Every year, tens of thousands of people world-wide have brain surgery without a single incision: there’s no scalpel, no operating table, and the patient loses no blood. Instead, this procedure takes place in a shielded room with a large machine that emits invisible beams of light at a precise target inside the brain.
This treatment is called stereotactic radiosurgery, and those light beams are beams of radiation: their task is to destroy tumors by gradually scrubbing away malignant cells.
For patients, the process begins with a CT-scan, a series of x-rays that produce a three-dimensional map of the head. This reveals the precise location, size, and shape of the tumor within. The CT-scans also help to calculate something called "Hounsfield Units," which show the densities of different tissues. This offers information about how radiation will propagate through the brain, to better optimize its effects. Doctors might also use magnetic resonance imaging, or MRI’s, that produce finer images of soft tissue, to assist in better outlining a tumor’s shape and location.
Mapping its precise position and size is crucial because of the high doses of radiation needed to treat tumors. Radiosurgery depends on the use of multiple beams. Individually, each delivers a low dose of radiation. But, like several stage lights converging on the same point to create a bright and inescapable spotlight, when combined, the rays of radiation collectively produce enough power to destroy tumors.
In addition to enabling doctors to target tumors in the brain while leaving the surrounding healthy tissue relatively unharmed, the use of multiple beams also gives doctors flexibility. They can optimize the best angles and routes through brain tissue to reach the target and adjust the intensity within each beam as necessary. This helps spare critical structures within the brain.
But what exactly does this ingenious approach do to the tumors in question?
When several beams of radiation intersect to strike a mass of cancerous cells, their combined force essentially shears the cells’ DNA, causing a breakdown in the cells’ structure. Over time, this process cascades into destroying the whole tumor. Indirectly, the rays also damage the area immediately surrounding the DNA, creating unstable particles called free radicals. This generates a hazardous microenvironment that’s inhospitable to the tumor, as well as some healthy cells in the immediate vicinity. The risk of harming non-cancerous tissue is reduced by keeping the radiation beam coverage as close to the exact shape of the tumor as possible.
Once radiosurgery treatment has destroyed the tumor’s cells, the body’s natural cleaning mechanism kicks in. The immune system rapidly sweeps up the husks of dead cells to flush them out of the body, while other cells transform into scar tissue.
Despite its innovations, radiosurgery isn’t always the primary choice for all brain cancer treatments. For starters, it’s typically reserved for smaller tumors. Radiation also has a cumulative effect, meaning that earlier doses can overlap with those delivered later on. So patients with recurrent tumors may have limitations with future radiosurgery treatments.
But these disadvantages weigh up against some much larger benefits. For several types of brain tumors, radiosurgery can be as successful as traditional brain surgery at destroying cancerous cells. In tumors called meningiomas, recurrence is found to be equal, or lower, when the patient undergoes radiosurgery. And compared to traditional surgery— often a painful experience with a long recovery period— radiosurgery is generally pain-free, and often requires little to no recovery time.
Brain tumors aren’t the only target for this type of treatment: its concepts have been put to use on tumors of the lungs, liver, and pancreas. Meanwhile, doctors are experimenting with using it to treat conditions such as Parkinson’s disease, epilepsy, and obsessive compulsive disorder. The pain of a cancer diagnosis can be devastating, but advancements in these non-invasive procedures are paving a pathway for a more gentle cure.
