Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan, 81746-73441, Iran.
Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 55455, USA.
Med Phys. 2019 Nov;46(11):5273-5283. doi: 10.1002/mp.13796. Epub 2019 Sep 28.
To evaluate the effect of beam configuration with inaccurate or incomplete small field output factors on the accuracy of dose calculations in treatment planning systems.
Output factors were measured using various detectors and for a range of field sizes. Three types of treatment machines were configured in two treatment planning systems. In the first (corrected) machine, the Exradin W1 scintillator was used to determine output factors. In the second (uncorrected) machine, the measured output factors by the A1SL ion chamber without considering output correction factors for small field sizes were utilized. In the third (clinical) machine, measured output factors by the Exradin W1 were used but not for field sizes smaller than 2 × 2 cm . The dose computed by the anisotropic analytical algorithm (AAA), Acuros XB (AXB) and collapsed cone convolution/superposition (CCC) algorithms in the three machines were delivered using static (jaw-, MLC-, and jaw/MLC-defined), and composite [intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT)] fields. The differences between measured and calculated dose values were analyzed.
For static fields, the percentage differences between measured and calculated doses by the three algorithms in three configured machines were <2% for field sizes larger than 2 × 2 cm . In jaw- and jaw/MLC-defined fields smaller than 2 × 2 cm , the corrected machine presented better agreement with measurement. Considering output correction factors in MLC-defined fields, among the three configured machines, the accuracy of calculation improved to within ±0.5%. For MLC-defined field size of 1 × 1 cm , AXB showed the smallest percentage difference (1%). In IMRT and VMAT plans, the percentage differences between measured and calculated doses at the isocenter, as well as the gamma analysis of different plans, which include field sizes larger than 3 × 3 cm , did not vary noticeably. For smaller field sizes, using the corrected machine influences dose calculation accuracy.
Configuration with corrected output factors improves accuracy of dose calculation for static field sizes smaller than 2 × 2 cm . For very small fields, the robustness of the dose calculation algorithm affects the accuracy of dose as well. In IMRT and VMAT plans, which include small subfields, the size of the jaw-defined field is an important factor and using corrected output factors increases dose calculation accuracy.
评估在治疗计划系统中，不准确或不完整的小射野输出因子对剂量计算准确性的影响。
使用各种探测器和一系列射野大小测量输出因子。在两种治疗计划系统中配置了三种治疗机。在第一台（校正）机器中，使用 Exradin W1 闪烁体来确定输出因子。在第二台（未校正）机器中，使用 A1SL 离子室测量输出因子，但不考虑小射野大小的输出校正因子。在第三台（临床）机器中，使用 Exradin W1 测量输出因子，但不用于小于 2×2cm 的射野。在这三种机器中，各使用各向异性分析算法（AAA）、Acuros XB（AXB）和锥形束卷积/叠加（CCC）算法计算剂量。使用静态（准直器、多叶准直器和准直器/多叶准直器定义）和复合（调强放疗（IMRT）、容积调强弧形治疗（VMAT））射野输送由这三种算法计算的剂量。分析测量和计算剂量值之间的差异。
对于静态射野，在三种配置机器中，对于大于 2×2cm 的射野，三种算法的测量和计算剂量之间的百分比差异<2%。在小于 2×2cm 的准直器和准直器/多叶准直器定义的射野中，校正后的机器与测量结果更吻合。在多叶准直器定义的射野中考虑输出校正因子，在三种配置机器中，计算精度提高到±0.5%。对于 1×1cm 的多叶准直器定义的射野，AXB 显示最小的百分比差异（1%）。在 IMRT 和 VMAT 计划中，在等中心处测量和计算剂量之间的百分比差异，以及包括大于 3×3cm 的射野的不同计划的伽马分析，没有明显变化。对于较小的射野，使用校正后的机器会影响剂量计算的准确性。
对于小于 2×2cm 的静态射野，使用校正后的输出因子可以提高剂量计算的准确性。对于非常小的射野，剂量计算算法的稳健性也会影响剂量的准确性。在包括小子野的 IMRT 和 VMAT 计划中，准直器定义的射野大小是一个重要因素，使用校正后的输出因子可以提高剂量计算的准确性。
