Look at the upper part of this film. This is film fog. How did this happen?
Most likely, after the exposure was done, the upper part of the film was exposed to light. This probably happen in the darkroom just as the last part of the film is going into the processor. Either somebody open the door or turn on the darkroom light.
But in this case, it is a funny story. Just as the last part of the film is going into the processor, the radiographer's mobile phone rang. Automatically he picked up the phone and start talking without realising that when the phone rang, it gave out a light and this fogged the film. The lesson is - dont bring your mobile into the darkroom!