search for Phd topic

I am an oncologist interested in research and at this point of my career i do not want to engage in research degrees for the sake of it. i hope to find a topic which can shape future research in my life. Maybe that is too much to ask for from a Phd!

The topics i have thought about either feel too big or too small for a degree .i ll list some of them here

1) Cardiac doses from lung cancer radiotherapy to redefine the dose constraints in planning in the era of systemic therapy adding to the cardiac toxicity

2) Biomarkers predicting immunotherapy failure/adverse events in lung cancer

3) Develop AI tool to understand the language of dysphasic brain tumour patients

Would appreciate any  advise