Can chemotherapy regimen lead to a change of behavior and personality by affecting your brain ?

Absolutely!: There is a diagnosis called "chemobrain". It's a real change in memory, concentration, and cognitive ability as a result of chemotherapy. No one really understands the causes, but it's likely due to the toxic effects of chemotherapy on nervous system tissue. It usually improves with time. Don't let anyone tell you it doesn't exist. It does, it's just hard to measure!