Journal of Medical Physics
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Year : 1998  |  Volume : 23  |  Issue : 4  |  Page : 258-261

Accidental Patient Over Exposure In A Radiation Oncology Facility



Correspondence Address:
C.E De Almeida


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Accidents with radiation therapy patients, when they happen, have a high probability of being very severe. This paper describes an accident involving the over exposure of several patients submitted to electron therapy in a linear accelerator of a University oncology center that occurred in November 1996. As a result of a frequent false flatness/symmetry (flat/sym) interlock problem with the electron beams of a Mevatron-74, the radiation technologists had autonomy to access the control panel and reset the ion chamber counts, and also to operate the machine in the non-clinical mode. Unfortunately at this particular time, the switch programming/normal (prog/normal), that is only used during maintenance and to program the physical parameters for each energy was left activated. This means that the machine has been used with the settings shown at the potentiometers; in this case the setting for photons. The electron transmission chamber was not able to handle the excess of fluence and it was only registering a saturate ion voltage value until the electronics fall-down. As result of this, several patients have received an excess of dose, reading 1840 cGy in a single session. This caused severe acute reactions and late necrosis. The lessons learned and pointed out in this paper are to be strongly considered by the radiation oncology centers, the maintenance companies, the machine manufacturers and the regulatory agencies, in promoting the adoption of comprehensive quality assurance programs as well as a clear definition of the chain of responsibilities for the staff.


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