 After baseline staging including PET and CT scans PET0 CT0, performed on PET scanners approved for the purpose by The PET Imaging Centre at St ThomasGuys, all eligible and consenting patients will receive an initial 4 cycles of brentuximab vedotin following which response and continuation of brentuximab vedotin will be assessed by PET PET4 in the first instance. Patients achieving CMR Deauville score 1-3 will continue treatment. Patients achieving PMR Deauville score 4,5 with uptake less than baseline will also continue treatment. Patients achieving NMR Deauville score 4,5 with no change in uptake from baseline or PMD Deauville score 4,5 with increased intensity of uptake compared to baseline andor new lesions consistent with lymphoma will stop brentuximab vedotin and be considered for alternative therapy. 