“It’s a fake wall,” she said. “See?”

A PhD-credentialed physicist was acting as our tour guide and extended her hand over a spot on the wall just beyond where we were standing, beside a multi-million-dollar cancer-targeting machine. She pushed against the spot and a hinged panel that extended to the floor swung open – a hidden door. We walked through it, entered a small room, and stared at the electrical guts and plumbing of a “linac” or linear accelerator.

“All this tubing and wiring creates high-energy light, that we call photons,” she said. “The shielded bunker we are standing in keeps this radiation contained to kill cancer cells but harm no one else.”

The engineering seemed complex to me then – I had just begun radiation training at UC Davis. My physics education would continue another four years, teaching me about the bunker walls of concrete – six feet deep – and thick motorized metal doors lined with the element Boron. Boron captures dangerous stray radiation particles called neutrons and then splits itself into the stable atoms of Lithium and Helium to neutralize the threat – like an act of self-sacrifice.

Yes, the linac sound complicated, but it just makes light. Imagine it like a large flashlight. A normal flashlight only shines visible light, which bounces off objects, ricochets in every direction nearly instantaneously, hits our eyes, and gives us sight of the world surrounding us. Light travels as a wave moving up and down – the faster the oscillation, the more up and downs and the higher its energy. Slowing down the oscillation makes the up-and-down waves longer and lowers their energy. We perceive light that is moving up and down at different rates as different colors. When light travels through rain, the droplets act like a prism and bend the light. How much each waves beds depends on how fast it is moving up and down – like a curve on a racetrack. Red light is slowest on the outside track and purple is fastest on the inside track – the bend separates the waves of light into color groups – making a rainbow appear in the sky for our enjoyment. Amazingly and counter-intuitively, waves of light can oscillate up and down at speeds that our eyes can’t detect. Light oscillating at rates slower than red light is called infra-red light. Everything around us emits infra-red light based on temperature. You can see it if you put on infra-red goggles as thermal night vision.

To explain a linac in simple terms, let’s imagine a flashlight capable of speeding up how fast each light wave bounces up and down. Once you increased the flashlight’s energy, the light beam would seem to disappear from your view once the waves were too energetic for your eye to detect. Light would still be shining, but the energy would be higher than the highest visible energy color – purple. This is ultra-violet light. UV light does not just bounce off everything. It penetrates your body, stopping just below the skin – this is how skin gets sunburned.

If you increased the flashlight’s energy further, the waves would penetrate deeper into your body and at a certain energy, they would travel all the way through you. A portion of this light would be absorbed by your body before the rest passed through. This would cast a type of shadow behind you. While you couldn’t see this shadow with your eyes, you could with a detector film placed behind you to catch light as it leaves your body – this is an x-ray.

If you dialed up the energy of the flashlight further still, the light waves would oscillate up and down so fast, when they hit your body, they would collide with the cells of your body and damage them as they passed. At this high energy level, light is renamed radiation. Yes, it can be harmful, but it can also be harnessed. Making radiation and aiming it at dangerous cancer cells is the purpose of a linear accelerator – it’s a photon flashlight that can hunt cancer cells.

For Nevada Country cancer patients, a linear accelerator with the most sophisticated techniques for shaping and molding clouds of radiation is available locally. This linac strategically and precisely places radiation inside the body to kill cancer cells, while minimizing damage to normal neighboring cells.

Dr. Hess is the Medical Director of Radiation Oncology at Sierra Nevada Memorial Hospital. Dr. Hess’ views are his own and do not reflect official positions of CommonSpirit Health, Dignity Health, or Sierra Nevada Memorial Hospital. Some aspects of this article are fictionalized history but based on a true story. All names are fictitious to protect patient confidentiality.

Gold Country Senior Services Executive Director Janeth Marroletti’s recent resignation marks a major change for the nonprofit.

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