Small cell cancer is a type of lung cancer that presents in basically two formats. One format is that the disease is actually limited to what classically, in the old days, radiation oncologists called “the box,” meaning that it was limited to the chest. When we talk about limited stage small cell carcinoma, we’re talking, potentially, about a disease that is very responsive to treatment, and sometimes can be cured. When we cure those patients, with a combination of chemotherapy and radiation for limited stage small cell carcinoma, we often look to see if the cancer has spread to the brain. We do this by getting MRI studies of the brain; if there’s no evidence of disease in the brain, and the treatment has effectively worked in the chest at eradicating the disease, we all are very happy.
Unfortunately, if you follow these patients over time, they have a very high chance of having the cancer come back in the brain — the brain is thought to be a sanctuary site, meaning that it doesn’t get the treatment from the chemotherapy that the rest of the body gets, so if any cells have snuck up there, they sometimes can grow without the treatment that’s been delivered so far.
One of the things that we’ve done in the past is deliver a very low dose of radiation to the whole brain, as a prophylactic treatment — that’s often called PCI, or prophylactic cranial irradiation. We offer this routinely to patients with limited stage disease because the studies have demonstrated that if you give prophylactic treatment, you reduce the chances of the cancer coming back in the brain, and if you reduce the chances of the cancer coming back in the brain, you presumably reduce the chances of all those symptoms that cancer in the brain can cause.
We often talk about the brain as being the “high rent district.” If we can keep cancer out of the brain, we can keep people much more functional, not have the risks of strokes, and mental problems, and seizures that cancer in the brain can cause, so we often give prophylactic cranial irradiation.
Prophylactic cranial irradiation is a little bit different than whole brain radiation: the doses that you give each day are lower, the dose that you give overall is lower, because you’re treating disease that you can’t see, you’re not treating the disease that is actually already there — hence the word prophylactic cranial irradiation.