Performance evaluation of enhancement dynamic wedge implementation in a radiotherapy treatment planning system

The authors' purpose was to verify dose distributions and monitor unit calculations for Enhanced Dynamic Wedges (EDW) in the Cadplan radiotherapy planning system. A Scanditronix diode array was used to obtain dose profiles and a cylindrical ionization chamber for point absorbed dose calculations. The measurements were performed on a Clinac 600 (6 MV) and on a Clinac 2100 C (6 and 18 MV) for representative clinical fields. Cadplan calculations for EDW are based on a photon pencil beam model, using Varian Golden Segmented Treatment Table (GSTT). For absorbed dose calculations in reference point, agreement within 1.5% was obtained for 6 MV and within 1% for 18 MV. For high dose and low dose gradient region calculations, agreement within 2.5% was obtained, in general, for all photon beams. For large dose gradient region (>30%/cm), agreement within 2 mm was found if appropriate grid size was used for all photon beams. For low dose and low dose gradient region (i.e. <7% of normalization dose), agreement within 5% (of normalization dose) is obtained for large fields (i.e.>10/spl times/10 cm/sup 2/); agreement within 3% was obtained for small fields. In conclusion Cadplan calculations for EDW are in good agreement with measurements, and they are at least as good as the hard wedge calculations arc. The difference found for low dose and low gradient region in large fields with EDW is due to the photon pencil beam algorithm used by Cadplan. The same order discrepancies are found for large fields when this model is used.