Combining dynamic contrast enhanced MRI and diffusion weighted MRI to measure blood volume and cell density within brain tumors could provide insight into the success of treatment while it is ongoing, as early as two weeks after the start of radiation therapy, according to a study presented at the 55th Annual Meeting of the American Association of Physicists in Medicine (AAPM).
The findings could lead to the use of perfusion and diffusion MRI for determining early treatment response, rather than using standard MRI or CT after therapy is completed to determine whether or not a tumor has decreased in size, explained Yue Cao, PhD, professor of radiation oncology, radiology and biomedical engineering at the University of Michigan, Ann Arbor, and colleagues.
Results were based on images of 24 patients—with a total of 67 brain tumors—who underwent dynamic contrast enhanced MRI and diffusion weighted MRI after two weeks of radiation therapy. All patients also underwent standard MRI one month after treatment to look at tumor size.
Diffusion MRI is sensitive to the motion of water molecules, and while tumors may not shrink for more than a month as the body absorbs the tissue, this MRI technique can spot earlier changes to tumor density. “Measuring the random movement of water molecules in the tumor before and after starting treatment can tell us if the tumor is responding to the therapy,” said Cao.
The perfusion and diffusion MRI images showed 24 tumors had decreased density and/or abnormal blood volume—signs of treatment response—after two weeks of treatment. This treatment response was later confirmed by the one-month standard MRI.
Cao and colleagues were also able to use the MRI technique to demonstrate that tumors are not uniform, and that some parts may respond to therapy while other parts do not. Imaging may eventually be able to provide an early signal of whether physicians should move on to a more intensive therapy.
The researchers also are working on a related study using dynamic contrast enhanced MRI to measure early treatment response in liver tumors.