Research with cancer registry data in radiation oncology-current possibilities and perspectives : A narrative review

Cancer registry data are an essential resource for population-based oncology research and quality assurance in Germany. With the revision of the Federal Cancer Registry Data Act in 2021, for the first time, a legal basis was created for the development of a nationwide clinical cancer dataset. This registry offers new opportunities for research, particularly in radiation oncology.

This review aims to provide an overview of the current possibilities of and challenges to using German cancer registry data in radiation oncology, with a focus on data structure, missing data, access procedures, and methodological aspects for scientific research.

We examined legal frameworks, data access procedures, and the structure of the nationwide basic oncology dataset (oBDS), particularly the components relevant to radiotherapy (RT). The completeness and comprehensiveness of RT data across federal states were assessed using national registry data from the German Center for Cancer Registry Data (ZfKD) for the years 2020-2022.

The cancer registries provide structured data on RT through the oBDS, including treatment intent, technique, target area, and side effects. However, significant variability in terms of completeness and reporting standards persists among federal states. Missing data rates remain high in some regions, particularly for key RT parameters such as treatment technique, the relationship to surgery, and boost application. Methodological challenges for scientific use include handling missing data, confounding, immortal time bias, and exposure misclassification.

Despite existing limitations, cancer registry data in Germany represent a valuable resource for real-world research in radiation oncology. They allow for large-scale population-based studies beyond the constraints of clinical trials. With improved data harmonization, methodological rigor, and future data linkages (e.g., to health insurance data), registry-based studies can contribute significantly to evidence-based decision-making and quality improvement in radiation oncology.