Oxygen-Enhanced R2* Weighted MRI and Diffusion Weighted MRI of Head and Neck Squamous Cell Cancer Lymph Nodes in Prediction of 2-Year Outcome Following Chemoradiotherapy

TL;DR

This study uses MRI to non-invasively assess oxygen levels in lymph nodes of head and neck cancer patients, finding that more hypoxic nodes are less likely to recur after treatment.

Contribution

The study introduces a non-invasive MRI method to assess lymph node hypoxia and its predictive value for treatment outcomes in head and neck cancer.

Findings

Nodes with higher baseline R2* values were more likely to achieve complete response after treatment.

Hypoxic nodes showed increased hypoxia when breathing 100% oxygen and were less likely to recur.

Traditional imaging metrics like node size and DWI were not effective in predicting treatment response.

Abstract

Head and neck squamous cell cancer (HNSCC) with involved lymph nodes (LNs) are often treated with chemoradiotherapy (CRT). Historically, invasive direct measurements showed that LNs can be hypoxic (low in oxygenated blood), and this may be associated with an increased risk of recurrence after CRT. We measured the oxygenation of these LNs non-invasively using MRI (using T2* MR sequences) to test this relationship. We found that, contrary to prior direct measurements, our results suggested that ‘hypoxic’ LNs at baseline tended not to develop recurrence, and furthermore, LNs that became more hypoxic on 100% oxygen were also less likely to develop recurrence.

Background: We evaluated the utility of HNSCC LN R2* relaxation times to infer the oxygenation status of LN non-invasively at baseline and when breathing air and 100% oxygen to predict chemoradiotherapeutic locoregional response at 2 years. Hypoxia within LNs has been associated with poorer outcomes following CRT. Deoxyhaemoglobin decreases MRI transverse relaxation time (T2*) (lengthening inverse, R2*). Methods: A total of 54 patients underwent 1.5T-MRI before CRT. Conventional MR sequences were supplemented with T2* sequences breathing both air and 100% oxygen; pathological nodes identified in consensus were volumetrically contoured to T2* parametric maps. Results: Patients followed-up with for >2 years were categorised by multidisciplinary consensus into post-therapy complete local response (CR; n = 32/54) and local nodal disease relapse (RD; n = 22/54). Our data demonstrated, by R2*, that nodes that sustained post-therapy CR are significantly more hypoxic compared with relapsing nodes and paradoxically demonstrate a significant increase in hypoxia on 100% oxygen. Pre-treatment LN short axis diameter, various qualitative descriptors of malignancy, and quantitative DWI were not useful in discriminating successful response to CRT. Conclusions: This study demonstrates that a significant differential response to 100% oxygen and higher baseline R2* LN measurements could be exploited in risk stratification prior to CRT, and future work could be directed towards understanding the contrast mechanisms of R2* imaging, underpinning the observed differences in the context of hypoxia.

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