Hundreds of scans are being re-examined by specialists at a Yorkshire hospital after concerns were raised about a series of significant errors.
Results of around 600 CT scans reported by a locum doctor are being checked in the exercise ordered by health bosses.
A small number of patients are said to have had their treatment changed as a result of errors uncovered.
An initial examination of 200 images indicated a significant error rate of 10 per cent in reporting of results from scans carried out between November and February, leading to the full review.
Scans of the highest risk patients have been examined first. Doctors who ordered the checks are being asked to identify any potential harm to patients, with some recalled to discuss changes to their treatment.
A full investigation into the incident involving the unnamed locum doctor is underway. The review is due to be completed by the end of the month.
A spokeswoman for York Teaching Hospital NHS Foundation Trust said: “The trust discovered some anomalies in the reporting of some CT scans by a locum consultant radiologist between November 2015 and February 2016.
“As a result, a serious incident investigation has been declared, with a full review of the scans having taken place.
“During the investigation we have established that for the vast majority of patients this has not resulted in the need to change their treatment plans.
“There are a small number of patients that we have recalled to clinic to discuss potential changes to treatment plans.”