being a medical imaging radiologist or a radiation therapist in HK(with PolyU degree) would be easier to immigrate to countries such as UK, New Zealand and Australia

Yes — if you mean a radiography degree, both medical imaging/diagnostic radiography and radiation therapy can support immigration, especially to the UK and Australia. Overall, diagnostic radiography is likely the safer and more flexible choice because it is a broader pathway, while radiation therapy is more specialised.

Important clarification

• “Radiologist” should not be treated as the same occupation as a radiography graduate; Australia’s official occupation list, for example, lists “Diagnostic and Interventional Radiologist” separately from “Medical Diagnostic Radiographer” .
• With a radiography background, the relevant overseas titles are more likely “diagnostic radiographer,” “medical radiographer,” “medical imaging technologist,” or “medical diagnostic radiographer” .

UK

• The UK has Skilled Worker visa routes for eligible healthcare and education jobs, and healthcare roles can have specific salary rules based on national pay scales such as the NHS .
• The UK also publishes a general list of eligible occupations and codes for the Skilled Worker visa .
• The provided evidence specifically says medical radiographers qualify for UK Skilled Worker visa sponsorship, though that source is not as authoritative as GOV.UK .
• NHS-related sources also indicate that radiographers can be among internationally sponsored healthcare roles, but this evidence is less authoritative than GOV.UK .

Australia

• Australia looks particularly favourable because the official Core Skills Occupation List includes Medical Diagnostic Radiographer, Medical Radiation Therapist, Nuclear Medicine Technologist, Sonographer, and Diagnostic and Interventional Radiologist .
• This means both diagnostic radiography and radiation therapy appear to be recognised skilled occupations for Australian migration purposes .
• A separate source describes Medical Radiation Therapist as ANZSCO 251212, but the official Australian list is the stronger evidence .

New Zealand

• Insufficient evidence from the provided sources to say confidently whether medical imaging or radiation therapy is easier for New Zealand.
• You would need to check New Zealand’s current Green List, registration requirements, and employer demand before relying on either pathway.

Which is easier?

• Diagnostic radiography / medical imaging is likely easier overall because Australia’s official list clearly includes Medical Diagnostic Radiographer and several related imaging occupations, including Nuclear Medicine Technologist and Sonographer .
• Radiation therapy is also viable, especially for Australia, but it is more specifically tied to radiation treatment work .
• For the UK, both may be possible if the role fits an eligible healthcare occupation and you secure sponsorship, but the evidence provided is stronger for medical radiographers than for radiation therapists specifically .

Practical recommendation

• If your main goal is immigration flexibility across the UK, Australia, and possibly New Zealand, choose medical imaging / diagnostic radiography.
• If you strongly prefer oncology treatment work and accept a narrower pathway, radiation therapy can still be a good option.
• Before deciding, confirm whether the specific degree is accepted for professional registration in each target country; the provided evidence does not prove degree recognition.