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

Abstract

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.

Comparison of monitor unit calculations performed with a 3D computerized planning system and independent “hand” calculations: Results of three years clinical experience

“…For all four treatment sites the average value of the MU ratio is near 1.01; that is, there is an average 1% difference between the treatment planning system and the “hand” monitor unit calculations. Starkschall et al 6 reported similar systematic differences of 0.5% to 1.0% using the Pinnacle 3 planning system and speculated that the discrepancy may be related to differences in the determination of the beam entry point resulting from the voxel size of the calculation grid. For our data, the standard deviation of the MU ratio is smallest for prostate at 0.5% and is greatest for breast at 1.6%, with the rectum and brain intermediate to these.…”

“…A histogram showing the distribution of MU ratios by site for Pinnacle 3 TPS compared with “hand” calculations.…”

“…The monitor units calculated using our treatment planning system, Pinnacle (ADAC Laboratories, Milpitas, CA), 3 are used for treatment delivery. Dose is prescribed to a single reference point inside the planning target volume as described by (ICRU) reports 8 …”

“…, 2 Several studies 3 , 4 , 5 have been published showing that an accuracy of $1–2\%$ can be achieved along the central axis of open or wedged beams in standard “commissioning” geometry, i.e., normal incidence to a flat phantom usually composed of water. Errors increase for more complex geometries.…”

“…Leszczynski and Dunscombe 7 concluded that for the Helax‐TMS planning system (Helax AB, Uppsala, Sweden) it is possible in typical clinical situations to corroborate the dose calculation to a reference point using a standard manual calculation method. In this paper we present a comparison of the monitor unit calculations of our planning system, Pinnacle 3 (ADAC Laboratories, Milpitas, CA), with “hand” calculations for a large number of clinical cases. The purpose was to evaluate the accuracy and utility of the “hand” calculation as a verification tool in several treatment sites covering a range of treatment complexity.…”