Ghiasi Hosein, Mesbahi Asghar
Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran.
Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran ; Radiation Oncology Department, Imam Hospital, Tabriz, Iran.
Rep Pract Oncol Radiother. 2012 May 24;17(4):220-5. doi: 10.1016/j.rpor.2012.03.011. eCollection 2012.
Photoneutrons are produced in radiation therapy with high energy photons. Also, capture gamma rays are the byproduct of neutrons interactions with wall material of radiotherapy rooms.
In the current study an analytical formula was proposed for capture gamma dose calculations in double bend mazes in radiation therapy rooms.
A total of 40 different layouts with double-bend mazes and a 18 MeV photon beam of Varian 2100 Clinac were simulated using MCNPX Monte Carlo (MC) code. Neutron capture gamma ray dose equivalent was calculated by the MC method along the maze and at the maze entrance door of all the simulated rooms. Then, all MC resulted data were fitted to an empirical formula for capture gamma dose calculations. Wu-McGinley analytical formula for capture gamma dose equivalent at the maze entrance door in single-bend mazes was also used for comparison purposes.
For capture gamma dose equivalents at the maze entrance door, the difference of 2-11% was seen between MC and the derived equation, while the difference of 36-87% was found between MC and the Wu-McGinley methods.
Our results showed that the derived formula results were consistent with the MC results for all of 40 different geometries. However, as a new formula, further evaluations are required to validate its use in practical situations. Finally, its application is recommend for capture gamma dose calculations in double-bend mazes to improve shielding calculations.
在高能光子放射治疗中会产生光中子。此外，俘获γ射线是中子与放射治疗室墙壁材料相互作用的副产品。
在本研究中，提出了一种用于计算放射治疗室双弯迷路俘获γ剂量的解析公式。
使用MCNPX蒙特卡罗（MC）代码模拟了40种不同布局的双弯迷路以及Varian 2100直线加速器的18 MeV光子束。通过MC方法计算了所有模拟房间沿迷路以及迷路入口处的中子俘获γ射线剂量当量。然后，将所有MC结果数据拟合为一个用于俘获γ剂量计算的经验公式。还使用了单弯迷路中迷路入口处俘获γ剂量当量的Wu-McGinley解析公式进行比较。
对于迷路入口处的俘获γ剂量当量，MC与推导公式之间的差异为2% - 11%，而MC与Wu-McGinley方法之间的差异为36% - 87%。
我们的结果表明，对于所有40种不同几何形状，推导公式的结果与MC结果一致。然而，作为一个新公式，需要进一步评估以验证其在实际情况中的应用。最后，建议将其应用于双弯迷路的俘获γ剂量计算，以改进屏蔽计算。
