Siemens Mevatron MD2 Medical Charged-Particle Radiation Therapy System; (Interlock #51 Jaw Field Position) Model Number: 09401654, Siemens Medical Solutions, Concord, CA 94520

Incorrect field size -- Products manufactured prior to 1999 may experience jaw field size errors during interlock resulting in potential mistreatment if a light field check is not performed. This problem is present in machines with serial numbers less than 3094, as they do not contain redundant sensors for jaw position.

The firm has sent consignees a Customer Safety Advisory Notice on August 7, 2007 informing them that a misplacement of the X and/or Y jaws can occur if interlock #51 Jaw Field Position is asserted and then cleared with the left-hand key rest. The firm recommends that if an interlock issue is encountered tha treatment of the patient be discontined until this issue is resolved.