Technical considerations for the use of independent collimators to achieve optimal photon field matching in...

The dose uniformity across a junction between two abutting photon fields can be optimised by creating non-divergent field edges using independent collimators. Current linear accelerator specifications for the positional accuracy of such collimators are not rigorous enough to ensure that a clinically acceptable match is produced. Confirmation of the junction dose is required prior to clinical use and additional quality assurance is necessary to ensure that the strict requirement for positional accuracy is maintained.