A teenage cancer patient who received a huge overdose of radiation treatment died from a recurrence of her illness, it emerged today.

The postmortem examination of 16-year-old Lisa Norris gave the cause of her death as a type of brain cancer called pineal blastoma. It made no mention of the possible effects of the excessive doses of radiation she received at the Beatson Oncology Centre, Glasgow.

In a statement issued through their solicitors, her family expressed "surprise" at the results and said they intended to pursue the matter.

"We are relieved that the postmortem has been completed, but are surprised that there is no reference on it to excessive radiation as a cause of death," the statement read. "We have instructed our solicitor to take this further."

Lisa, of Girvan, Ayrshire, received 19 overdoses of radiation, leaving her with burns on the back of her neck and head, because of an error in the planning of her treatment.

The teenager died on October 18, and her father, Ken, said he blamed the incorrect radiation treatment. She is due to be buried tomorrow.

Cameron Fyfe, the solicitor acting for the family, said he intended to get an expert to review the postmortem examination and assess whether Lisa's radiotherapy could have played any part in her death.

"The cause of death on the death certificate does not refer to the excessive radiation," Mr Fyfe said. "We are instructing a medical expert to provide a detailed report on this, and in particular whether this materially contributed to Lisa's death."

A report published last week revealed a catalogue of failings that led to the error in Lisa's radiotherapy treatment at the Beatson in January.

It said the overdose happened after an underqualified and undertrained member of staff entered a wrong number on a form.

Lisa staged a remarkable recovery from her cancer just weeks after the treatment, eventually going back to school. However, she had to return to hospital in September for surgery to drain fluid from her brain.

The Crown Office and Procurator Fiscal Service confirmed it was still investigating her death.

"The fiscal has a duty to investigate all sudden and unexplained deaths, and Lisa's death was reported to us in that respect," a spokeswoman said.