MRI in head and neck cancer following chemoradiotherapy: what is the optimal delay to demonstrate maximal response?

Abstract

Objectives To investigate the optimal timing for post-chemoradiotherapy (CRT) reference magnetic resonance imaging (MRI) in head and neck cancer, so as to demonstrate a maximal treatment response. To assess whether this differs in human papillomavirus–related oropharyngeal cancer (HPV-OPC) and whether the MRI timing impacts on the ability to predict treatment success. Methods Following ethical approval and informed consent, 45 patients (40 male, mean age 59.7 ± 7.9 years, 33 HPV-OPC) with stage 3 and 4 HNSCC underwent pre-treatment, 6- and 12-week post-CRT MRIs in this prospective cohort study. Primary tumour (n = 39) size, T2w morphology and diffusion weight imaging (DWI) scores, together with nodal (n = 42) size and necrotic/cystic change, were recorded. Interval imaging changes were analysed for all patients and according to HPV-OPC status. MRI descriptors and their interval changes were also compared with 2-year progression-free survival (PFS). Results All MRI descriptors significantly changed between pre-treatment and 6-week post-treatment MRI studies (p < .001). Primary tumour and nodal volume decreased between 6- and 12-week studies; however, interval changes in linear dimensions were only evident for HPV-OPC lymph nodes. Nodal necrosis scores also evolved after 6 weeks but other descriptors were stable. The 6-week nodal necrosis score and the 6- and 12-week nodal volume were predictive of 2-year PFS. Conclusion Apart from HPV-OPC patients with nodal disease, the 6-week post-CRT MRI demonstrates maximal reduction in the linear dimensions of head and neck cancer; however, a later reference study should be considered if volumetric analysis is applied. Key Points • This study provides guidance on when early post-treatment imaging should be performed in head and neck cancer following chemoradiotherapy, in order to aid subsequent detection of recurrent tumour. • Lymph nodes in HPV-related oropharyngeal cancer patients clearly reduced in size from 6 to 12 weeks post-treatment. However, other lymph node disease and all primary tumours showed only a minor reduction in size beyond 6 weeks, and this required a detailed volumetric analysis for demonstration. • Timing of the reference MRI following chemoradiotherapy for head and neck cancer depends on whether the patient has HPV-related oropharyngeal cancer and whether there is nodal disease. MRI as early as 6 weeks post-treatment may be performed unless volumetric analysis is routinely performed.

Imaging of human papilloma virus associated oropharyngeal squamous cell carcinoma and its impact on diagnosis, prognostication, and response assessment

“…In particular, therapy-induced tumour necrosis is thought to lead to an increase in diffusivity and therefore ADC values. 130 Post-CRT increases in ADC metrics following CRT have been associated with disease-free survival in HNSCC; in particular, a rise in post-treatment ADC as well as an increased change in ADC relative to baseline correlated with a favourable prognosis. 97,111,157,158 For example, Connor et al found HNSCC patients with higher post-treatment ADC mean values 6 and 12 weeks following RT were associated with increased 2 year disease free survival rates.…”

“… 127,128 Volume measurements of the primary tumour may also be helpful, with an association between higher post-CRT tumour volumes (both during and 6 weeks after therapy) and local failure. 129 Relative to CT, MRI is particularly helpful in this situation, given its superior ability to differentiate between tumour and peritumoral oedema 130 Both CT and MRI may be used to evaluate post-treatment changes in nodal volume, with greater percentage reductions associated with treatment success. 127,128 …”

“…In view of this, earlier post-CRT MRI may be appropriate for HPV- OPC, but 12 week scanning remains appropriate for HPV+ cases with nodal disease. 130 …”