Keivan Hadi, Shahbazi-Gahrouei Daryoush, Shanei Ahmad, Amouheidari Alireza
Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
Department of Radiation Oncology, Isfahan Milad Hospital, Isfahan, Iran.
J Med Signals Sens. 2018 Jan-Mar;8(1):39-45.
Dosimetric accuracy in intensity-modulated radiation therapy (IMRT) is the main part of quality assurance program. Improper beam modeling of small fields by treatment planning system (TPS) can lead to inaccuracy in treatment delivery. This study aimed to evaluate of the dose delivery accuracy at small segments of IMRT technique using two-dimensional (2D) array as well as evaluate the capability of two TPSs algorithm in modeling of small fields.
Irradiation were performed using 6 MV photon beam of Siemens Artiste linear accelerator. Dosimetric behaviors of two dose calculation algorithms, namely, collapsed cone convolution/superposition (CCCS) and full scatter convolution (FSC) in small segments of IMRT plans were analyzed using a 2D diode array and gamma evaluation.
Comparisons of measurements against TPSs calculations showed that percentage difference of output factors of small fields were 2% and 15% for CCCS and FSC algorithm, respectively. Gamma analysis of calculated dose distributions by TPSs against those measured by 2D array showed that in passing criteria of 3 mm/3%, the mean pass rate for all segment sizes is higher than 95% except for segment sizes below 3 cm × 3 cm optimized by TiGRT TPS.
High pass rate of gamma index (95%) achieved in planned small segments by Prowess relative to results obtained with TiGRT. This study showed that the accuracy of small field modeling differs between two dose calculation algorithms.
调强放射治疗（IMRT）中的剂量测定准确性是质量保证计划的主要部分。治疗计划系统（TPS）对小射野的射束建模不当会导致治疗实施不准确。本研究旨在使用二维（2D）阵列评估IMRT技术小射野的剂量传递准确性，并评估两种TPS算法对小射野建模的能力。
使用西门子Artiste直线加速器的6 MV光子束进行照射。使用2D二极管阵列和伽马评估分析IMRT计划小射野中两种剂量计算算法（即坍缩卷积/叠加法（CCCS）和全散射卷积法（FSC））的剂量学行为。
测量值与TPS计算值的比较表明，对于CCCS和FSC算法，小射野输出因子的百分比差异分别为2%和15%。TPS计算的剂量分布与2D阵列测量的剂量分布的伽马分析表明，在3 mm/3%的通过标准下，除了TiGRT TPS优化的3 cm×3 cm以下的射野尺寸外，所有射野尺寸的平均通过率均高于95%。
相对于TiGRT获得的结果，Prowess在计划的小射野中实现了较高的伽马指数通过率（95%）。本研究表明，两种剂量计算算法在小射野建模的准确性上存在差异。
