Objective: The Monte Carlo (MC) technique can accurately model any linear accelerator where accurate details about the treatment head and the incident electron beam have been provided. However, manufacturers generally do not provide such details as the energy, radial intensity (spot size), or the angular spread of the incident electron beam. The aim of this study is to predict these details and validate a MC Linac model with the measurements.

Methodology: A 10 MV photon beam from an Elekta Synergy Linac was modelled using the BEAMnrc code. The percentage depth dose of the MC model was generated using different electron energies and compared with the measurements using a Gamma index ($\gamma$) with two different criteria sets. The dose profiles of the fine-tuned electron energy were generated using different spot sizes and compared with appropriate measurements. In addition, the fine-tuned electron energy and spot size dose profiles were generated using different angular spreads to minimise any differences. Finally, the output factors for different field sizes, with and without a wedge, and also the quality index, were compared.

Results: The fine-tuned electron energy of the MC model was found to be 9.8 MeV, where 94.12% of the calculation points pass the $\gamma$ test. For the spot size, a circular radial intensity of 0.35 cm best described the 10 MV photon beam. Furthermore, a mean angular spread of 0.05° minimised the cross-field profile differences between calculation and measurement. The largest differences between the output factors from the MC model and measurements were -0.8% and 4.7% for an open and wedged field, respectively. Ultimately, a difference of 0.82% in the quality index was achieved.

Conclusion: A reliable MC model of a 10 MV photon beam Elekta Synergy Linac can be achieved as presented in this study using the BEAMnrc code. This model can be reliably used to calculate dose distributions.

目的：蒙特卡洛（MC）技术可以对任何线性加速器进行精确建模，其中提供了有关治疗头和入射电子束的准确细节。但是，制造商通常不提供诸如能量，径向强度（光斑大小）或入射电子束的角度扩展之类的细节。这项研究的目的是预测这些细节，并通过测量来验证MC Linac模型。

方法：使用BEAMnrc代码对Elekta Synergy Linac的10 MV光子束进行建模。MC模型的百分比深度剂量是使用不同的电子能量生成的，并与使用Gamma指数（$\gamma$）和两个不同的条件集。使用不同的光斑尺寸生成微调电子能量的剂量分布，并将其与适当的测量结果进行比较。另外，使用不同的角展度产生了微调的电子能量和斑点大小的剂量分布，以使任何差异最小化。最后，比较了具有和不具有楔形物的不同场大小的输出因子，以及质量指数。

结果： MC模型的微调电子能量为9.8 MeV，其中94.12％的计算点通过了$\gamma$测试。对于光斑大小，0.35 cm的圆形径向强度最好地描述了10 MV光子束。此外，0.05°的平均角展度将计算和测量之间的交叉场轮廓差异最小化。MC模型的输出因子和测量值之间的最大差异分别是对于开放场和楔入场，分别为-0.8％和4.7％。最终，质量指数相差0.82％。

结论：如本研究中所述，使用BEAMnrc代码可以实现10 MV光子束Elekta Synergy Linac的可靠MC模型。该模型可以可靠地用于计算剂量分布。