Varian Multileaf Collimator [MLC]; Millenium Multileaf Collimator [52, 80, 120 leaf]; High Definition 120 Multileaf Collimator Model Number(s): product code: H54 and H56; MLC software version 8.5 - Product Usage: is intended to assist the clinician in the delivery of external beam radiation to defined target volumes during radiosurgery and radiotherapy while sparing surrounding normal tissue and critical organs from excess radiation.

After a recent upgrade to the collimator software version 8.5, the firm became aware that the multi-leaf collimator leaves did not move during an arc treatment. The issue is related to a transient carriage primary- secondary interlock due to carriage fault on the MLC that immediately preceded the initiation of the arc treatment. The issue will occur only with MLC software version 8.5 and only affects conformal arc treatments, including VMAT and RapidArc. There have been no reports of adverse health consequences due to this issue.

Urgent Medical Device Correction Field Safety Notice letters were sent to customer beginning August 12, 2019. Letters were sent to U.S. and Canadian customers via Fed-Ex, and via local third-party courier or email for the rest of the world. Users were instructed to: 1. monitor MLC leaf movement on the 4DITC console screen, 2. observe the start of every arc treatment and verify that the leaves are moving as intended, and 3. stop treatment immediately if MLC leaves are not moving and contact Varian to assess the MLC status. Users may contact Varian Support for help to verify whether carriage faults have been recorded for the MLC. If carriage fault is confirmed in the TerminalLog file, users were instructed to contact Varian Service Representative to assess the MLC status. Customers were requested to complete and return the response form provided to [email protected], and to contact their local Varian Medical Systems service manager with any questions. The notification letter includes Varian Support Information with the following contact information: phone number for North America Customers: 1 888.827.4265; Global email address [email protected]; and website contact address for customers outside of North America: https://www.myvarian.com/s/contactus?lang=en.