Nuclear Physics Group, EMFTEL and IPARCOS, CEI Moncloa, Universidad Complutense de Madrid, Madrid, Spain.
Instituto de Investigación Sanitaria del Hospital Clínico San Carlos, Madrid, Spain.
Med Phys. 2021 Dec;48(12):8089-8106. doi: 10.1002/mp.15291. Epub 2021 Oct 26.
The INTRABEAM system is a miniature accelerator for low-energy X-ray Intra-Operative Radiation Therapy (IORT), and it could benefit from a fast and accurate dose computation tool. With regards to accuracy, dose computed with Monte Carlo (MC) simulations are the gold standard, however, they require a large computational effort and consequently they are not suitable for real-time dose planning. This work presents a comparison of the implementation on Graphics Processing Unit (GPU) of two different dose calculation algorithms based on MC phase-space (PHSP) information to compute dose distributions for the INTRABEAM device within seconds and with the accuracy of realistic MC simulations.
The MC-based algorithms we present incorporate photoelectric, Compton and Rayleigh effects for the interaction of low-energy X-rays. XIORT-MC (X-ray Intra-Operative Radiation Therapy Monte Carlo) includes two dose calculation algorithms; a Woodcock-based MC algorithm (WC-MC) and a Hybrid MC algorithm (HMC), and it is implemented in CPU and in GPU. Detailed MC simulations have been generated to validate our tool in homogeneous and heterogeneous conditions with all INTRABEAM applicators, including three clinically realistic CT-based simulations. A performance study has been done to determine the acceleration reached with the code, in both CPU and GPU implementations.
Dose distributions were obtained with the HMC and the WC-MC and compared to standard reference MC simulations with more than 95% voxels fulfilling a 7%-0.5 mm gamma evaluation in all the cases considered. The CPU-HMC is 100 times more efficient than the reference MC, and the CPU-WC-MC is about 50 times more efficient. With the GPU implementation, the particle tracking of the WC-MC is faster than the HMC, with the extraction of the particle's information from the PHSP file taking a major part of the time. However, thanks to the variance reduction techniques implemented in the HMC, up to 400 times less particles are needed in the HMC to reach the same level of noise than the WC-MC. Therefore, in our implementation for INTRABEAM energies, the HMC is about 1.3 times more efficient than the WC-MC in an NVIDIA GeForce GTX 1080 Ti card and about 5.5 times more efficient in an NVIDIA GeForce RTX 3090. Dose with noise below 5% has been obtained in realistic situations in less than 5 s with the WC-MC and in less than 0.5 s with the HMC.
The XIORT-MC is a dose computation tool designed to take full advantage of modern GPUs, making possible to obtain MC-grade accurate dose distributions within seconds. Its high speed allows a real-time dose calculation that includes the realistic effects of the beam in voxelized geometries of patients. It can be used as a dose-planning tool in the operating room during a XIORT treatment with any INTRABEAM device.
INTRABEAM 系统是一种用于低能 X 射线术中内放射治疗（IORT）的微型加速器，它可以受益于快速准确的剂量计算工具。在准确性方面，基于蒙特卡罗（MC）模拟计算的剂量是金标准，但是，它们需要大量的计算工作量，因此不适合实时剂量规划。本工作介绍了两种不同的剂量计算算法在图形处理单元（GPU）上的实现，这些算法基于 MC 相空间（PHSP）信息，可在数秒内计算 INTRABEAM 设备的剂量分布，并具有真实 MC 模拟的准确性。
我们提出的基于 MC 的算法包括光电、康普顿和瑞利效应对低能 X 射线的相互作用。XIORT-MC（X 射线术中放射治疗蒙特卡罗）包括两种剂量计算算法；基于 Woodcock 的 MC 算法（WC-MC）和混合 MC 算法（HMC），并在 CPU 和 GPU 上实现。已经进行了详细的 MC 模拟以验证我们在同质和异质条件下的工具，包括所有 INTRABEAM 施源器，包括三个基于临床现实的 CT 模拟。已经进行了性能研究，以确定在 CPU 和 GPU 实现中达到的加速。
使用 HMC 和 WC-MC 获得了剂量分布，并与所有考虑的情况下超过 95%的体素满足 7%-0.5mm 伽马评估的标准 MC 模拟进行了比较。CPU-HMC 的效率比参考 MC 高 100 倍，而 CPU-WC-MC 的效率高 50 倍。在 GPU 实现中，WC-MC 的粒子跟踪速度比 HMC 快，从 PHSP 文件中提取粒子信息占据了大部分时间。然而，由于在 HMC 中实现了方差减少技术，在 HMC 中需要的粒子数减少到 WC-MC 的相同噪声水平的 400 倍以下。因此，在我们针对 INTRABEAM 能量的实现中，在 NVIDIA GeForce GTX 1080 Ti 卡上，HMC 的效率比 WC-MC 高 1.3 倍，在 NVIDIA GeForce RTX 3090 上高 5.5 倍。在 WC-MC 不到 5 秒和 HMC 不到 0.5 秒的时间内，在现实情况下获得了噪声低于 5%的剂量。
XIORT-MC 是一种剂量计算工具，旨在充分利用现代 GPU，可在数秒内获得 MC 级准确的剂量分布。其高速允许在体素化患者几何形状中包括光束的实际效果的实时剂量计算。它可以用作 INTRABEAM 设备进行任何 XIORT 治疗时手术室内的剂量规划工具。
