Département de Radio-Oncologie et Centre de Recherche en Cancérologie de l'Université Laval, Hôtel-Dieu de Québec, Québec, QC, Canada.
Int J Radiat Oncol Biol Phys. 2011 Dec 1;81(5):1582-9. doi: 10.1016/j.ijrobp.2010.09.029. Epub 2010 Nov 13.
Brachytherapy planning software relies on the Task Group report 43 dosimetry formalism. This formalism, based on a water approximation, neglects various heterogeneous materials present during treatment. Various studies have suggested that these heterogeneities should be taken into account to improve the treatment quality. The present study sought to demonstrate the feasibility of incorporating Monte Carlo (MC) dosimetry within an inverse planning algorithm to improve the dose conformity and increase the treatment quality.
The method was based on precalculated dose kernels in full patient geometries, representing the dose distribution of a brachytherapy source at a single dwell position using MC simulations and the Geant4 toolkit. These dose kernels are used by the inverse planning by simulated annealing tool to produce a fast MC-based plan. A test was performed for an interstitial brachytherapy breast treatment using two different high-dose-rate brachytherapy sources: the microSelectron iridium-192 source and the electronic brachytherapy source Axxent operating at 50 kVp.
A research version of the inverse planning by simulated annealing algorithm was combined with MC to provide a method to fully account for the heterogeneities in dose optimization, using the MC method. The effect of the water approximation was found to depend on photon energy, with greater dose attenuation for the lower energies of the Axxent source compared with iridium-192. For the latter, an underdosage of 5.1% for the dose received by 90% of the clinical target volume was found.
A new method to optimize afterloading brachytherapy plans that uses MC dosimetric information was developed. Including computed tomography-based information in MC dosimetry in the inverse planning process was shown to take into account the full range of scatter and heterogeneity conditions. This led to significant dose differences compared with the Task Group report 43 approach for the Axxent source.
近距离治疗计划软件依赖于 TG-43 剂量学形式。该形式基于水近似，忽略了治疗过程中存在的各种异质材料。多项研究表明，应考虑这些异质性以提高治疗质量。本研究旨在证明在反演规划算法中纳入蒙特卡罗（MC）剂量学以改善剂量适形性和提高治疗质量的可行性。
该方法基于全患者几何形状的预计算剂量核，代表使用 MC 模拟和 Geant4 工具包在单个驻留位置的近距离治疗源的剂量分布。这些剂量核由模拟退火反向规划工具用于生成快速基于 MC 的计划。使用两种不同的高剂量率近距离治疗源：微选择铱-192 源和电子近距离治疗源 Axxent（工作在 50 kVp），对乳腺间质近距离治疗进行了测试。
将模拟退火反向规划的研究版本与 MC 结合，使用 MC 方法为充分考虑剂量优化中的异质性提供了一种方法。发现水近似的影响取决于光子能量，与铱-192 相比，Axxent 源的较低能量导致更大的剂量衰减。对于后者，发现 90%的临床靶体积接受的剂量有 5.1%的剂量不足。
开发了一种新的优化后装近距离治疗计划的方法，该方法使用 MC 剂量学信息。在反演规划过程中，将基于 CT 的信息纳入 MC 剂量学中，表明可以考虑散射和异质性条件的全部范围。与 Axxent 源的 TG-43 方法相比，这导致了显著的剂量差异。
