本工作旨在使用蒙特卡洛代码MCNP5（Monte Carlo N-Particle）对一台Accuray放射治疗仪的辐射束进行建模和表征。这种放疗设备用于在辐射治疗癌症患者时向肿瘤区域提供高剂量的辐射，以杀死癌细胞和缩小肿瘤，然而，如果辐射场不正确，辐射还会损害周围区域和附近的风险器官（OAR）。特别是，具有调强放射治疗（IMRT）的放疗设备可以为患者带来巨大的好处，允许治疗肿瘤区域而不影响周围区域和OAR。现如今，众所周知，在正确模拟放射线在放疗设备中的传输方面可以极大地帮助估算肿瘤、周围区域和OAR的理想剂量。因此，在本工作中，我们使用MCNP5模拟了CECAN的6MV ACCURAY Tomotherapy设备的几何结构。该模型包括一个TomoLINAC，由一个发射具有平均能量为5.7 MeV和宽度为0.3 MeV的高斯分布粒子的电子源组成。发射的粒子撞击钨靶并通过定义等中心辐射场的主要限流器和颚骨。为了验证TomoLINAC中几何结构和辐射传输的精确性，通过调整模拟估算的深度剂量百分比（PDD）曲线和实验测量值来进行了对比。同样，还对比了模拟和实验结果的横向和纵向剖面。此外，通过MCNP对辐射束质量的表征与CECAN的实验数据比较，显示出1%的偏差。在模拟过程中，考虑了放置在水质幻想中的圆柱形探测器，并使用了计数器*F8。对于等中心和SSD（源到表面的距离）为85 cm的场为5×10 cm2的情况，从模拟得到的PDD曲线与实验测量结果之间达到了很好的一致性。同时，对于辐射场为5×40 cm2的情况，在深度为1.5 cm、10 cm和15 cm处获得的模拟和实验横向剖面之间也显示了非常好的一致性。纵向剖面的深度与横向剖面相同，但对于每个剖面，颚骨的开口分别为纵向方向上的5.0 cm、2.5 cm和1.0 cm，对应于病人桌子移动的方向。模拟和实验纵向剖面之间的比较也显示出良好的一致性。对于已经表征过的ACCURAY放疗设备的辐射束，使用Cheese人体模拟器和两个A1SL电离室进行了实验剂量测量。这些实验结果与MCNP估计的结果进行了比较，针对等中心和SAD为85 cm的5×40 cm2场，结论是两者结果在不确定性区域内相似。最后，我们必须强调CECAN的ACCURAY放疗设备的辐射束的建模和表征可以成为不同癌症治疗方案和未来研究中剂量估算的关键工具。版权所有 © 2023 Elsevier Ltd. 保留所有权利。

This work aims to model and characterize the radiation beam of one Accuray tomotherapy equipment using the Monte Carlo Code MCNP5 (Monte Carlo N-Particle). This tomotherapy equipment is used for delivering high doses of radiation in tumor regions to kill cancer cells and shrink the tumor during radiation therapy of cancer patients, however, the radiation can damage surrounding areas and nearby organs at risk (OAR) if the radiation field is not well delimited. In particular, intensity-modulated radiotherapy treatments (IMRT) with tomotherapy equipment offer great benefits to patients allowing treatment of tumor regions without affecting surrounding areas and OAR. Nowadays, it is well known that a correct simulation of transport of radiation in tomotherapy equipment facilitates considerably the estimation of ideal doses in the tumor, surrounding regions, and OAR. For that reason, in this work, we simulated the geometry of the 6 MV ACCURAY Tomotherapy equipment of the CECAN using the MCNP5. The model includes a TomoLINAC consisting of an electron source that emits Gaussian distribution particles with an average energy of 5.7 MeV and width of 0.3 MeV. The emitted particles impact the tungsten target and pass through primary collimators and jaws that define the irradiation field in the isocenter. To validate the geometry and radiation transport in the TomoLINAC the curves of depth dose percentage (PDD) estimated by simulation and the curves measured experimentally were tuned. In the same way, the simulated transverse and longitudinal profiles were compared with the experimental results. In addition, a comparison between the qualities of the radiation beam characterized with MCNP and measured experimentally in CECAN showed a deviation of 1%. For the simulations, cylindrical detectors located inside a water phantom were considered and it was employed the tally *F8. A good agreement was observed between the PDD's curves obtained from the simulation and those measured experimentally for a field of 5 × 10 cm2 in the isocenter and SSD (distance from the source to the surface) of 85 cm. Also, the comparison between the simulated and experimental transverse profiles obtained at 1.5 cm, 10 cm and 15 cm depth with a radiation field of 5 × 40 cm2 showed very good agreement. The longitudinal profiles were estimated with the same depths as the transverse ones, but for each of them, the openings of the jaws were 5.0 cm, 2.5 cm and 1.0 cm in the longitudinal direction, which corresponds to the direction in which the patient's table moves. The comparison between the simulated and experimental longitudinal profiles showed good concordance too. Once the radiation beam of the ACCURAY tomotherapy equipment had been characterized, experimental dose measurements were made using a Cheese phantom and two A1SL ionization chambers. These results obtained experimentally were compared with those estimated with MCNP for a field of 5 × 40 cm2 at the isocenter and SAD of 85 cm and, it was concluded that both results were similar considering the regions of uncertainty. Finally, we must highlight that the modeling and characterization of the radiation beam of CECAN's ACCURAY tomotherapy equipment can be a key tool for dose estimations in different cancer treatment plans and future research.Copyright © 2023 Elsevier Ltd. All rights reserved.