Purpose: The added value of baseline positron emission tomography (PET) scans in therapy evaluation in malignant lymphoma is unclear. In guidelines, baseline PET is recommended but not mandatory except in lymphoma types with variable fluoro-D-glucose uptake. The aim of the present study was to test the hypothesis that adding baseline PET information decreases false positive readings with posttreatment PET and improves observer agreement.
Methods: Forty-four patients (mean age 56 years, standard deviation 14) with malignant lymphoma were included. Two nuclear medicine physicians retrospectively and independently evaluated the posttreatment PET, 3 weeks later followed by paired reading of baseline and posttreatment PET. For each PET, 22 regions were classified as positive, negative, or equivocal, resulting in an overall PET score of positive, unclear, or negative. In case of discrepancies, consensus was reached.
Results: Addition of baseline to posttreatment PET evaluation affected the classification of metabolic response in 34% of malignant lymphoma patients treated with first-line chemotherapy. In one out of seven patients, addition of the baseline PET lead to opposite conclusions (95% confidence interval 4-14). False positivity was reduced by adding the baseline scan information, but the effect on false negativity was similar. In addition, the amount of unclear classifications halved after paired reading. Observer agreement did not improve upon adding the baseline PET data.
Conclusion: Without any other clinical information, pretreatment PET facilitates changes the interpretation of a posttreatment PET in a third of the patients, resulting in both upgrading and downgrading of the posttreatment situation of a malignant lymphoma patient. If these results are confirmed for PET-computed tomography systems, they favor the addition of baseline PET to the current work-up of patients with malignant lymphoma.