The cancer centre which gave a teenager 19 overdoses of radiation has given 39 other patients radiation overdoses in the last 20 years, the BBC has learned.
Lisa Norris received 19 radiation overdoses at the Beatson
The mistakes were discovered by another cancer patient under the Freedom of Information Act.
An inquiry is still under way into why 15-year-old Lisa Norris was given 19 overdoses at the Beatson Oncology Centre in Glasgow.
A health board spokeswoman said only Lisa's case warranted a full inquiry.
The overdoses given to the teenager in January 2006 left her with burned skin and in constant pain.
After a series of pioneering treatments in a hyperbaric chamber in Dundee to try to reduce the effects of the overdose, she has now returned home but her long term health is uncertain.
In the wake of Lisa's case, the Beatson's medical director, Alan Rodger, assured the public that "no other patient treatments have been compromised".
However, Katharine Tylko, who runs a cancer support group in Bath, Somerset, discovered there have been another 44 serious mistakes at the Beatson involving radiotherapy, of which 39 were overdoses.
Most involved levels of radiation which had to be reported to the Scottish Executive because they were classed as "'much greater than intended."
The Greater Glasgow Health Board admitted there had been 46 serious incidents since 1985.
A total of 45 took place at the Beatson. One other was at the HCI hospital in Clydebank before it was bought by the NHS.
A spokeswoman for NHS Greater Glasgow and Clyde told BBC Scotland: "Since 1985, around 29,000 courses of treatment have been provided to patients attending the Beatson Oncology Centre."
There were 44 serious radiotherapy incidents at the Beatson
She said that of those, 46 incidents occurred in which the treatment given was "different than planned" and were required to be reported.
"As soon as these incidents were identified, consideration was given as to whether to continue or stop further radiation treatment," she said.
"In all but 12 of the incidents over a 20-year period, treatment continued because the probability of the benefits of tumour control or cure significantly outweighed any potential side effects of radiotherapy."
She added that in all such incidents, patients would be informed.
In a letter to Mrs Tylko, the health board said the majority of cases had no adverse effect on the outcome of treatment.
It said incidents such as the one involving Lisa were rare in comparison to the thousands of patients who were treated every year.
However, Mrs Tylko is calling for a better monitoring system so that lessons are learned from every mistake.
She has been compiling a list of all the serious accidents involving radiotherapy in the UK and has discovered that more than 200 cancer sufferers have been seriously injured or killed by overdoses of radiation in the last six years alone.
Mrs Tylko said a report into a major incident in West Yorkshire in 2004 was never circulated to other radiotherapy centres and believes the majority of accidents are caused by poor working conditions, including staff shortages and poorly maintained equipment.
Last year the Beatson, Scotland's largest cancer treatment centre, dealt with 6,758 patients.