The basic public health insurance will cover part of the costs of the treatment. There is the possibility of getting an additional insurance which will also cover extra costs during hospitalisation. It is also possible to get a private insurance.
However, you will need to pay for the bills yourself first, and your insurance will then reimburse you. If you do not have an insurance, the Openbaar Centrum voor Maatschappelijk Welzijn (OCMW) in Flanders, Centre Public d’Action Sociale (CPAS) in Wallonia can provide this service.
For more information on OCMW/CPAS: http://www.ocmw-info-cpas.be/fiche_FV_nl/les_adresses_et_heures_douverture_des_19_cpas_de_la_region_de_bruxelles_cap