The NSW oncologist at the centre of the underdosing scandal has defended his unorthodox treatment decisions, arguing there's no evidence to suggest he harmed anyone.
Dr John Grygiel says he also believes he wasn't the only specialist prescribing significantly reduced doses of chemotherapy drugs to head and neck cancer patients at St Vincent's Hospital in Sydney.
The senior doctor faced a grilling on Tuesday as he made his first public appearance after a government review found he had given "off-protocol" doses to at least 129 patients in Sydney, and a small number of patients at hospitals in the state's central west.
Dr Grygiel said he decided on a level of chemotherapy dosage 12 years before medical guidelines were introduced in 2006.
"I explained to (my patients) that there were guidelines and I explained to them that I used lower doses," he told a NSW parliamentary inquiry examining the issue, adding that consent was always given.
There was no evidence to suggest the guideline doses would have led to a better outcome for patients, Dr Grygiel said.
"Indeed in many cases, I believe it could have had a negative impact as it would have discouraged patients from continuing treatment."
The oncologist, who has since stopped practising, told the inquiry he stood by his treatment.
"You have to realise that maybe I'm not the only person who uses those sort of doses," he said.
"I have been ... in making preparations for the HCCC (Health Care Complaints Commission) investigation asked to review 84 patients from a St Vincent's cohort, and two of those patients weren't mine."
St Vincent's Hospital's chief executive and clinicians told the inquiry on Monday that Dr Grygiel continued flat dosing until last November despite the issue coming to the attention of the hospital in June 2015.
(In flat-fixed dosing, one dose of a drug is given to all patients regardless of other factors, such as height, weight and underlying health.)
He said his superiors were made aware of his practice as early as 2006 but believed he had been exonerated after an internal hospital investigation found none of his patients had been hurt by his treatment.
Dr Grygiel said he was completely "blindsided" when the issue was exposed in a media report in February.
The director of cancer services at St Vincent's, Dr Richard Gallagher, later asked him to consider early retirement to avoid a "s*** storm", he claimed.
The medical oncologist is the only person to have lost their job over the scandal.
Dr Grygiel has filed an unfair dismissal case against the hospital.
