SPECIAL MRI MEASURES BLOOD VOLUME, CELL DENSITY IN BRAIN TUMORS, CAN DETERMINE IF TREATMENT IS WORKING, STUDY SHOWS
Embargoed for Release until 4 p.m. CT Sunday, Aug. 4, 2013
Ashley Moses, PCI
INDIANAPOLIS – Rather than waiting until after treatment to see if brain tumors shrink, doctors could use a special type of magnetic resonance imaging (MRI) during treatment to determine if it is working, suggests a study being presented at the 55th Annual Meeting of the American Association of Physicists in Medicine (AAPM).
Researchers used imaging tests called dynamic contrast-enhanced MRI (DCE-MRI) and diffusion weighted MRI (DW-MRI) – which measure blood volume and cell density – to assess the response of brain tumors two weeks after radiation treatment. Tumors that had decreased blood volume and cell density responded to therapy.
To gauge the success of treatment, patients typically undergo standard MRI or computed tomography (CT) imaging after therapy is completed, to determine whether or not the tumor has decreased in size. However, even when treatment has worked, the tumor may not shrink for a month or more.
“Even if a tumor is response to a treatment, its size looks the similar on a CT or MRI for quite awhile until the body starts to absorb the tissue,” said Yue Cao, Ph.D., professor of radiation oncology, radiology and biomedical engineering at the University of Michigan, Ann Arbor. “In the meantime, the patient has continued to undergo treatment that may not be working, therefore missing out on the opportunity to move on to a different or more powerful therapy.”
Researchers used DCE-MRI and DW-MRI to image the brains of 24 patients two weeks after starting radiation therapy to treat a total of 67 brain tumors. All 24 patients also had a standard MRI one month after treatment to determine if the tumors had shrunk. DCE-MRI and DW-MRI images revealed 24 tumors (out of 64) showed decreases in density and/or abnormal blood volume two weeks after starting therapy, meaning they responded to therapy, which was confirmed by the one-month standard MRI.
Researchers used DCE-MRI to quantify additional information about the tumor, which could be used in the future to quickly assess whether treatment is working. The research also reflects that tumors themselves are not uniform, suggesting parts of them may respond to therapy while other parts do not. A related study by the same group shows DCE-MRI can also measure early treatment response in liver tumors.
“If these findings bear out, MRI with perfusion and diffusion could be used to measure the effect of treatment earlier, e.g., during therapy, instead of waiting until treatment has been completed,” said Dr. Cao. “If even a portion of the tumor is not responding, that would signal doctors to try more intensive therapy.”
In addition to Dr. Cao, co-authors of the brain tumor study being presented at AAPM are: R. Farjam, C. Tsien, F. Feng, D. Gomez-Hassan, J. Hayman and T. Lawrence. Authors of the liver study in addition to Dr. Cao are: H. Wang, R. Farjam, M. Feng, R. Ten Haken and T. Lawrence.
About Medical Physicists
If you ever had a mammogram, ultrasound, X-ray, MRI, PET scan, or known someone treated for cancer, chances are reasonable that a medical physicist was working behind the scenes to make sure the imaging procedure was as effective as possible. Medical physicists help to develop new imaging techniques, improve existing ones, and assure the safety of radiation used in medical procedures in radiology, radiation oncology and nuclear medicine. They collaborate with radiation oncologists to design cancer treatment plans. They provide routine quality assurance and quality control on radiation equipment and procedures to ensure that cancer patients receive the prescribed dose of radiation to the correct location. They also contribute to the development of physics intensive therapeutic techniques, such as stereotactic radiosurgery and prostate seed implants for cancer to name a few. The annual meeting is a great resource, providing guidance to physicists to implement the latest and greatest technology in a community hospital close to you.
The American Association of Physicists in Medicine (www.aapm.org) is a scientific, educational, and professional organization with nearly 8,000 medical physicists. Headquarters are located at the American Center for Physics in College Park, Md.