Equipment used to treat cancer patients wasn’t properly shielded
By COLIN M. STEWART
Workers in the Hilo veterans outpatient clinic may have been exposed to radiation over the last six years due to insufficient shielding of a radiation therapy machine located in the downstairs oncology clinic.
The machine, a linear accelerator, is contained in a specially built concrete and lead vault on the ground floor of the Hawaii Pacific Oncology Center on Waianuenue Avenue. Doctors use it to treat cancer patients with a concentrated, high-energy beam of X-rays that destroys cancerous tissue.
On Monday afternoon, Howard Ainsley, CEO of Hilo Medical Center — which operates the oncology clinic — said that medical physicists discovered “an issue” with the accelerator while testing the vault in preparation for upgrading the radiation equipment.
“In early March, we contracted with a medical physicist to survey the room that houses our current linear accelerator to ensure that the room would meet specifications for two different models of linear accelerators being considered for the existing room,” he said.
“A routine part of that review process did entail the ability of the room to shield radiation emitted by the accelerator. On the 16th (of March), he examined the linear accelerator and the room directly above it and found some inconsistencies.”
He added that the accelerator has been routinely tested by the hospital’s radiation safety officer since its installation in 1998, but the “inconsistencies” had not been detected.
According to the medical physicist’s preliminary findings, “when the linear accelerator is operating, there may be radiation levels that exceed regulatory limits for the present occupancy in the rooms above the radiation oncology treatment center,” Ainsley said.
Three small rooms above the accelerator, offices for the Veterans Affairs’ Hilo Community Based Outpatient Clinic, were affected by the higher radiation levels, Ainsley said.
Hilo Medical Center officials contacted the VA the next day, he said, and determined that the three clinic employees would have to be relocated to other rooms.
Ainsley added that the accelerator does not use radioactive isotopes, and only emits radiation when it is switched on intermittently for treatments.
“It’s important to note,” he said, “that the linear accelerator is not broken, and it is not operating improperly. Rather, the configuration of the rooms and the area is different from that which it had previously been.”
Ainsley said the three rooms above the accelerator had previously been used for storage, until they were turned into offices for VA employees in 2006.
The employees who occupied the rooms have been informed of their potential exposure, but no test exists to see how much radiation they may have received, Ainsley said. However, HMC’s contracted medical physicist who performed the tests, Hong Guo, and the hospital’s own radiation safety officer, Harry Palmer, have been able to estimate the employees’ potential exposure.
“The occupants that were in position to be exposed, that exposure was intermittent, so their actual exposure depends on whether they were present and the strength of the beams being used,” Ainsley said.
In a March 18 letter to the Department of Veterans Affairs, Hilo Medical Center Hospital Systems Services Director Julie-Beth Ako provided the physicists’ estimates for potential exposure for the years 2006-2011, from the time the upstairs rooms were occupied until the time the radiation was discovered.
While the exposure numbers are small, they are enough to cause limited health risks, according to the U.S. Nuclear Regulatory Commission.
Between 2006 and 2011, people occupying the rooms above the linear accelerator could have received an average of 353 millirems of radiation per year. Comparatively, the average exposure from a single abdominal X-ray is 300 millirems, the exposure from a dental X-ray is 200 millirems, and a single chest X-ray equals about 20 millirems.
A table of comparative health risks provided by the NRC reveals that while smoking 20 cigarettes a day can result in an estimated life expectancy loss of six years, and being 15 percent overweight can total two years, a dose of 300 millirems per year equals about 15 days of life expectancy lost.
The NRC allows 500 millirems of exposure per year for health care workers, while the general public should be exposed to no more than 100 millirems per year. By those figures, Ainsley said, the VA workers had the potential of being exposed each year to more than three times the NRC’s allowable limit, or ALARA limit, which stands for “as low as reasonably achievable.”
Veterans Affairs officials in Honolulu and Hilo had yet to respond to requests for comment as of Tuesday evening. However, Ainsley said he had personally been in contact with various VA officials, and HMC is working closely with them to complete testing of the vault and to prevent further exposures to the radiation.
As for what that solution would be, Ainsley said that the three rooms would more than likely remain empty. He couldn’t say what repairs, if any, could be made.
“It’s set in concrete,” he said, “there’s nothing wrong with the room or the machine. Ultimately, we’d have to limit the occupancy upstairs. … Those rooms won’t be reoccupied unless they’re safe.”
Ainsley said he expects monitoring of the vault and the VA to continue for the next couple of months.
“We’re going through the testing phase right now, and we’re looking at July hopefully having this resolved,” he said.
According to the website radiologyinfo.org, patient and therapist safety is of utmost concern when dealing with linear accelerators. The radiation therapist watches the patient through a closed-circuit television monitor during treatments. A linear accelerator should be situated in a room with lead and concrete walls, “so that the high-energy X-rays are shielded. The radiation therapist must turn on the accelerator from outside the treatment room.”
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