Aggregate indicators of population exposure to ionizing radiation, such as per capita dose, are often criticized by professionals. These collective exposure indicators are criticized for failing to take into account the fact that radiation delivered for diagnostic imaging is part of medical care and must be evaluated in light of the benefits to the patient’s treatment. However, conducting studies to determine the dose received by a patient as part of their care is difficult to carry out, due to the complexity of care pathways, the duration of the studies (several years for a chronic disease), and the fact that the dose received by the patient can only be calculated retrospectively, based on radiological records. We report here on two studies that explored a specific health situation in children. One of these studies involved premature newborns admitted to a neonatal intensive care unit, and the other involved patients with cystic fibrosis. The joint reconstruction of dosimetry and the course of care required significant effort to access the original radiological records and calculate the effective dose received by the patient. These are single-center studies, and extending these results to all affected patients treated in the region would require additional studies. These studies were limited to a dosimetric evaluation of an existing practice. It is worth noting that such studies are rare in the literature. They aim to provide missing and critical information for the radiation protection of populations who are not healthy but suffer from medical conditions. (Introduction)