Weeks. Side effects of radiation may start within 2 weeks of starting tx.
It varies. Side effects from radiotherapy can be classified as acute or delayed. Acute side effects (hair loss, fatigue) usually begin during the course of radiotherapy and gradually improve in the weeks after treatment (usually a few months for hair loss). Delayed side effects are far less common and can occur months or even years after radiotherapy.
Shortly after start. Symptoms will begin pretty soon after your first treatment and will persist until after your treatment is over. They are not disabling although they are inconvenient. The worst symptoms are fatigue, weight loss, possible hair loss, nausea. Some people get none of these except the fatigue. Good luck.
Meningitis. Meningitis is an infection of the brain and a brain tumor is another problem due to a space occupying lesion in the brain - they rarely go together unless there is a postoperative infection or the patient has another source for the meningitis such as a severe sinusitis.