How long after a brain tumor radiotherapy will the side effects start? Are they disabling?

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.

Related Questions

How long after a brain tumor operation and radiotherapy will the side effects start?

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.