United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-54: Teletherapy Unit Malfunction

                                                            SSINS No.: 6835 
                                                            IN 85-54       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                July 15, 1985

Information Notice No. 85-54:   TELETHERAPY UNIT MALFUNCTION 

Addressees: 

All NRC licensees authorized to use teletherapy units. 

Purpose: 

This information notice is intended to alert users of teletherapy units of a 
recent incident involving an Atomic Energy of Canada Limited (AECL) 
Theratron 60 unit. It is expected that licensees will review the information
for applicability to their facilities and consider actions, if appropriate, 
to preclude a similar problem occurring at their facilities. However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Description of Circumstances: 

A pressure regulator switch (Sl5) on the pneumatic system to an AECL 
Theratron 60 teletherapy unit failed. As a result, the compressor in the 
unit continued to run causing an overpressure condition in the holding tank. 
This condition prevented the source drawer from immediately closing on 
command. 

After treating a patient, the operator noticed that the compressor kept 
running and that there was an unusual odor at the back of the machine. The 
machine was then turned off. The operator notified management, but no 
maintenance was ordered at the time. When more patients arrived, the machine
was turned back on and the treatments continued. After several patients had 
been treated, the teletherapy unit failed to automatically return its 
cobalt-60 sealed source to the shielded position. The operator observed that
the indicator light on the radiation monitor in the treatment room remained 
on after the unit timer reached its zero setting. Attempts to turn off the 
Unit by using the console controls failed. The operator immediately removed 
the patient from the treatment room. The pneumatically operated source 
drawer independently returned to the closed position approximately an hour 
later. 

Discussion: 

An AECL representative has evaluated the incident and has concluded that 
this is an isolated incident resulting from a failure to follow prescribed 
maintenance 



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                                                              IN 85-54     
                                                              July 15, 1985 
                                                              Page 2 of 2  

procedures on the unit. In this case, prompt emergency response by licensee 
personnel to remove the patient from the treatment room after the failure 
rather than continue efforts to return the source to the "off" position 
avoided unnecessary radiation exposure. 

No specific action or written response is required by this information 
notice. If you have any questions regarding this matter, please contact the 
Regional Administrator of the appropriate NRC regional office or this 
office. 


                                   James G. Partlow, Director 
                                   Division of Inspection Programs 
                                   Office of Inspection and Enforcement 

Technical Contact:  H. Karagiannis, IE
                    (301) 492-9655

Attachment: List of Recently Issued IE Information Notices
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