A good topic for a quantitative study comes out of a viable research problem and a current literature gap that entails a rigorous inquiry to address using measurable variables with a large sample size. Therefore, you could read recently published studies on your area of interest and concentrate on suggestions for further investigation, which can help you zero in on an interesting researchable topic. For germane guidance, you could refer to Chapter 7 of Thomas’s (2021) book, fully cited below.
Thomas, C. G. (2021). Research methodology and scientific writing. Springer International Publishing. https://doi.org/10.1007/978-3-030-64865-7
Considering your medical research background, it is suggested to work on those topics that demand accuracy especially in diagnostics and management in any specific medical field (especially genetics, pathology, molecular biology, etc.).
Going through literature and working out a research question would help at first.