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On the Use of a Diode Array for the Commissioning of Dynamically-Wedged Asymmetric Fields Generated by Varian EDW's in the Pinnacle Treatment Planning System

M Ahmad

M Ahmad1,2,3, *, W Liu1,2,3, J Deng1,2, K Nguyen2,3, D Wu2,3, Z Chen1,2, M Moran1,2, R Nath1, (1) Yale School of Medicine, New Haven, CT, (2) Yale-New Haven Hospital, New Haven, CT, (3) The William W. Backus Hospital, Norwich, CT

SU-E-T-289 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To present a validation study of enhanced dynamic wedges (EDWs) implemented into Pinnacle3 treatment planning system (TPS) using a diode array, Monte Carlo (MC) simulation, and measurements.

Method and Materials: Modeling of EDW dose distribution in the Pinnacle3 TPS is based on a combination of open-field beam data and the Varian 'Golden Segmented Treatment Table' (GSTT) unique to each photon beam. To validate the EDW models, dose profiles of 6- and 10-MV photon beams from a Clinac 2100C/D were measured in virtual water at depths from near-surface to 30 cm for a wide range of asymmetric field sizes and wedge angles using the Profiler-2 diode array system. The EDW output factors for asymmetric fields were measured in solid water using a small-volume cylindrical ionization chamber placed at a depth of 10 cm on the central axis. In addition, absolute doses on central axis at depths of 5, 10, 15 and 20 cm were measured in virtual water using a small-volume cylindrical chamber for comparison with the collapsed-cone convolution (CCC) calculations. The 6- and 10-MV photon beams emerging from the treatment head of the Clinac 2100C/D were fully simulated using the Monte Carlo code BEAMnrc and DOSXYZnrc. This code was used to calculate the central-axis percentage depth doses and dose profiles for the open and dynamically-wedged fields in a water phantom.

Results: The off-axis dose profiles of various EDWs computed with the CCC dose model and MC simulations agreed with measured EDW dose distributions to an accuracy of better than 2%/2 mm. Measured EDW output factors used for MU calculations in Pinnacle3 TPS agreed with MC predictions within 1-2%.

Conclusions: The utility of Profiler-2 diode array system to measure dose profiles for commissioning of EDWs into the Pinnacle3 TPS has been demonstrated to have acceptable accuracy for clinical implementation.

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