Set-up errors in patients receiving radiotherapy

Set-up errors in patients receiving radiotherapy

This study aim at analysing the set-up error of head and neck cases, treated in a vacuum formed acrylic shell with an in-house immobilisation system. Two population groups were studied, namely virtual simulated and intensity modulated radiotherapy cases.All cases were treated with the in-house immobilization system, which located centrally, but not longitudinally to the treatment couch. The IMRT cases were planned by a medical physicist and consisted of 6-9 fields of 3-4 intensity levels each. Digitally reconstructed radiographs of the 2 lateral fields and the anterior neck field for the virtual simulated cases and the 2 lateral and anterior composite fields at the same isocentre for the IMRT cases, were printed and represented the ideal patient position.Offline monitoring of couch position provides insight into setup margins and this can contribute to realistic institutional planning target volumes. Better results were obtained in the IMRT cases and this could be due to the requirement for weekly verification imaging. Lack of radiation therapist vigilance and insufficient training were most likely responsible for the individual cases with systematic variations of larger than 3 cm.