The Effects of Human Papillomavirus Status and Treatment on the Positive Predictive Value of Post-radiotherapy 18F-Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography in Advanced Head and Neck Squamous Cell Carcinoma

AIMS

The high negative predictive value of post-chemoradiation (CRT) positron emission tomography-computed tomography (PET-CT) is well established in head and neck squamous cell cancers (HNSCC). The positive predictive value (PPV) remains under scrutiny, with increasing evidence that it is affected by several factors. The aim of this study was to assess the PPV of post-treatment PET-CT for residual nodal disease when stratified by treatment modality and tumour human papillomavirus (HPV) status.

MATERIALS AND METHODS

This was a retrospective cohort study in a tertiary oncology centre carried out between January 2013 and December 2019. Patients were radically treated with radiotherapy only/CRT for node-positive HNSCC. PET-CT nodal responses were categorised as complete, equivocal (EQR) or incomplete (ICR), and outcomes extracted from electronic records.

RESULTS

In total, 480 patients were evaluated, all had a minimum potential follow-up of 2 years, with a median of 39.2 months. The PPV of 12-week PET-CT was significantly different between HPV-positive (22.5%) and HPV-unrelated (52.7%) disease, P < 0.001. It was also significantly different between the CRT (24.8%) and radiotherapy-only (51.1%) groups, P = 0.001. The PPV of an EQR was significantly less than an ICR, irrespective of HPV status and primary treatment modality. In HPV-positive disease, the PPV of an EQR was 9.0% for the CRT group compared with 21.4% for radiotherapy only, P = 0.278. The PPV in those who achieved an ICR was 34.2% in the CRT group, significantly lower than 70.0% in the radiotherapy-only group, P = 0.03.

CONCLUSION

The PPV of 12-week PET-CT is significantly lower for HPV-positive compared with HPV-unrelated HNSCC. It is poorer in patients with HPV-positive disease treated with CRT compared with radiotherapy alone.

Positron Emission Tomography-Computed Tomography Surveillance after (Chemo)Radiotherapy in Advanced Head and Neck Squamous Cell Cancer: Beyond the PET-NECK Protocol

AIMS

To evaluate the implementation of 18-fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) surveillance after (chemo)radiotherapy, to compare outcomes for those who achieved a complete (CR), equivocal (EQR) and incomplete (ICR) nodal response on 12-week PET-CT according to their human papillomavirus (HPV) status, and to assess the safety of ongoing surveillance beyond 12 weeks in the HPV-positive EQR group.

MATERIALS AND METHODS

All patients with node-positive head and neck squamous cell carcinoma (HNSCC) treated with (chemo)radiotherapy between January 2013 and September 2017 were identified. PET-CT responses were classified as CR, ICR or EQR. Patient outcomes were obtained from electronic records.

RESULTS

In total, 236 patients with a minimum of 2 years of follow-up were identified. The mean age was 59 years; 79.3% had N2 disease; 77.1% of patients had oropharyngeal cancer and 10.1% had squamous cell carcinoma of unknown primary, of whom 82.0% (169) were HPV positive; 78.0% received chemoradiotherapy. The median time from the end of radiotherapy to PET-CT was 91 days. Of the HPV-related HNSCC, 60.4% achieved CR, 29.0% EQR and 10.6% ICR. With a median follow-up of 41.7 months, there was no difference in survival between patients with HPV-related HNSCC achieving CR and EQR (median overall survival not reached for both, P = 0.67) despite the omission of immediate neck dissection in 98.0% of the EQR group.

CONCLUSION

Patients with HPV-positive HNSCC who have achieved EQR have comparable survival outcomes to those who achieved a CR despite the omission of immediate neck dissections; this shows the safety of ongoing surveillance beyond 12 weeks in this group of patients.

Thermal injuries associated with MRI

Most physicians are aware of the absolute contraindications to magnetic resonance imaging (MRI). However, less familiar is the potential for an MRI-induced thermal or electrical burn associated with electrical monitoring devices. Although detailed studies concerning the burn hazard in MRI have not been reported, it is widely believed that direct electromagnetic induction in looped cables associated with the patient is responsible for the excessive heating and it is on this theory that present guidelines are based. Recent reports have however indicated that other mechanisms may cause the heating of metal, either in or on the patient. This document reviews numerous reported burn injuries sustained during MRI and addresses the underlying heating mechanisms possibly causing these events.

Investigation of the factors responsible for burns during MRI

Numerous reported burn injuries have been sustained during clinical MRI procedures. The aim of this study was to investigate the possible factors that may be responsible for such burns. Experiments were performed to investigate three possible mechanisms for causing heating in copper wire during MRI: direct electromagnetic induction in a conductive loop, induction in a resonant conducting loop, and electric field resonant coupling with a wire (the antenna effect). Maximum recorded temperature rises were 0.6 degrees C for the loop, 61.1 degrees C for the resonant loop, and 63.5 degrees C for the resonant antenna. These experimental findings suggest that, contrary to common belief, it is unlikely that direct induction in a conductive loop will result in thermal injury. Burn incidents are more likely to occur due to the formation of resonant conducting loops and from extended wires forming resonant antenna. The characteristics of resonance should be considered when formulating safety guidelines.