The documents show two lifesaving linear accelerators - used to treat patients with radiation therapy - were not replaced until years after they exceeded their useful life due to funding priorities.

By this time they were no longer eligible for Commonwealth funding, sometimes unable to perform the latest treatments and prone to faults.

The latest available national data, from 2017-18, showed Canberra was already the worst performing jurisdiction for radiation oncology wait times by a significant margin.

When the replacement of the two aging machines began earlier this year, it meant the hospital was placed under further strain with the process meaning it would be down a machine until next year.

Staff have been battling to make sure its poor wait times don't get any worse in that time.

Internal correspondence obtained through freedom of information showed patients were being sent interstate for treatment due to the delays which were labelled "unacceptable" by a senior specialist.

In response to a company wide email from CEO Bernadette McDonald, sent in April, saying there had been no negative impact from one machine being down, senior staff specialist Dr Shivakumar Gananadha said "it was news to him".

"As an oncological surgeon who treats patients with esophageal and pancreatic cancers I can say that there are significant delays in patients getting radiotherapy in a timely fashion," he said.

He said he had sent patients to Sydney, Woolongong, and Melbourne while one of his colleague's patients had to go to the Gold Coast.

"This is a recurrent theme at our gastrointestinal cancer multidisciplinary meetings and has been for over a year," he said.

"Even though some patients are now being treated in the private radiotherapy centre in Bruce it has not affected the wait times as TCH has been one less machine."

In May, he emailed again to say there was still a problem with wait times despite assurances from the hospital wait times were being kept within standards of care.

"I think it is unacceptable that patients are waiting six weeks for the start of treatment," Dr Gananadha said.

Wait time is calculated from the time the oncologist classifies the patient as ready for care to the time the patient starts treatment.

Canberra Hospital has four linear accelerators, with one replacement process finished in September and another replacement due to begin this month.

Those two machines reached end of life in 2016 and 2017 respectively, but the procurement of new ones was only approved last year, the internal documents reveal.

They also showed the ageing infrastructure meant system faults and breakdowns had been affecting the provision of radiotherapy.

A Canberra Health Services spokeswoman said planning to replace the machines began in 2014 but, due to competing priorities, funding for the associated building and ICT work was only made available for the 2019/20 year.

Two more machines are due to reach end of life in 2022. She said those machines would be replaced in 2022.

Do you know more? Contact daniella.white@canberratimes.com.au

August emails from the director of radiation therapy noted waiting time compliance was moving in the right direct but still "way off the guideline".

Weekly reports - obtained for the year up until August 8 - showed waiting times compliance rates for radical therapy sometimes dipped below 20 per cent.

The median ranged from 23 to 45 days for radical treatments, while the longest a patient was waiting was 75 days.

Asked whether wait times were within community expectations, a spokeswoman said: "We ensure each patient is fully informed of their treatment options, including wait times. Our clinicians actively manage start times for treatment to optimise clinical outcomes for each patient."

She said improvements had been made in recent months that had reduced wait times despite an increase in the number of patients being treated.

Opposition health spokeswoman Vicki Dunne said the government had shown a "treacherous" failure to plan for the needs of Canberra's cancer patients.

"The Barr Government's ongoing neglect of the health system is putting lives at risk. There are no two ways about it," she said.

"We should be planning to replace [linear accelerators] before they become obsolete not two years after the fact.

"Obviously the Barr Government has had other priorities.

"I feel for radiation therapists, doctors and nurses who have to put up with Labor's treacherous failure to provide for the health system. They go above and beyond to help patients with next to no support from the government. "