The cases include a disabling injury to Betty Zollner, 79, of Paynesville, who suffered paralysis and began using a walker this year after misfired treatments damaged a healthy section of her spine near the tumor for which she was being treated.

“There is no way to reverse the damage,” Zollner said. “My prayers aren’t being answered.”

Since last year, the state has been investigating at least three mistakes, called medical events, self-reported by Coborn Cancer Center, according to Health Department records obtained by the Star Tribune. Attorney Josh Tuchscherer of Meshbesher & Spence said he contacted the agency about Meshbesher clients who may have been injured as a result of receiving too much or too little radiation from treatments at Coborn.

A Health Department spokesman would confirm only that Coborn is the target of an active investigation over reports of radiotherapy errors. The top official with CentraCare Health, which operates the cancer center, said he didn’t know if the Health Department was reviewing any cases beyond the three events Coborn reported in November.

The radiation errors were discovered after several employees connected to patient radiation treatment plans raised concerns. After the errors were reported to the Health Department, CentraCare conducted an internal audit and found variances in treatment plans for another “small number” of patients, CentraCare President Kenneth Holmen said this week.

Letters were sent to those patients. Holmen said they didn’t suffer serious injuries. Staffing and protocol changes were made, and personnel with leadership roles in the radiation oncology department at Coborn are no longer employed at CentraCare, he said.

While Zollner’s error was reported to the Health Department in November, she didn’t receive notification from CentraCare until March. A meeting with a doctor and company official offered few answers, she said.

Radiation has become an increasingly precise business, with advances such as intensity modulation, which uses multiple pencil-sized beams of photons to target tumors and limit exposure to nearby healthy tissue. Radiotherapy centers are required under state law to report instances in which a single treatment results in 50 percent more or less radiation than planned, or more than 50 percent of radiation than was planned to an unintended body part.

Total doses of radiation to combat tumors are often broken into multiple treatments, but the state must also be notified when a patient’s total radiation dosage is 20 percent greater than planned.

Minnesota cancer centers have self-reported 26 medical events since 2006, according to Health Department records. In that time, Coborn has made six reports — the most by any cancer or radiotherapy center in the state.

The most recent report by Coborn, made in 2014, includes the injury to Zollner and two other incidents involving excessive radiation to unintended body parts. After reviewing the incidents, the Health Department told CentraCare there were “no reportable issues” with two of them and accepted corrective action Coborn already had taken on the third, Holmen said.

“We aren’t trying to hide anything,” he said. “We are having an ongoing dialogue with the Health Department on the complexity of the issues.”

Serious injuries rare

When Zollner learned about the tumor on her mid-spine in spring 2013, she’d spent five years free of an earlier breast cancer. Retired after a long career as the College of St. Benedict’s registrar degree auditor, she’d been enjoying polka dancing and international trips with her husband, Fred.

So she was relieved when her oncologist told her she wouldn’t die from her latest bout with cancer. She underwent 20 radiation sessions and was assured that it was gone.

But in July 2014, she started to feel numbness in her feet. Following an MRI in February, doctors diagnosed transverse myelitis, which will slowly take away movement in her lower body, she said. Radiation to treat Zollner’s cancer had damaged healthy tissue several centimeters above the tumor, Tuchscherer said.

Few reported medical events result in such injuries, said Sherrie Flaherty, supervisor of the Health Department’s radioactive materials unit. In the course of treating a patient, radiologists, physicists and technicians at cancer centers frequently review whether the treatment matches the initial plan. They can catch variations before patients suffer damage.

“So we don’t typically see a lot of patient harm that can’t be corrected,” Flaherty said. “That’s not to say it doesn’t happen, but it’s not very often.”

It’s rare for radiation errors in Minnesota to involve equipment malfunctions, she added. Most events involve human error, such as entering the incorrect dosage into a computer or misaligning patients so that radiation beams are centimeters or even millimeters off target.

“If you need to shift a patient to the left and you shift them to the right … you can still hit the target area, but you might end up with a dose to a lung or some other tissue that you weren’t really intending to hit,” Flaherty said.

In Health Department documents regarding Zollner’s case (her name wasn’t specifically listed), a spot outside the tumor had received 88 percent greater radiation than the prescribed tumor dose. The quality checks in place did not catch the excessive dose, the documents say.

Tony Murphy, radiation safety officer at St. Cloud Hospital, wrote that although treatment of the tumor was delivered accurately, radiation of the spot outside the tumor wasn’t discovered until the audit.

A medical report from one of Zollner’s physicians stated that her paralysis “is almost certainly related to the radiation she received.”

Holmen wouldn’t discuss Zollner’s case, but said he sympathizes because treating cancer is a “profoundly ugly and personal experience.”

Complexity creates risk

By its nature, radiation exposes patients to a therapy that is toxic while seeking to minimize damage. Pre-treatment planning often involves “phantom” treatments to make sure radiation is delivered at the proper angles and strength before patients are placed in front of the beams. Safety checklists are completed before treatment starts.

Technological advances include radiotherapy equipment that automatically moves and adjusts as patients breathe, and accelerators that zap protons at patients instead of photons, because they can be halted at the site of a tumor and don’t travel through the rest of the body. But new technology raises the potential for mistakes as well.

“It’s absolutely more complicated,” said Dr. Kathryn Dusenbery, head of therapeutic radiology for the University of Minnesota Medical Center. “It’s better for the patient in the long run, because you can get less dose to the normal tissue [around a tumor]. But with each thing you add on, there are more places that can go wrong, and the more scrutiny you have to have of your plan to make sure it is correct and safe.”

In addition to being operated by CentraCare, Coborn in 2012 became the first cancer center in the United States to join the Mayo Clinic Cancer Care Network. That gives Coborn practitioners access to Mayo expertise on tumors.

A spokesman for Mayo in Rochester said its leaders are aware of the issues at Coborn and are providing suggestions and oversight to improve the quality of its radiotherapy treatments.

Tuchscherer said his firm is working with national leaders in radiation safety, medical physics and radiation oncology to help people get answers and learn what impact potential errors will have on their lives.

Zollner said she doesn’t want pity.

“I’m still a bit in denial,” she said. “Maybe it won’t get that bad. You just hope.”