Vanstalle Marie, Constanzo Julie, Karakaya Yusuf, Finck Christian, Rousseau Marc, Brasse David
Université de Strasbourg, CNRS, IPHC UMR 7178, Strasbourg, F-67000, France.
Med Phys. 2018 Jan;45(1):470-478. doi: 10.1002/mp.12696. Epub 2017 Dec 15.
Due to the considerable development of proton radiotherapy, several proton platforms have emerged to irradiate small animals in order to study the biological effectiveness of proton radiation. A dedicated analytical treatment planning tool was developed in this study to accurately calculate the delivered dose given the specific constraints imposed by the small dimensions of the irradiated areas.
The treatment planning system (TPS) developed in this study is based on an analytical formulation of the Bragg peak and uses experimental range values of protons. The method was validated after comparison with experimental data from the literature and then compared to Monte Carlo simulations conducted using Geant4. Three examples of treatment planning, performed with phantoms made of water targets and bone-slab insert, were generated with the analytical formulation and Geant4. Each treatment planning was evaluated using dose-volume histograms and gamma index maps.
We demonstrate the value of the analytical function for mouse irradiation, which requires a targeting accuracy of 0.1 mm. Using the appropriate database, the analytical modeling limits the errors caused by misestimating the stopping power. For example, 99% of a 1-mm tumor irradiated with a 24-MeV beam receives the prescribed dose. The analytical dose deviations from the prescribed dose remain within the dose tolerances stated by report 62 of the International Commission on Radiation Units and Measurements for all tested configurations. In addition, the gamma index maps show that the highly constrained targeting accuracy of 0.1 mm for mouse irradiation leads to a significant disagreement between Geant4 and the reference. This simulated treatment planning is nevertheless compatible with a targeting accuracy exceeding 0.2 mm, corresponding to rat and rabbit irradiations.
Good dose accuracy for millimetric tumors is achieved with the analytical calculation used in this work. These volume sizes are typical in mouse models for radiation studies. Our results demonstrate that the choice of analytical rather than simulated treatment planning depends on the animal model under consideration.
由于质子放疗的显著发展，出现了几种用于辐照小动物的质子平台，以研究质子辐射的生物学效应。在本研究中开发了一种专用的分析治疗计划工具，以在考虑到辐照区域尺寸小所带来的特定限制的情况下，准确计算所输送的剂量。
本研究中开发的治疗计划系统（TPS）基于布拉格峰的解析公式，并使用质子的实验射程值。该方法在与文献中的实验数据进行比较后得到验证，然后与使用Geant4进行的蒙特卡罗模拟进行比较。使用由水靶和骨板插件制成的模体进行了三个治疗计划示例，分别用解析公式和Geant4生成。每个治疗计划都使用剂量体积直方图和伽马指数图进行评估。
我们证明了用于小鼠辐照的解析函数的价值，这需要0.1毫米的靶向精度。使用适当的数据库，解析模型限制了因错误估计阻止本领而导致的误差。例如，用24兆电子伏的束流辐照1毫米的肿瘤，99%的肿瘤接受了规定剂量。对于所有测试配置，解析剂量与规定剂量的偏差均保持在国际辐射单位与测量委员会第62号报告所述的剂量容差范围内。此外，伽马指数图显示，小鼠辐照所需的0.1毫米的高度受限靶向精度导致Geant4与参考值之间存在显著差异。然而，这种模拟治疗计划与超过0.2毫米的靶向精度兼容，这对应于大鼠和兔子的辐照。
本工作中使用的解析计算实现了对毫米级肿瘤的良好剂量精度。这些体积大小在辐射研究的小鼠模型中很典型。我们的结果表明，选择解析治疗计划而非模拟治疗计划取决于所考虑的动物模型。
