It has come to our attention that one or more inspectors may have directed (or suggested to) facilities that they have their imaging phantoms modified by having the normal screw heads (which protrude above the top surface of the phantom) replaced by screws that are flush with the top surface.
Presumably this came about because DMQS has modified (or asked States to modify) phantoms used in MQSA inspections in this manner. This note is simply a reminder of why these modifications were made and why it is inappropriate to require/recommend that facilities make similar modifications.
MQSA inspectors will encounter a wide variety of x-ray units and some of these use the position of the compression paddle in the process of automatically selecting the exposure technique. When inspecting such units it is helpful to be able to bring the compression paddle down in contact with the top of the phantom. While this is not generally critical for QA purposes within a facility, it is critical for MQSA inspections of this subset of x-ray systems.
Facilities are required to make phantom images periodically to assure the relative consistency of their imaging system. In doing so it is critical that they expose the phantom reproducibly but it is not generally important that the compression paddle be in contact with the top of the phantom during exposure. In fact many facilities will make the phantom image with an acrylic disc on top of the phantom to assess contrast and this disc may protrude further above the top of the phantom than do the normal screws that secure the cover of the phantom.
Therefore, while it is important that the MQSA inspector use a phantom with flush mounted screws, it is not necessary for facilities to follow suit and it is inappropriate to require or recommend that they do so. Such a requirement or recommendation would result in unnecessary expense for the facility or the phantom supplier.