ARTISTE or ONCOR Linear Accelerators in combination with 160MLC (Multi Leaf Collimator). Linear Accelerators that may be affected are: ARTISTE MV System; ONCOR Avant Garde ONCOR Impression ONCOR Impression Plus ONCOR Expression. Manufactured by Siemens AG, Medical Solutions, Kemnath, Germany; Registered by Siemens Medical Solutions, Concord, CA. ARTISTE and ONCOR family of Linear Accelerators are used to deliver X-ray photon and electron radiation for the therapeutic treatment of cancer.

Siemens became aware of a potential safety risk related to the behavior of the 160 MLC when using the "Motion Stop" button followed by "Reset" several times during the treatment of one beam or one segment.

Siemens sent a Consumer Safety Advisory and Urgent Medical Device Correction letter to all affected customers beginning on April 15, 2011. The letter identified the product, the problem, and the action to be taken by the customer. Updated instructions for using the Motion Stop button with the 160-MLC were provided with the letter. Customers were requested to use the Motion Stop button and the corresponding reset procedure only when required. In the unlikely event that the Motion Stop button needs to be used repeatedly during treatment of the same beam or segment, customers were advised to perform an "in session resumption of the beam by selecting 'abort' at the syngo RT Therapist and then re-selecting the beam again for the remaining delivery. In this case, the beam will be re-loaded with the originally prescribed leaf positions. Please consider the already delivered dose for resumption. Customers were asked to include the Customer Advisory Notice in their LINAC System Owner Manual in chapter 'Safety Advisory Letters' where it should remain until the measures defined above were performed. Customers were asked to inform all affected personnel immediately.