Doctors battling cancer, which kills nearly eight million people each year globally, have many powerful weapons, including various forms of chemotherapy and radiation. But, what they lack is a reliable method to obtain real-time data about how well a particular therapy is working for any given patient, since patients all respond individually, based on a variety of factors.

Fig. 1 – Once implanted, the sensor wirelessly sends data about biomarkers to an external “reader” device, allowing doctors to better monitor a patient’s progress and adjust or switch therapies. (Credit: MIT)
While magnetic resonance imaging (MRI) and other scanning technologies can indicate the size of a tumor, most detailed information about how well a treatment is working comes from pathologists’ examinations of tissue taken in biopsies. Yet these methods offer only snapshots of tumor response, and the invasive nature of biopsies makes them a risky procedure that clinicians try to minimize.

Now, a team of researchers at MIT’s Koch Institute for Integrative Cancer Research is closing that information gap by developing a tiny biochemical sensor that can be implanted in cancerous tissue during the initial biopsy. The sensor then wirelessly sends data about telltale biomarkers to an external “reader” device, allowing doctors to better monitor a patient’s progress and adjust dosages or switch therapies accordingly. Making cancer treatments more targeted and precise would boost their efficacy while reducing patients’ exposure to serious side effects.

How It Works

The sensors they developed provide real-time, on-demand data concerning two biomarkers linked to a tumor’s response to treatment: pH and dissolved oxygen. When cancerous tissue is attacked by chemotherapy agents, it becomes more acidic. The researchers say that it is possible to see the response chemically before a tumor actually shrinks. In fact, they say, some therapies will trigger an immune system reaction, and the inflammation will make the tumor appear to be growing, even while the therapy is effective. (See Figure 1)

Oxygen levels, meanwhile, can help doctors gauge the proper dose of a therapy such as radiation, since tumors thrive in low-oxygen (hypoxic) conditions. The more hypoxic the tumor is, the more radiation you need. Reading these sensors over time could let doctors see how hypoxia was changing in the tumor, so they could adjust the radiation accordingly.

The sensor housing, made of a biocompatible plastic, is small enough to fit into the tip of a biopsy needle. It contains 10 microliters of chemical contrast agents typically used for MRI and an onboard circuit to communicate with the external reader device.

Empowering the Device

Devising a power source for these sensors was critical, they explain. Four years ago, an MIT team built a similar implantable sensor that could be read by an MRI scanner. But, MRI scans are expensive and not easy to make part of routine care. The researchers wanted to take the next step and put some electronics on the device so they could take these measurements without an MRI.

For power, these new sensors rely on the reader. There is a metal coil inside the reader and a much smaller coil in the sensor itself. An electric current magnetizes the coil inside the reader, and that magnetic field creates a voltage in the sensor’s coil when the two coils are close together, called mutual inductance. The reader sends out a series of pulses, and the sensor answers. A computer, to which the reader is wired, interprets the variation in this return signal over time, which reveals changes in the targeted biomarkers.

Other Applications

The team successfully tested the sensors in lab experiments, including implanting them in rodents. While the sensors were only implanted for a few weeks, they believe the sensors could be used to monitor a person’s health over many years.

Their initial experiments showed that the sensors could quickly, reliably, and accurately detect pH and oxygen concentration in tissue. The researchers next want to see how well the sensors do measuring changes in pH over an extended period of time.

While the primary application of these sensors would be cancer care, the researchers are eager to collaborate with researchers in other fields, such as environmental science.

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Medical Design Briefs Magazine

This article first appeared in the November, 2015 issue of Medical Design Briefs Magazine.

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