Effect of radiochemotherapy on T2* MRI in HNSCC and its relation to FMISO PET derived hypoxia and FDG PET

Abstract

Background: To assess the effect of radiochemotherapy (RCT) on proposed tumour hypoxia marker transverse relaxation time (T2*) and to analyse the relation between T2* and 18 F-misonidazole PET/CT (FMISO-PET) and 18 F-fluorodeoxyglucose PET/CT (FDG-PET). Methods: Ten patients undergoing definitive RCT for squamous cell head-and-neck cancer (HNSCC) received repeat FMISO- and 3 Tesla T2*-weighted MRI at weeks 0, 2 and 5 during treatment and FDG-PET at baseline. Gross tumour volumes (GTV) of tumour (T), lymph nodes (LN) and hypoxic subvolumes (HSV, based on FMISO-PET) and complementary non-hypoxic subvolumes (nonHSV) were generated. Mean values for T2* and SUVmean FDG were determined. Results: During RCT, marked reduction of tumour hypoxia on FMISO-PET was observed (T, LN), while mean T2* did not change significantly. At baseline, mean T2* values within HSV-T (15±5ms) were smaller compared to nonHSV-T (18±3ms; p=0.051), whereas FDG SUVmean (12±6) was significantly higher for HSV-T (12±6) than for nonHSV-T (6±3; p=0.026) and higher for HSV-LN (10±4) than for nonHSV-LN (5±2; p≤0.011). Correlation between FMISO PET and FDG PET was higher than between FMSIO PET and T2* (R 2 for GTV-T (FMISO/FDG)=0.81, R 2 for GTV-T (FMISO/T2*)=0.32). Conclusions: Marked reduction of tumour hypoxia between week 0, 2 and 5 found on FMISO PET was not accompanied by a significant T2*change within GTVs over time. These results suggest a relation between tumour oxygenation status and T2* at baseline, but no simple correlation over time. Therefore, caution is warranted when using T2* as a substitute for FMISO-PET to monitor tumour hypoxia during RCT in HNSCC patients.