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OMNITRON PLANNING TO MODIFY MODEL 2000 CANCER THERAPY DEVICE TO ADDRESS POTENTIAL FOR RADIATION OVERDOSE; NRC REPORT OUTLINES DEVICE "WEAKNESSES"

This article was originally published in The Gray Sheet

Executive Summary

Omnitron plans to modify its high dose rate (HDR) remote afterloader cancer therapy device in order to eliminate the potential for radiation overdose that may result from breakage of a wire used to introduce a radioactive source into a tumor. The company says that the changes to the cancer therapy device will ensure that the operator of the device is informed about whether the radiation source, which is contained in the tip of the introducing wire, has been returned to its "safe box" after completion of a treatment. The company plans to add equipment and software to the system that will measure the physical length of the wire both when it is played out and retracted. The device then will compare the lengths to make sure that they are the same. Omnitron also is going to add an internal monitor to the system that is designed to detect the radioactive source and verify that it has returned to the safe box after treatment. Modifications to the afterloader will be included in all new devices the firm manufactures. The company also plans to modify devices in the field but has not determined whether it will charge the facilities for the alterations. Omnitron and its afterloader system have been under investigation by the Nuclear Regulatory Commission and FDA following two recent incidents of wire breakage in systems operated by Oncology Services, Inc., a firm that runs cancer therapy centers. In the first case, which occurred in November at a center in Indiana, Pennsylvania, the afterloader's wire broke, and the radiation source remained in the patient's body, potentially causing her death five days later. A second incident occurred in Pittsburgh on Dec. 7, but the radiation source was quickly retrieved ("The Gray Sheet" Jan. 4, p. 12). On Dec. 9, NRC issued a directive to facilities licensed to operate the Omnitron afterloader ordering that use of the system be discontinued unless the facility could ensure that the radioactive source can be "expeditiously removed" if the wire were to break. On Jan. 20, NRC suspended Oncology Services' license to operate the afterloaders because of deficiencies in its radiation protection program. Members of the commission will now consider whether the incidents warrant further enforcement action toward Oncology Services. The company will be required to detail actions it is taking to correct its radiation protection program to the NRC. The agency will reinspect Oncology Services before it reinstates the firm's license. At a Feb. 8 meeting of the NRC's commissioners, NRC investigators released a report on their investigation of the Oncology Services incidents and summarized their findings. Among the investigation team's conclusions is that "weaknesses existed in the design and testing of the Omnitron...system and its source wire," the report states. The investigators noted that the Omnitron device currently does not verify the physical length of the source wire that returns to the machine after treatment. Instead, the NRC investigators claim that the machine checks the wire length by "comparing the wire position when the home sensor is activated during extension to the position when the home sensor is deactivated during retraction." In addition, while "any source wire length errors are reported to the operator at the main console and will cause a manual retract alarm to sound" during a normal treatment sequence, "when the emergency dc retract motor is activated, all optical detection mechanisms disengage, and source wire length information is lost," the report states. The investigators note that during the overdose incident in November, the emergency mode was engaged to retract the source wire. The NRC report says that the wire breakage may be due to the fact that in some Omnitron devices, the cavity in the wire that contains the radiation source "was off center through various portions of the wire." Also, the investigators note that Omnitron has found that the nickel-titanium wires may become brittle when the Teflon lining the containers used to transport them breaks down in the presence of moisture and forms hydrofluoric acid. The team adds that "the potential root cause of the source wire breaks was weaknesses in design validation" of the wires. Omnitron stopped shipping wires in the Teflon-lined containers on Nov. 1 because the wire tips were shaving off pieces of the material and creating dust in the containers. After the wire breakage incidents, the company asked customers to return wires transported in Teflon so that they could be replaced with wires shipped in stainless steel. The effort was complete by Dec. 20, according to the firm. FDA has completed good manufacturing practices inspections of Omnitron and issued a FD483 list of observations to the firm on Jan. 11. Omnitron says it responded to the 483 on Feb. 1 and currently is implementing changes to its GMP program in order to achieve compliance. The NRC investigators' report says that the Oncology Services/Omnitron incidents demonstrate that the intersection of FDA and NRC authority over radiation therapy devices "is poorly defined." At the Feb. 8 briefing, Commissioner James Curtiss stressed the need for "further follow up on our relationship with the FDA." The report also concludes that NRC's program for "regulatory oversight of HDR after-loader users" has weaknesses because "HDR is not addressed specifically" in many regulations and guidance documents, and "licensing guidance for HDR has been unchanged since 1986 in spite of significant changes in medical regulations and other medical licensing guidance." While using these documents to perform licensing inspections in the field, "some experienced NRC staff...were confused over the applicability of some [requirements] to HDR" systems, the report says. At the briefing, Commission Chairman Ivan Selin said that HDR therapy devices seem "to fall between a gap in our regulations." The commissioners concluded that the investigators' observations should be considered as part of NRC's ongoing evaluation of the nuclear medicine regulation program. The NRC commissioners will be briefed on potential changes to the program at a Feb. 22 meeting in Washington, D.C.
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