The Medicines and Healthcare Products Regulatory Agency (MHRA), United Kingdom posted a medical device safety alert concerning XiO Release 4.51 and higher, manufactured by IMPAC Medical Systems, Inc.
When fixed wedges are defined in Source File Maintenance, the user defines a maximum field size allowed for each wedge. This maximum field size is being ignored by the software when both fixed wedges and MLCs are present in a beam. The result is incorrect calculation and delivery of dose outside the physical extent of the wedge. The dose distribution calculated by XiO will not match the dose delivered to the patient in regions beyond the physical dimension of the wedge.
According to the Field Safety Notice, Varian, Siemens and Elekta linacs with motorized wedges will prevent delivery. However, Elekta linacs with third party fixed wedges will not prevent delivery.
XiO will calculate wedged dose in the region outside of the physical wedge and the linac will deliver open dose. The patient will receive dose that is different from the planned dose and that dose difference can exceed 5%. There is a remote probability of serious injury resulting from this issue. The problem will be resolved in a patch to XiO Release 5.10.
For details, please refer to the FDA website:
https://www.gov.uk/government/publications/safety-information-from-manufacturers-field-safety-notices/field-safety-notices-31-august-to-4-september-2015
If you are in possession of the affected products, please contact your supplier for necessary actions.
Posted on 8 September 2015