As with any good question, the answer is, it depends. Several factors would impact this decision - specifically the time frame - has it been a very short interval or long? I would at least ask the question if the relapse is SOLELY local-regional (i.e., no evidence of recurrence outside of the chest ...

This is a rare clinical scenario, but if confirmed recurrence pathologically and no distant metastatic disease, repeat chemoRT can be considered.  The main issue boils down to feasibility - I agree with discussing with your local Rad Onc regarding this. SCLC frequently has more central diseas...

An unfortunate situation but unfortunately, most patients do relapse even after definitive therapy. I think there is a "could you" aspect and a "should you" aspect. Can you repeat chemoradiation? This is more of a safety question and it largely depends on the location, the underlying lung function, ...