Dynamic Contrast-enhanced and Diffusion-weighted Magnetic Resonance Imaging for Response Evaluation After Single-Dose Ablative Neoadjuvant Partial Breast Irradiation

Abstract

Purpose: We aimed to evaluate changes in dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance imaging (MRI) scans acquired before and after single-dose ablative neoadjuvant partial breast irradiation (NA-PBI), and explore the relation between semiquantitative MRI parameters and radiologic and pathologic responses.

Methods and materials: We analyzed 3.0T DCE and DW-MRI of 36 patients with low-risk breast cancer who were treated with single-dose NA-PBI, followed by breast-conserving surgery 6 or 8 months later. MRI was acquired before NA-PBI and 1 week, 2, 4, and 6 months after NA-PBI. Breast radiologists assessed the radiologic response and breast pathologists scored the pathologic response after surgery. Patients were grouped as either pathologic responders or nonresponders (<10% vs ≥10% residual tumor cells). The semiquantitative MRI parameters evaluated were time to enhancement (TTE), 1-minute relative enhancement (RE_1min), percentage of enhancing voxels (%EV), distribution of washout curve types, and apparent diffusion coefficient (ADC).

Results: In general, the enhancement increased 1 week after NA-PBI (baseline vs 1 week median - TTE: 15s vs 10s; RE_1min: 161% vs 197%; %EV: 47% vs 67%) and decreased from 2 months onward (6 months median - TTE: 25s; RE_1min: 86%; %EV: 12%). Median ADC increased from 0.83 × 10^-3 mm²/s at baseline to 1.28 × 10^-3 mm²/s at 6 months. TTE, RE_1min, and %EV showed the most potential to differentiate between radiologic responses, and TTE, RE_1min, and ADC between pathologic responses.

Conclusions: Semiquantitative analyses of DCE and DW-MRI showed changes in relative enhancement and ADC 1 week after NA-PBI, indicating acute inflammation, followed by changes indicating tumor regression from 2 to 6 months after radiation therapy. A relation between the MRI parameters and radiologic and pathologic responses could not be proven in this exploratory study.

Fig. 1

High-temporal (gray boxes) and high-spatial (blue boxes) dynamic contrast-enhanced-magnetic resonance imaging acquisition showing: median relative enhancement (RE) in aorta region of interest (orange) and 90th percentile RE in gross tumor volume-region of interest in the high-temporal (gray) and high-spatial dynamic contrast-enhanced (blue) series. The vertical dashed lines indicate the onset of aorta enhancement (left) and gross tumor volume enhancement (right). Indicated semiquantitative parameters are time to enhancement (TTE), 1-minute relative enhancement (RE_1min), and cutoff boundaries (–10% and +10% RE) for voxel-wise washout curve type classification.

Fig. 2

Overview of all magnetic resonance images acquired in a single patient and gross tumor volume-regions of interest used for analysis (yellow). The high-spatial dynamic contrast-enhanced magnetic resonance imaging (MRI) insets show the washout curve types for the voxels >100% relative enhancement: Type 1 (blue), type 2 (green), and type 3 (red). This patient had no radiologic complete response at any moment and showed a near pathologic complete response (<10% residual tumor cells) after surgery.

Fig. 3

Median (interquartile range) semiquantitative parameter values before and after neoadjuvant partial breast irradiation, grouped by qualitative radiologic response along with the number of available scans per scan moment.

Fig. 4

Median (interquartile range) semiquantitative parameter values before and after neoadjuvant partial breast irradiation, grouped by pathologic response along with the number of available scans per scan moment.