Pain during CT Contrast

My mother has breast cancer that has metastizied to the bone -- skull and spine.  She has been taking Arimidex since last June and in November her CA15-3 markers, which had been going down, started to rise.  Her doctor says that they must do a CT with IVcontrast to validate that the change in markers is due to the ineffectiveness of the Arimidex.

During the last CT with intravenious contrast she experienced the most terrific headpain when injected.  On a scale of 1 to 10 it felt like 50.  As a result she is afraid of having another one.  She felt like it could kill her or cause a stroke or something awful.  She has mentioned this to more than one medical person and is just told they don't know what to make of it.  She needs to know if anyone else out there has had any similar experiance or knows a reason why this might occur.  Also note that the area of headpain is also an area of cancer activity.

Because her doctor will NOT change her meds without a CT(with IV) she is now 2 months further down the road and physically clearly sicker.  But stranded between her concern over the CT(with IV) and the doctors failure to offer anything else.