Pediatric lymphoma: metabolic tumor burden as a quantitative index for treatment response evaluation

Metabolic tumor burden (MTB) incorporates the advantages of the existing indices: the metabolic volume of the lesion calculated by size-dependent thresholding on positron emission tomography-computed tomography (PET-CT) along with its aggressiveness as determined by standardized uptake value (SUV). This study was conducted to investigate whether MTB can be used as an objective index for monitoring therapy response in pediatric lymphoma.

Forty-two pediatric patients (35 male and 7 female) with histologically proven lymphomas (26 Hodgkin's and 16 non-Hodgkin's) were evaluated. MTB was assessed in baseline, early interim (after 2 cycles) and post-therapy PET-CT studies using RT_Image software. Size-dependent thresholding based on a phantom study conducted at our institute was used for the calculation of metabolic tumor volume (MTV). MTB was given as the product of MTV and the SUVmean. Summation of MTB from all lesions gave the whole body MTB. Baseline, early interim and post-therapy SUVmax and whole body MTB of the partial and complete response group were compared.

Of 42 patients, 37 had complete response and 5 had partial response at the end of therapy based on clinical, CECT and bone marrow biopsy findings. SUVmax showed an overall reduction of 87.4% while MTB showed a reduction of 96.4% between baseline and early interim PET-CT scan. Similarly, SUVmax showed an overall reduction of 95.2% while MTB showed a reduction of 99.6% between baseline and post-therapy scan. There was significant difference between MTB of partial response and complete response group at baseline and early interim PET-CT (p 0.031 and 0.012, respectively). No such significant difference was found for SUVmax.

Whole body MTB appears to be useful quantitative parameter for the assessment of treatment response using PET-CT in pediatric lymphoma patients.