Children who had radiotherapy that exposed their pancreas to radiation are almost three times more likely to develop diabetes in later life, claims a study published online today in The Lancet Oncology.
Researchers analysed 2,520 patient questionnaires and medical records from French and British people who had cancer in childhood but survived for at least 20 years after undergoing treatment.
Using modelling techniques and information about how the patient would have been likely to be treated when they received radiotherapy, the researchers managed to reconstruct exactly how and where the respondents were exposed to radiation when treated.
Overall, at age 45, 2.3% patients who had not received radiotherapy had been diagnosed with diabetes, compared with 6.6% of those people who had been treated for childhood cancer with radiotherapy.
The researchers calculated that when the tail of the pancreas was exposed to radiation, patients were significantly more likely to be diagnosed with diabetes later in life, although radiation exposure to other parts of the pancreas did not affect diabetes rates.
The authors speculated that this was because the tail of the pancreas contains a type of cell involved in insulin production.
The level of radiation given to a child was also relevant and they found that higher doses of radiation resulted in a greater likelihood of acquiring diabetes in later life.
Patients who received an average radiation dose of 24.2 Grays to the tail of the pancreas were 12.6 times more likely to be diagnosed with diabetes within 20 years of completing radiation therapy, compared to patients who did not receive radiation therapy.
The type of cancer treated also affected later diabetes risk. Analysis of the data showed 14.7% of patients who had been treated for kidney cancer had been diagnosed with diabetes by age 45, compared to an average of 3.1% for other types of cancer included in the study.
Radiation therapy for kidney cancer most often focuses on the abdominal area, which would increase the likelihood of the tail of the pancreas being exposed to radiation.
One of the authors Dr Florent de Vathaire of the Centre for Epidemiology and Public Health of INSERM at the Gustave Roussy Institute in France, said: “The pancreas needs to be regarded as a critical organ when planning radiation therapy, particularly in children.
“Until now, the pancreas was one of the few organs not considered at risk of normal tissue complication in the French and the UK national guidelines for cancer radiation therapy. Our findings indicate that the pancreas is an organ at risk during radiation therapy and has to be contoured when planning treatment, to ensure a radiation dose of as low as possible.”
In a linked comment in the journal, Kevin Oeffinger of the Memorial Sloan-Kettering Cancer Center, New York, said: “The clinical implications of this study are important, since radiation remains an integral part of therapy for many children with Wilms’ tumour or neuroblastoma.
“Diabetes is a major risk factor for all-cause and cardiovascular mortality. Further study is therefore needed to clarify the mechanisms underlying diabetes after abdominal radiation.”