Study Suggests Delivering Different Radiation Doses to a Tumor Could Make Immunotherapy Drugs More Effective

A new study in mice shows that “delivering different doses of radiation to a tumor revs up the immune system and allows it to detect not only the treated tumor but distant tumors that were not irradiated.”

According to the researchers, “when mixed dose radiation is followed with immunotherapy drugs called immune checkpoint inhibitors, it makes the drugs more effective at killing cancer cells throughout the body than when radiation was delivered at a single dose level.”

The team used “brachytherapy,” which is a “targeted approach that inserts a radioactive source into a tumor using a catheter. This delivers a gradient of radiation from high dose near the catheter to low dose at regions of the tumor that are most distant from the catheter.” The study showed that “each dose leads to a unique immune response: the high dose kills cancer cells in the immediate region of the tumor, the medium dose promotes an immune process called a type I interferon response that plays an essential role in activities like fighting against viruses, and the low dose promotes inflammatory signaling and changes in nearby blood vessels to enable greater trafficking of immune cells into the tumor.”

The researchers also determined that “each dose of radiation causes unique changes in gene expression and the susceptibility of the cancer to immunotherapy drugs. The mixed dose treatment was most effective at boosting tumor-specific T-cells, a type of immune cell that can find cancer cells elsewhere in the body and attack them.”

The team believes that the study’s results “point to new approaches to optimally using radiation to treat patients whose cancers have stopped responding to immunotherapy drugs.”