Diffusion-weighted MRI to assess response to chemoradiotherapy in rectal cancer: main interpretation pitfalls and their use for teaching
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To establish the most common image interpretation pitfalls for non-expert readers using diffusion-weighted imaging (DWI) to assess response to chemoradiotherapy in patients with rectal cancer and to explore the use of these pitfalls in an expert teaching setting.
Two independent non-expert readers (R1 and R2) scored the restaging DW MRI scans (b1,000 DWI, in conjunction with ADC maps and T2-W MRI scans for anatomical reference) in 100 patients for the likelihood of a complete response versus residual tumour using a five-point confidence score. The readers received expert feedback and the final response outcome for each case. The supervising expert documented any potential interpretation errors/pitfalls discussed for each case to identify the most common pitfalls.
The most common pitfalls were the interpretation of low signal on the ADC map, small susceptibility artefacts, T2 shine-through effects, suboptimal sequence angulation and collapsed rectal wall. Diagnostic performance (area under the ROC curve) was 0.78 (R1) and 0.77 (R2) in the first 50 patients and 0.85 (R1) and 0.85 (R2) in the final 50 patients.
Five main image interpretation pitfalls were identified and used for teaching and feedback. Both readers achieved a good diagnostic performance with an AUC of 0.85.
• Fibrosis appears hypointense on an ADC map and should not be mistaken for tumour.
• Susceptibility artefacts on rectal DWI are an important potential pitfall.
• T2 shine-through on rectal DWI is an important potential pitfall.
• These pitfalls are useful to teach non-experts how to interpret rectal DWI.
KeywordsRectal neoplasms Chemoradiotherapy Magnetic resonance imaging Diffusion magnetic resonance imaging Diagnosis
Compliance with ethical standards
The scientific guarantor of this publication is Doenja Lambregts.
Conflict of interest
The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
The authors state that this work did not receive any funding.
Statistics and biometry
No complex statistical methods were necessary for this paper.
Institutional Review Board approval was obtained.
Written informed consent was waived by the Institutional Review Board.
Overlap of study subjects or cohorts
Some of the study patients were included in previously reported studies, as follows:
- The following study included the 38 patients with a clinical complete response after CRT with follow-up according to a watchful waiting strategy:
Martens MH, et al. Long-term outcome of an organ preservation program after neoadjuvant treatment for rectal cancer. J Natl Cancer Inst. 2016;108(12).
This study reports the clinical outcomes in these patients and did not focus on imaging.
Studies on diffusion-weighted imaging
- The following study included one of the patients in our study:
Curvo-Semedo L, et al. Rectal cancer: assessment of complete response to preoperative combined radiation therapy with chemotherapy – conventional MR volumetry versus diffusion-weighted MR imaging. Radiology. 2011;260(3):734–43.
This study focused on quantitative (ADC and volume) measurements and not on visual assessment of DWI.
- The following study included 15 of the patients in our study:
Lambregts DM, et al. MRI and diffusion-weighted MRI volumetry for identification of complete tunour responders after preoperative chemoradiotherapy in patients with rectal cancer: a bi-institutional validation study. Ann Surg. 2015;262(6):1034–9.
This study focused on quantitative (volume) measurements on DWI. It did not include visual DWI assessment, pitfalls or teaching effects.
- The following study included 12 of the patients in our study:
van Heeswijk MM, et al. Automated and semiautomated segmentation of rectal tunour volumes on diffusion-weighted MRI: can it replace manual volumetry? Int J Radiat Oncol Biol Phys. 2016;94(4):824–31.
This study was a technical study on automated software methods to measure tumour volumes on DWI. It did not include a visual assessment or comparison of DWI findings with treatment response.
- The following study included 21 of the patients in our study:
van Heeswijk MM, et al. DWI for assessment of rectal cancer nodes after chemoradiotherapy: is the absence of nodes on DWI proof of a negative nodal status? AJR Am J Roentgenol. 2017;208(3):W79–W84.
This study focused on DWI for lymph node assessment and not for tumour response evaluation.
• Diagnostic or prognostic study
• Performed at one institution
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- 22.Martens M, Maas M, Heijnen LA et al (2016) Long term outcome of an organ preservation program after neoadjuvant treatment for rectal cancer. J Natl Cancer Inst 108(12). doi: 10.1093/jnci/djw171