SU-E-T-726: The Analysis of Different Percentage Depth Dose Curves Used for Commissioning in Eclipse

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Abstract

Purpose:

Percentage Depth Doses (PDDs) used for balance fitting of the calculation model in Eclipse. The effect of PDD curves measured with two different detectors for the commissioning of Truebeam STx machine to the improvement of the quality of the algorithm configuration is analysed.

Methods:

The measurement of open field PDD for 2×2cm2 to 40×40cm2 field sizes were done with two different detector types. The scan was made using 0.125cc semiflex thimble ionization chamber (PTW TM31010) and PTW 60019 microDiamond with 0.004mm3 sensitive volume. Two different machines were created in Eclipse with the same beam data except for PDD measured with two different detector types. A single 6 FFF beam with zero gantry and collimator angles for 2×2, 3×3, 5×5cm2 field sizes were planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm using two different machine created. PDD measurements were made in a RW3 solid water phantom using EBT3 Gafchromic film extending from surface to 30cm. The gamma index analysis of measured and calculated PDD curves were compared.

Result:

For the plan made using machine configured with semiflex measured PDD curves, the measured and the calculated dose distributions for 2×2cm2 field size gamma analysis passing rate was 97.6% within 2% dose difference and 2mm distance-to-agreement. For the plan made using machine configured with microDiamond measured PDD curves had 98.1% passing rate for ±2% in field but the passing rates. Passing rates were increasing with the field sizes. For 5×5cm2 field size they are 98.3% and 99.1% respectively.

Conclusion:

The agrement with treatment planning system and measurement was better when fine resolution detector was used especially for small field sizes.

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