Sometimes adults with ALL are given radiotherapy to the brain to prevent leukaemia from causing problems in this part of the body later on. This is called prophylactic cranial radiotherapy. It is given because small amounts of leukaemia cells may be left in the brain and spinal cord (CNS) after chemotherapy treatment. Most chemotherapy drugs can’t get from the blood into the brain.

Small numbers of leukaemia cells won’t cause symptoms or show up on scans. So, it isn’t always possible to know if there are any left behind in the CNS. Because of this preventative treatment is offered to almost everybody with ALL who responds to chemotherapy.

Another way to prevent leukaemia cells growing in the CNS is to give chemotherapy into the fluid around the brain and spinal cord. This is called intrathecal chemotherapy. It can be given on its own or with radiotherapy. If they are given without radiotherapy higher doses of intrathecal chemotherapy are needed, so usually a combination of radiotherapy and chemotherapy is used.