Photon dose calculations in homogeneous media for a treatment planning system using a collapsed cone superposition convolution algorithm

This work reports on some of the initial tests that were conducted during the commissioning of a commercially available 3D treatment planning system. The system (Pinnacle 3.0d-u1) uses a collapsed cone implementation of the superposition convolution algorithm. Calculated and measured dose in homogeneous media were compared for wedged and unwedged fields for both symmetric and asymmetric collimator settings. Results show agreement of 2% or 2 mm in most cases. Where larger differences were found, further investigation was undertaken to explain these differences. These tests demonstrate the correct behaviour of the collapsed cone implementation of the algorithm in homogeneous media and its ability to characterize the beam.