Doesn't radiation therapy increase cancer cell growth?

Not really: When given appropiately, radiation helps with local control. Keeping the tumor from recurring where it started). But yes exposure to radiation can be a cause for second cancers-( tho rare) most commonly sarcomas in the area of the radiated tissue).

Yes, it can...but: This is a phenomenon known as "accelerated repopulation." radiation biologists have taught us that we can compensate for this increased cell growth rate with various techniques: higher total doses, multiple doses per day, greater daily dose intensity and/or the use of concurrent chemotherapy.

Not necessarily : It would be extremely unlikely to occur