Invoices show off-site medical imaging provider Everlight has been tasked with more work in the first three months of this year than all of 2018.

The use of the company to read CT scans and X-rays has proved controversial, with multiple hospital heads slamming the practice - which according to invoices became commonplace at Canberra Hospital in 2017 - as putting patients at risk.

But the hospital says it is necessary to cover unplanned leave and staff vacancies.

Government invoices show Canberra Hospital spent $1,290,586 on Everlight in 2018.

As of March 2019, it had already spent $1,526,449.20 in 2019.

In 2017, the government spent $585,448.60 on the services over the whole year.

There were no invoices paid to Everlight in 2016, while $112,898.50 was paid in 2015.

Doctors and medical groups have expressed concern at the ongoing use of the off-site reading of scans, which sees doctors interstate or overseas reviewing scans.

This is instead of being reviewed by a doctor in the hospital who has access to the patient, other treating doctors and the patient's previous scans.

A Canberra Health Services spokesman said off-site radiology service was an important strategy in many hospitals.

"It ensures the continuity of high-quality, efficient care for our patients at times such as after hours and when unplanned leave arises," he said.

Emails obtained by The Canberra Times last year showed the clinical director and deputy director of neonatology, the clinical head of radiology and the clinical head of oncology all raised serious concerns about the use of off-site reporting and the implications for patient safety.

In the emails, the head of oncology cited a case where an urgent diagnoses was missed for days due to delays getting reports back from Everlight.

The spokesman said its expenditure with Everlight had jumped this year due to increased workload and current radiologist vacancies.

"Canberra Health Services is continuing to recruit additional radiologists and this will greatly reduce the need to use external agencies as additional radiologists commence," he said.

He said the reading of some CT scans and X-rays was being done off-site when the situation arose.

It comes as three radiologists pursue the hospital claiming it took retaliatory action against them when they made protected disclosures about patient safety and administration of the medical imaging department.

In a preliminary hearing in the ACT Supreme Court, the hospital was ordered to hand over internal documents to the whistle-blower doctors who are looking to sue.

The Australian Medical Association said this situation had led to staff shortages and pressure on radiologists in the hospital, urging a quick resolution of the dispute.

The spokesman said two new radiologists started earlier this year at the hospital.

One radiologist was recruited in 2019 as a locum while three additional radiologists are due to start in July or August.

He said the hospital was also searching for more radiologists and a locum radiographer.

"All radiologists, as with any other [hospital] staff member, are entitled to regular leave as per enterprise agreements and legislation such as annual leave," the spokesman said.