What is Proton Therapy
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What happens to a Tumor during Proton Therapy?

What happens to a Tumor during Proton Therapy?

To understand what happens to a tumor after it receives proton therapy (or any form of radiation), it is important to understand what a cancer cell actually is. Normal cells die when they become damaged, and new cells take their place. A cancer cell is a cell that has been damaged and continues to divide and replicate without stopping.

When cancer is irradiated, it breaks its strands of DNA, disrupting the blueprint that the cancer uses to reproduce. The cancer cell could live forever with these defective DNA strands, but when it does divide (which is, after all, the problem with cancer cells) it creates daughter cells that cannot live because of the defects in their construction. Therefore, it may take weeks or months for cancer cells to die after being irradiated, depending on how often that particular cancer cell population divides.

As the cells die, the body creates an inflammatory response (as it does whenever there is injury to tissue – benign or malignant). Much of the cellular debris is cleared by the immune system. As the cancer cell membranes leak their contents into the surrounding space, immune cells, like macrophages, ingest the cellular debris and then take it away through the lymphatic channels or the bloodstream. Sometimes the debris can’t be completely cleared, and fibrous (scar) tissue forms in place of what had been the tumor.

This is why we sometimes see a residual mass where the tumor had been. Thus, it may take months to confirm that the cancer cells have actually died, since there is still a mass where the tumor had been. PET scans are helpful in these cases to verify that the tumor activity has gone away, even though a mass may remain.

PET scans are not so helpful in some areas, such as the brain, where we depend on MRIs to assess tumor response. In that case, if the tumor is shrinking or staying the same size, we can be pretty confident there are not viable tumor cells present. We only start to worry if it gets bigger again. The longer we follow a residual mass that is staying the same size, the more confident we can be that it is just scar tissue and not residual tumor.

In some locations, such as inside the esophagus, bronchus, bowel or bladder, some of the dead tumor cells actually slough into the interior to be swallowed, coughed out or excreted by the body, while the immune system takes away the rest.

This great write-up of what happens to a tumor during treatment originally came from Gary L. Larson, MD.