United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 76-08: Teletherapy Units


                          WASHINGTON, D. C. 20555 

IE Bulletin No. 76-08 Date: August 9, 1976 



A recent investigation by the Nuclear Regulatory Commission (NRC) indicates 
that some NRC-licensed teletherapy units may be operated in such a manner as
to deliver a radiation output which differs, outside of acceptable limits, 
from the calculated output used as a basis for administering the dose 
prescribed by the physician. 

The NRC investigation of the use of a cobalt-60 teletherapy unit at the 
Riverside Methodist Hospital, Columbus, Ohio revealed that during the period
March 1975 through January 1976, the delivered dose from the teletherapy 
unit was at variance with the medically prescribed dose. The investigation 
showed that in this case these variances were due to human error in the 
calculation of the radiation output as derived from a calibration of the 
teletherapy unit and not due to malfunction of the equipment. The Riverside 
Methodist Hospital took prompt corrective action when this situation was 
identified. In considering this situation, NRC also reviewed preliminary 
results from a study which compared the measured radiation 


output with the calculated radiation output of some cobalt-60 units. These 
preliminary results show that for a fraction of the comparisons made, there 
are variances outside of acceptable limits between the measured and the 
calculated output. 

In implementing its licensing and inspection procedures the NRC has expected
that teletherapy machines are calibrated in accordance with accepted 
standards of practice. In view of the current information, however, timely 
action by licensees is necessary to obtain assurance that NRC-licensed 
teletherapy units will deliver the radiation dose prescribed by the 


All licensees currently authorized by NRC to possess NRC-licensed 
radioactive material in teletherapy devices for human therapy are requested 

     1.   Measure the radiation output (exposure rate or dose rate) from 
          each teletherapy unit under one typical set of machine operating 

     2.   Compare the measurements obtained in Item 1, above, with the 
          calculated output values used as a basis for administering 
          prescribed doses (such as the calculated values from the physical 
          decay of the radioactive source since the last full calibration). 


     3.   If the measured output obtained in Item 1 differs from the 
          calculated output by more than 5%, perform a full calibration of 
          the teletherapy unit in accordance with accepted standards of 
          practice, such as those recoffnended by the Scientific Committee 
          on Radiation Dosimetry of the American Association of Physicists 
          in Medicine. (Physics in Medicine and Biology, Vol. 16, No. 3, 
          1971, pp. 379-396)  

     4.   Report the completion of the requested action and a summary 
          description of the methods used. These reports, which may be 
          released to the public under the Freedom of Information Act, are 
          requested to be submitted within 30 days after receipt of this 
          bulletin to the Director, Division of Materials Inspection 
          Programs, Office of Inspection and Enforcement, USNRC, Washington,
          D. C. 20555; a copy of the report should be sent to the Director 
          of the appropriate NRC Regional Office listed in Appendix D, Title
          10, Code of Federal Regulations, Part 20, or on Form NRC-3. Any 
          questions concerning the instructions in this bulletin should be 
          directed to the appropriate NRC Regional Office. 

     5.   As an alternative to the actions described in Items 1, 2, and 3, 
          above, licensees who participate in a program of national 
          recognition that independently evaluates the output 


          of teletherapy units may submit, at their option, as the report of
          Item 4, above, copies of documents showing the results of their 
          participation witbin the past six months. The programs for which 
          this alternative is acceptable are (a) the National Bureau of 
          Standards - Bureau of Radiological Health voluntary cobalt-60 
          measurement assessment program; (b) the Centers for Radiological 
          Physics programs which are sponsored by the National Cancer 
          Institute; and (c) the Radiological Physics Center program which 
          is sponsored by the American Association of Physicists in 

Based on a review of the reports and documents submitted, licensees may be 
required to participate in an NRC-sponsored program to evaluate the 
radiation output of NRC-licensed teletherapy units. Licensees will be 
individually contacted as appropriate. 

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U.S.C. 3152 from the U. S. General 
Accounting Office. (GAO Approval B-180255 (R0072), Expires 7/31/77.)  

                                   Dudley Thompson, Acting Director 
                                   Division of Field Operations 
                                   Office of Inspection and Enforcement 
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