Results:The largest error was in the superior/inferior direction (87.7% < 3mm; 6.1% > 5mm), followed by the medial/lateral direction (76.2% < 3 mm; 0 > 5 mm) and least in the anterior/ posterior direction (91.6% < 3 mm; 0 > 5 mm). The random and systematic errors in all three directions for this patient cohort were less than 2 mm, conforming to acceptable standards of delivering safe radiotherapy. Using Stroom's margin recipe (2Σ + 0.7σ) a CTV-PTV expansion margin of 5 mm can safely be applied for this patient cohort. Conclusion:When treating patients with intracranial tumours at Groote Schuur Hospital the CTV-PTV expansion margin can safely be reduced from 1 cm to 5 mm.