Biomarker may measure brain tumor response to RT

Diffusion abnormality index has emerged as a potential biomarker to measure brain tumor response to radiation therapy (RT), according to research presented at the 2013 Cancer Imaging and Radiation Therapy Symposium Feb. 9 in Orlando, Fla. The symposium is sponsored by the American Society for Radiation Oncology and the Radiological Society of North America.  

Reza Farjam, a PhD candidate in bioengineering and radiation oncology at the University of Michigan in Ann Arbor, and colleagues enrolled 20 patients with brain metastases treated with whole-brain RT in the study. A total of 45 lesions among the patients were categorized as follows: 16 responsive, 18 stable and 11 progressive lesions.

The researchers acquired diffusion measurements prior to radiation therapy, two weeks after the start of treatment and one month after treatment completion. They devised a normal tissue apparent diffusion coefficient histogram for each patient and divided the tumor apparent diffusion coefficient histograms into three regions: low (high cellularity), normal and high (edema and necrosis) diffusion.

Farjam and colleagues then developed the diffusion abnormality index, which included low and high apparent diffusion coefficient contributions, to predict tumor response.

The researchers evaluated sensitivity and specificity of the change in diffusion abnormality index from pre-treatment to the end of therapy and compared them with the changes in gross tumor volume from pre-treatment to the end of therapy.   

The percentage decrease in diffusion abnormality index from pre-treatment to two weeks after the start of treatment was significantly greater in responsive tumors than in stable and progressive ones, reported Farjam et al in the study abstract. The receiver operating characteristic analysis showed that this change in the diffusion abnormality index was a significantly better predictor of post-treatment response than a change in gross tumor volume, suggesting that physiological change precedes volumetric change, according to the researchers.

Farjam et al concluded that diffusion abnormality index could be a better diffusion imaging biomarker for early assessment of tumor response to therapy.