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The primary aim of ACRIN 6698 was the evaluation of breast diffusion weighted imaging (DWI) for the prediction of response to neoadjuvant chemotherapy (NAC) for invasive breast cancer. For this purpose, serial MRI studies were acquired over the course of treatment. The study schema for the ACRIN 6698 Trial is shown in Figure 1.
MRI studies were performed at up to four time points in the course of NAC:
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- T2-weighted sequence
- DWI (b=0, 100, 600, 800 s/mm2, 3-direction)
- T1-weighted DCE (Dynamic Contrast Enhanced) (80sec < phase duration < 100sec; > 8 minutes continuous post-injection acquisition)
Protocol limits on scan parameters for these required acquisitions are given in an accompanying document (see final section on this page).
All required imaging was performed axially (looking down through the body) with full bilaterally coverage. For the TCIA collection all original images from these three acquisitions are included. Derived images (an image whose pixel values have been derived in some manner from the pixel value of one or more other images) including reformats, CAD software outputs and MIP images are not part of the collection. For the T2w acquisitions multiple series are included if they were generated as part of the standard reconstruction process on the scanner. For example, acquisitions utilizing Dixon techniques to create separate fat and water images will have multiple series in the collection. All original DWI series are included, including directional diffusion images if they were stored with the study. For some General Electric (GEMS) scanners employed in the trial the acquisition software allowed only 2 b-values in a single DWI acquisition. For studies on these scanners the multiple b-value protocol DWI consisted of three consecutive two b-value series ([0,800], [0,600] and [0,100] s/mm2). A separate “merged series multi-b” (MSMB) series containing all b>0 images from the three series plus a single b=0 s/mm2 image created by averaging the three acquired b=0 images was created for analysis and is included in the collection. The DICOM metadata fields in the MSMB series have been set to permit reading as a standard GEMS multi-b acquisition. During automated QC procedures, the MSMB series were rejected if any sequence related parameters other than the b value differed between the multiple two b-value acquisitions. The original 2-b acquisition series are also included in the collection.
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The segmentations provided in the derived diffusion objects are those generated for and used in the primary analysis and test/retest analyses for the ACRIN-6698 study. Tumor was identified on post-contrast DCE subtraction images and then localized on the ADC map. (apparent diffusion coefficient) Multi-slice, whole-tumor regions of interest (ROIs) were manually defined by selecting regions with low ADC and hyperintensity on a high b-value DWI (b=600 or 800 s/mm2) while avoiding adjacent adipose and fibroglandular tissue, biopsy clip artifacts, and regions of high T2 signal (e.g., seroma and necrosis). For multicentric/multifocal disease, all disease regions were included in the ROI. Region definition was done at the UCSF processing lab using in-house software tools developed with IDL (Exelis Visual Information Solutions, Boulder, Colorado).
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Figure 2 shows the enrollment numbers and exclusions used to determine the analysis cohort for the primary analysis. For this TCIA collection we include MRI studies from 385 of the 388 eligible subjects, three being excluded due to having no analyzable MRI studies received by the central imaging lab. The 116 patients excluded from the primary analysis as “Not Randomized” were those screened out of I‑SPY 2, most commonly due to being in the low-risk category (HR+/HER2- subtype with low MammaPrint score). Note that all these patients have baseline MRI studies included in this collection, and some were included in the ACRIN-6698 test/retest repeatability arm. A separate TCIA download option is provided for researchers who wish to focus on the 242-patient cohort used in the primary analysis. These subjects all had MRI studies with DWI scans that passed the QC evaluations at baseline and at least one later time point. One other download option is provided for the 71-patient cohort with analyzable test/retest. The primary aim and test/retest studies are the only ones guaranteed to have tumor segmentations and DWI derived objects in this collection.
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