While pregnant with her first child, Rhea Birusingh started experiencing blurry vision that her OB-GYN dismissed as an expected pregnancy-related change, but three months later, she went to her ophthalmologist, who discovered an inoperable 2-centimeter benign brain tumor behind her right eye. Now, nearly four months later, Birusingh’s son is healthy and her vision is normal, thanks to a powerful, precise radiation treatment.

“When you’re a pathologist and your eyes are a money maker, you start to get a little bit worried,” Birusingh, 37, of Howey-in-the-Hills, Florida, told FoxNews.com.

Doctors at UF Health Cancer Center – Orlando Health decided to use the treatment, called proton beam therapy, because Birusingh’s tumor was adjacent to her hippocampus, which is critical for short- and long-term memory and learning. Proton beam therapy works differently from conventional radiation treatments, which rely on X-rays. Birusingh was the first patient to undergo the treatment— which uses a three-story, 200,000 pound machine— at the hospital.

“Protons are another form of radiation, a charged particle from the nucleus that accelerates to six-tenths the speed of light,” Dr. Naren Ramakrishna, the director of proton therapy at UF Health Cancer Center – Orlando Health, told FoxNews.com. “There’s no radiation beyond the point where they release a big burst of energy, so we can treat tumors in a way that is effective while delivering little or no radiation to normal body parts.”

When a conventional X-ray enters the body, it emits a high dose of radiation that decreases as it passes through the body, but the energy never drops to zero. Multiple beams intersect at a tumor, with the strongest dose at the intersection, but the beam surpasses the tumor, meaning radiation reaches surrounding body parts, increasing the risk of side effects like skin problems, fatigue and nausea.

With proton beam therapy, two or three beams of particles deposit their energy directly into the tumor, so little to no radiation goes beyond the tumor to surrounding structures. The proton beam reaches the tumor, releases its highest dose, and then no energy remains.

“It’s a very critical advantage, especially in sensitive parts of the body like the brain or for children,” Ramakrishna said.

Proton therapy significantly reduced Birusingh’s radiation exposure.

“We believe that even really low doses of radiation can result in impairment in hippocampus function long term,” Ramakrishna said. “The dose that would’ve been delivered using X-rays would have been more than 10 times greater.”

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The tumor was also close to her hypothalamus, which creates hormones. The X-ray dosage would have been 80 percent higher than what the team was able to do with proton therapy.

“For a young person like Rhea with a tumor in a critical location, like the brain, protons allow us to treat in a way that is going to benefit [her] not just now, but throughout her life,” Ramakrishna said.

But before doctors could treat the tumor, they needed to care for her unborn child. Their decision to induce her at 34 weeks was twofold— to avoid any chance of scattered radiation exposure to the fetus and to cut off the tumor’s supply of progesterone, a pregnancy hormone that was fueling its growth. As the tumor grew, it was progressively worsening the function of the nerves that move the eye and expanding toward the vision nerve. These neurological problems would have only continued, increasing the risk of permanent damage the longer she carried the baby.

On Feb. 18, 10 days after her initial diagnosis, Birusingh delivered her son, Zane. A month later, an MRI revealed the tumor had stopped growing.

In early April, Birusingh started her first proton therapy treatment, which required of 29 treatments over six weeks, five days a week. Each treatment lasted about 30 minutes.

Proton  beam therapy was created in the 1940s and 1950s, but as of 1970, it had only been used in four centers worldwide because it required the space to support the 100-ton machine, and a teams of physicists and researchers to support it, Ramakrishna said. Now, there are 23 centers in the United States, with 14 more under construction. Worldwide, there are 40 to 50 devices in operation.

While many of his patients ask if proton therapy, with its precision and lack of side effects, is applicable for their tumors, it remains a limited, expensive resource, Ramakrishna said.

“We have to apply a cost-benefit analysis and understand which of the tumors are going to benefit most from it— those are the type of patients we select for treatment. Not every tumor is going to have a big benefit,” Ramakrishna said, adding that tumors that are not near critical structures and large tumors with ill-defined edges are the type that do not need proton therapy’s precise cutoff.

Proton beam therapy results in fewer side effects because there is less dosage going into supporting tissues. Hair loss and skin changes are possible in the short term, but long term there are fewer risks than conventional X-rays.

Birusingh said she recently started experiencing some hair loss, but she wasn’t sure if it was normal postpartum changes or due to radiation.

She’s experienced some fatigue but attributed that to being a new mom. Zane spent five days in the NICU after being born at 3 pounds, 15 ounces.

“He defied the odds,” Birusingh said. “He did amazingly well.”

Birusingh was the “perfect” first case for Orlando Health’s proton therapy treatment, Ramakrishna noted.

“Proton therapy really presents a pinnacle in terms of medical achievement,” Ramakrishna said. “It really took some of the best minds in the world to come up with kind of device. We’re using this technology to help people in a very direct and meaningful way.”