量仪和电离室测量并调整直线加速器剂量学参数,确保加速器的束流系统基本稳定,包括中心轴输出量(CAX)、射野平坦度(FLAT)和射野对称性(SYM).对4种晨检仪LINA-C、QUICK-C、BEAM-C和QA3,设置基准线,并对加速器进行检测和记录,比较各晨检仪的监测结果.依据TG 142报告要求,设置加速器剂量学参数(CAX和SYM)偏差,使用晨检仪检测,测试其灵敏度.结果 4种晨检仪的监测结果与三维水箱和剂量仪测得的基准值相比差异不大,CAX最大偏差为LINA-C的0.5％,FLAT最大偏差为QUICK-C的-0.45％,SYM最大偏差为BEAM-C的0.5％.4台晨检仪均能检测出设定的剂量学参数偏差.结论 各台晨检仪的稳定性均能满足日常检测需求.LINA-C只能提供CAX监测,QUICK-C、BEAM-C和QA3晨检仪除了能够满足AAPM的TG 142报告中的日常设备质量控制的要求,还提供了各自独特的附加功能.基准线的设置是晨检仪是否能准确监测直线加速器剂量学参数的关键因素.测量结果报警时,建议首先检查晨检仪的工作状况,不宜以晨检仪的监测结果直接调整直线加速器.