Fernando Nitara, Tadic Tony, Li Winnie, Patel Tirth, Padayachee Jerusha, Santiago Anna T, Dang Jennifer, Chung Peter, Gutierrez Enrique, Coolens Catherine, Taylor Edward, Winter Jeff D
Medical Biophysics, Western University, London, Ontario, Canada.
Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada.
Phys Imaging Radiat Oncol. 2024 Mar 15;30:100570. doi: 10.1016/j.phro.2024.100570. eCollection 2024 Apr.
Integrated magnetic resonance linear accelerator (MR-Linac) systems offer potential for biologically based adaptive radiation therapy using apparent diffusion coefficient (ADC). Accurate tracking of longitudinal ADC changes is key to establishing ADC-driven dose adaptation. Here, we report repeatability and reproducibility of intraprostatic ADC using deformable image registration (DIR) to correct for inter-fraction prostate changes.
The study included within-fraction repeat ADC measurements for three consecutive fractions for 20 patients with prostate cancer treated on a 1.5 T MR-Linac. We deformably registered successive fraction T-weighted images and applied the deformation vector field to corresponding ADC maps to align to fraction 2. We delineated gross tumour volume (GTV), peripheral zone (PZ) and prostate clinical target volume (CTV) regions-of-interest (ROIs) on T-weighted MRI and copied to ADC maps. We computed intraclass correlation coefficients (ICC) and percent repeatability coefficient (%RC) to determine within-fraction repeatability and between-fraction reproducibility for individual voxels, mean and 10th percentile ADC values per ROI.
The ICC between repeats and fractions was excellent for mean and 10th percentile ADC in all ROIs (ICC > 0.86), and moderate repeatability and reproducibility existed for individual voxels (ICC > 0.542). Similarly, low %RC within-fraction (4.2-17.9 %) mean and 10th percentile ADC existed, with greater %RC between fractions (10.2-36.8 %). Higher %RC existed for individual voxel within-fraction (21.7-30.6 %) and between-fraction (32.1-34.5 %) ADC.
Results suggest excellent ADC repeatability and reproducibility in clinically relevant ROIs using DIR to correct between-fraction anatomical changes. We established the precision of voxel-level ADC tracking for future biologically based adaptation implementation.
集成磁共振直线加速器（MR-Linac）系统为基于表观扩散系数（ADC）的生物适应性放射治疗提供了可能。准确跟踪纵向ADC变化是建立ADC驱动的剂量适应性的关键。在此，我们报告使用可变形图像配准（DIR）校正分次间前列腺变化后前列腺内ADC的重复性和再现性。
本研究纳入了20例在1.5T MR-Linac上接受治疗的前列腺癌患者，对其连续三个分次进行分次内重复ADC测量。我们对连续分次的T加权图像进行可变形配准，并将变形矢量场应用于相应的ADC图，使其与第二个分次对齐。我们在T加权MRI上勾勒出大体肿瘤体积（GTV）、外周带（PZ）和前列腺临床靶体积（CTV）感兴趣区（ROI），并复制到ADC图上。我们计算组内相关系数（ICC）和百分重复性系数（%RC），以确定每个体素、每个ROI的平均ADC值和第10百分位数ADC值的分次内重复性和分次间再现性。
所有ROI中，平均ADC值和第10百分位数ADC值在重复测量和分次间的ICC均极佳（ICC>0.86），个体体素的重复性和再现性中等（ICC>0.542）。同样，分次内平均ADC值和第10百分位数ADC值的%RC较低（4.2-17.9%），分次间的%RC较高（10.2-36.8%）。个体体素分次内（21.7-30.6%）和分次间（32.1-34.5%）ADC的%RC更高。
结果表明，使用DIR校正分次间解剖变化后，临床相关ROI中的ADC具有出色的重复性和再现性。我们建立了体素级ADC跟踪的精度，以便未来实施基于生物学的适应性放疗。
