Prescribed total radiation dose should be administered within in a specific time-frame and delays in commencing treatment and/or unplanned interruptions in radiation delivery are unacceptable because, in certain cancer sites, treatment-time prolongation can have a deleterious effect on local tumour control, and on patient outcomes. The present review evaluated the causes of initial treatment delays as well as interruptions in the scheduled radiotherapy. The literature search highlighted a significant concern in avoiding treatment-time prolongation in head and neck, cervix, breast and lung cancer. Among the causes involved in delay in radiotherapy commencement factors such as waiting lists, lack of material and human resources, and an increase complexity in planning, simulation and verification are highlighted. Most authors recommend radiotherapy commencement as soon as possible in radical (exclusive irradiation with active tumour present) and palliative situations with a maximum delay of no more than 6 to 8 weeks in the case of adjuvant radiotherapy (post-resection) programs. Interruptions during the course of treatment include: planned unit maintenance and servicing, acute patient toxicity or unexpected malfunction of linear accelerators; this last feature has the most deleterious effect on patients as well as radiotherapy practitioners. Interruptions that impact on the programmed time-course for radiotherapy needs to be compensated-for so as assure the biological equivalence in treatment efficacy with respect to cancer site and stage.