Thousands of chest X-rays and CT scans carried out on patients in the northeast are being reviewed.
There are two reviews under way, the first involves around 4,590 patients, 6,000 chest X-rays and 50 CT scans.
The X-rays and CT scans being reviewed were carried out during 2006 and 2007.
A separate external review will examine a number of cases where patients who died of lung cancer had their diagnosis delayed because an abnormality on their chest X-ray was not spotted.
The HSE has told RTÉ News that the locum consultant radiologist at the centre of the review has not worked elsewhere in the country.
Minister for Health Mary Harney told the Dáil today that individual patients will be notified of their result as soon as their X-ray or CT scan is reviewed.
Detailed letters were posted to the patients involved yesterday.
The review is expected to take around eight weeks and patients will be sent the result of their review.
The Minister said the HSE has emphasised in its letter to patients and others that the review is for precautionary reasons.
Ms Harney said that in late 2007 it came to the attention of the HSE that a small number of patients in Our Lady of Lourdes Hospital in Drogheda and Our Lady's Hospital Navan during 2006 and 2007 had their diagnoses delayed due to an abnormality in their chest X-ray not being noted on initial examination by the radiologist.
Four patients were subsequently diagnosed with lung cancer by follow up X-rays and all had passed away.
The HSE has set up a helpline for those concerned with the review of X-rays and CT scans in a number of hospitals in the north east region.
The number is 1850 24 1850, it will operate from 10am to 6pm.
