SU‐E‐T‐463: Utilizing the TG119 Assessment to Quantify Planning System Improvements

Abstract

Purpose: To quantify the impact of modifications to an IMRT planning system using the TG1 19 assessment score as an indicator of improvement. Method and Materials: Evaluation of an IMRT system following the TG1 19 protocol was initially performed to establish baseline results. The TG1 19 evaluation set consisted of five IMRT test cases planned and delivered to a 30 cm × 30 cm × 15 cm solid water phantom. Per‐field measurements were collected using a diode array, and composite measurements were collected using film and an ionization chamber. Measurements were compared to calculation to determine TG1 19 confidence limits. The original plans were then modified to include table attenuation, previously omitted by the planning system. Without modifying the incident radiation fields, the plans were recalculated on the modified phantom, which includes a table model. The resultant calculations were compared to the original measurements, and new TG1 19 confidence limits were determined. Results: The baseline TG1 19 assessment resulted in confidence limits of 4.36%, 23.8% and 9.16% for diode array, composite film, and composite ion chamber measurements, respectively. The TG1 19 assessment after plan modification resulted in confidence limits of 4.36%, 19.5%, and 8.54%. The TG1 19 confidence limits were reduced by 4.30% and 0.62% in film and ion chamber, respectively, which is a relative improvement of 18.1% and 6.8%. Conclusions: Using a single set of measurements, modifications to the planning system via the addition of a table model resulted in quantifiable improvement in TG1 19 assessment results. In this system, the addition of a table model improved the agreement between calculation and measurement, as indicated by the TG1 19 confidence limit results. The improvement was only observed in confidence limits from composite comparisons using film and ion chamber, but not observed for per‐field comparisons using a diode array.