These are three separate fields.
Radiation oncologists are physicians that provide radiation treatment typically for people with cancer (but there are other conditions that can be treated with radiation).
Interventional radiologists treat patients by passing catheters through the skin and into vessels to diagnose and/or treat disease. Common procedures include angiography, embolization, inserting stents and lines. The position of the catheters or lines are visualized using X-ray, CT, MRI, ultrasound, etc.
Nuclear radiologists perform diagnostic imaging (like a diagnostic radiologist) but the imaging is performed after the patient has been injected with radionuclides that emit radiation.
The typical pathway to interventional and nuclear radiology are through fellowships after completion of a diagnostic radiology residency. Radiation oncology is separate field that has its own residency.
