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Imaging biomarkers come to the fore
17.35 Monday CT: Using medical images to gauge a patient’s response to treatment is nothing new. But with the emergence of advanced imaging methods, and applications like drug development becoming increasingly reliant on such techniques, the use of imaging as a biomarker for therapeutic response has become a prominent area of research. So much so that “Imaging as a Biomarker for Therapy Response” was chosen as the theme for this year’s AAPM President’s Symposium.
The symposium kicked off with Lawrence Schwartz of the Memorial Sloan Kettering Cancer Center (New York, NY) telling delegates about the intense interest in using imaging biomarkers for new drug development and drug discovery. Here, imaging is used to test the efficacy of potential drugs via direct visualization and quantification of changes in physiological processes following treatment. Imaging also offers a noninvasive means by which to assess the safety of a new drug.
The process of developing any new drug is a long and complex procedure. On average, a pharmaceutical company will shell out $802 million over 15 years to bring one new drug to market, with 99 other drugs typically discarded along the way. Anything that can speed this process is obviously of great interest.
“Imaging is more and more important in drug development,” concurred Michael Vannier of the University of Chicago (Chicago, IL). “There is an opportunity here for imaging to remove materials that won’t succeed in the long term at an earlier stage, thereby reducing the cost and saving time.”
In particular, Schwartz believes that imaging biomarkers will play a key role in the development of targeted molecular therapies for cancer treatment. One technique that has proven invaluable is PET-CT, which can assess the impact of a treatment on tumour metabolism. Importantly, PET-CT can detect metabolic changes before any change in the tumour size is observed, providing an early predictor of therapeutic response. Schwartz also cited dynamic contrast-enhanced MRI, which can monitor changes in tumour vascularity.
There’s still work to be done here, however. Vannier reckons that the full potential of imaging biomarkers cannot be realized without stringent quality control, the development of data repositories and a “community effort” to validate new techniques. “There’s a critical and immediate need for the medical physics community to get involved in imaging biomarkers,” he told delegates.
• In addition to the important application of drug development, imaging still has a big role to play in measuring treatment response and potentially providing a prediction of therapeutic outcome.
One such method was the subject of a presentation at Varian Medical Systems’ Emerging Technologies Symposium held in the nearby Hyatt Regency hotel. Daniel Hamstra, a clinical lecturer in the University of Michigan’s department of radiation oncology (Ann Arbor, MI), told Varian’s guests about the potential of diffusion MRI for early response evaluation.
Diffusion MRI, he explained, measures the “thermally driven molecular motion of water” within tissue. Following treatment, the tumour’s cellular membranes break down, which results in an increased mobility of water within the tissue. Diffusion MRI can pick up such histological changes, which occur much sooner than any changes in the tumour’s overall volume. The diffusion MRI data also show potential as an early predictor of overall survival or time-to-progression.
“Ten years of preclinical data support the concept of changes in diffusion MRI data acting as an early indicator of tumour response,” said Hamstra, adding that “diffusion is complementary to other measures of response, such as perfusion or PET,” and concluding that a multimodality approach is likely to prove the most favourable way forward.
