The ‘good guys’ (healthy cells) vs. the ‘bad guys’ (cancer cells)

By Susan Williams

“The basic idea of radiation therapy is to kill cancer cells—bad guys—in a tumor while sparing the cells in healthy tissue—good guys,”

John Cameron, director of the IUFC

“The basic idea of radiation therapy is to kill cancer cells—bad guys—in a tumor while sparing the cells in healthy tissue—good guys,” he said. “But the devil, as always, is in the details. In this case, the bad guys are generally surrounded by good guys and the question is, how can one get to the former without doing too much collateral damage. Sounds kind of militaristic.”

Major weapons involved in the battle, said Cameron, are photons, which are utilized in traditional radiation therapy, and protons, used in proton therapy, such as that IUCF’s Midwest Proton Radiation Institute will utilize in the treatment of cancer. Photons, or X-rays, are massless and have no electric charge, he said, while, in contrast protons are heavily charged particles.

“Skipping a little physics here,” Cameron continued, “the result is that the ways in which the two different particles deposit energy to kill cells are very different. The photon does most of its damage right at the surface of a material and has a steadily reducing effect at greater depths. In contrast, protons do relatively little damage at the surface and concentrate their greatest effect in a small distance close to their maximum range.

“Note there is no mention of a well-defined maximum range for the photons. This feature is another major advantage of protons. It means that beyond some well-defined distance, protons do no damage, allowing one to come close to critical organs but not damage them in any way.”

Cameron explained that the nature of proton energy delivery is especially important in treating childhood cancers.

“While killing the good guys is never good, it is of greatest importance for pediatric patients where the concern of malformations and of later stage tumors resulting from traditional radiation itself are of great concern.”

The IU cyclotron’s role in the battle against cancer comes in when it’s time to get the protons moving—fast.

“One has to vary the energy of the proton beam to get to the maximum range I mentioned,” said Cameron. “To reach a depth of 28 centimeters, which is more than half the diameter of most Hoosiers, the beam must be going at half the speed of light. Our cyclotrons are capable of giving just the needed amount of energy to protons.”