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The use of ionizing radiation (IR) for medical diagnosis and treatment has had a significant impact on the survival of patients. Although the benefits of these techniques lead to successful health care, evaluation of potential associated long-term adverse effects is required. Radiation epidemiology aims to investigate the effects of IR on humans for establishing radiation protection standards and effective implementation of public health strategies. Much of our understanding of the radiation effects and appropriate radiation protection were originally based on data from the Life Span Study (LSS) of Japanese atomic bomb survivors, which however, was a specific population exposed to conditions that differ from medical settings. It is therefore, essential to complement the existing studies by following-up medically exposed population to provide a better estimation of risk.

Diagnostic procedures represent the first source of exposure to man-made radiation among the general population with computed tomography (CT) being the main contributor. CT typically delivers doses substantially greater than those received from conventional radiological examinations. The growing use of CT procedures in children and adolescents is, therefore, a topic of concern. Several cohort studies on cancer effects of CT exposure in childhood and adolescence showed an increased risk of leukaemia and brain tumours. Recently, the first results of the large EPI-CT study, including about 1 million young CT patients from 9 European countries, added evidence of an increased risk of brain cancer following low-dose exposure. Also important are the follow-up studies of childhood cancer survivors, including patients treated with radiotherapy and other anti-cancer treatment modalities, who have been followed since the 1970s for various health outcomes.

The HARMONIC project aims to complement existing studies on the effects of exposure to IR by improving the understanding on exposed paediatric patients in cardiological and oncology settings. It addresses exposure to a wide range of doses of photons, protons, and secondary neutrons due to their treatments. The cardiology component is devoted to further investigating risk of cancer based on analyses of data from a large cohort of young patients treated in 7 European countries.  The radiotherapy part of the project aims at establishing the first European registry of paediatric patients treated with modern radiotherapy techniques to investigate late cancer and non-cancer effects (endocrine dysfunctions, cardiovascular diseases, neurovascular damages and Health-related Quality of Life). Results will therefore contribute to updating the scientific knowledge based on contemporary data on interventional cardiology and radiotherapy.

The MEDIRAD project, in turn, was devoted to enhance the scientific basis and clinical practice of radiation protection in the medical field, and included a work package devoted to 2 complementary aspects of the EPI-CT study: a follow-up of the EPI-CT cohorts in 4 countries to improve the statistical power for direct estimation of cancer risk compared to already published results and a nested-case control study to estimate haematological and brain cancers risk from paediatric CT exposure assessing the influence of potential confounding factors or individual susceptibility modifiers. MEDIRAD also included several aspects of radiation protection in medicine: dose optimization in CT scanning, multimodality imaging and fluoroscopy guided interventions, impact of low-dose exposure from radioiodine therapy for thyroid cancer and breast radiotherapy and secondary cardiovascular risks. It published a series of recommendations, which will be discussed.  

The reliability and precision of epidemiological study results strongly depend on the accuracy of radiation dose estimates. Within the two projects (MEDIRAD and HARMONIC), substantial effort was devoted to improving patient-specific organ dose estimation and assessing the associated uncertainties using archived dosimetry data and developing Monte-Carlo and analytical tools based on anatomically-realistic computational phantom models.

The two projects are therefore very complementary with regard to exposure scenarios and scientific approaches to contribute to further investigating the health effects of paediatric exposure to ionizing radiation.