Abstract
Diffusion-Weighted Magnetic Resonance imaging (DWI) quantifies water mobility through the Apparent Diffusion Coefficient (ADC), a promising radiotherapy response biomarker. ADC measurements depend on manual delineation of a region of interest, a time-consuming and observer-dependent process. Here, the aim was to introduce and test the performance of a new, semi-automatic delineation tool (SADT) for ADC calculation within the viable region of the tumour. Thirty patients with rectal cancer were scanned with DWI before radiotherapy (RT) (baseline) and two weeks into RT (week 2). The SADT was based on intensities in b=1100smm-2 DWI and derived ADC maps. ADC values measured using the SADT and manual delineations were compared using Bland-Altman- and correlation analyses. Delineations were repeated to assess intra-observer variation, and repeatability was estimated using repeated DWI scans. ADC measured using the SADT and manual delineation showed strong and moderate correlation at baseline and week 2, respectively, with the SADT measuring systematically smaller values. Intra-observer ADC variation was slightly smaller for the SADT compared to manual delineation both at baseline, [-0.00; 0.03] vs. [-0.02; 0.04] 10-3mm2s-1, and week 2, [-0.01; 0.00] vs. [-0.04; 0.07] 10-3mm2s-1 (68.3% limits of agreement). The ADC change between baseline and week 2 was larger than the ADC uncertainty ( 0.04·10-3mm2s-1) in all cases except one. The presented SADT showed performance comparable to manual expert delineation, and with sufficient consistency to allow extraction of potential biological information from the viable tumour.
Highlights
Magnetic Resonance imaging (MRI) is used in radiotherapy (RT) planning as a supplement to computed tomography (CT), primarily because it provides better soft-tissue contrast
We present a simple, semi-automatic tool for delinea tion of the viable tumour volume (VTV), a recommended region of interest (ROI) for Apparent Diffusion Coefficient (ADC) measurement, which is not directly identifiable from raw, high b-value Diffusion-Weighted Magnetic Resonance imaging (DWI) images [18–20]
The observed correlation be tween the semi-automatic delineation tool (SADT) and manual delineation was strong at baseline and moderate at week 2, with the SADT measuring systematically smaller ADC values
Summary
Magnetic Resonance imaging (MRI) is used in radiotherapy (RT) planning as a supplement to computed tomography (CT), primarily because it provides better soft-tissue contrast. Diffusion-Weighted Magnetic Resonance imaging (DWI) quantifies water mobility through the Apparent Diffusion Coefficient (ADC), a promising radiotherapy response biomarker. ADC values measured using the SADT and manual delineations were compared using BlandAltman- and correlation analyses. Results: ADC measured using the SADT and manual delineation showed strong and moderate correlation at baseline and week 2, respectively, with the SADT measuring systematically smaller values. Intra-observer ADC variation was slightly smaller for the SADT compared to manual delineation both at baseline, [− 0.00; 0.03] vs [− 0.02; 0.04] 10− 3 mm s− 1, and week 2, [− 0.01; 0.00] vs [− 0.04; 0.07] 10− 3 mm s− 1 (68.3% limits of agreement). Conclusion: The presented SADT showed performance comparable to manual expert delineation, and with suf ficient consistency to allow extraction of potential biological information from the viable tumour
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