SU-E-T-725: The Analysis of Different Diagonal Profiles Used for Commissioning in Eclipse

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Abstract

Purpose:

The effect of diagonal profiles measured with different types of detectors to the improvement of the quality of the algorithm configuration is analysed.

Methods:

For commissioning of Truebeam STx machine, Eclipse requires a diagonal profiles of the largest field size. The left side of the beam profile with 5cm overscan at depths of 30cm for a 40×40cm2 field at 100cm SSD was scanned. The scan was made using PTW 0.125cc semiflex ionization chamber and PTW microDiamond with 0.004mm3 sensitive volume. Two different machnines were created in Eclipse with the same beam data except for diagonal profiles. A single 6 FFF beam with zero gantry and collimator angle for 10×10cm2 field size was planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm. Dose profile measurements were made in a RW3 solid water phantom at depths of 5, 10, 15cm using EBT3 Gafchromic film extending from field edge up to 15cm. The gamma index analysis of measured and calculated dose profiles were compared.

Result:

For the plan using semiflex configured machine, the measured and the calculated dose distributions gamma analysis passing rate was 98.1% within ±2% dose difference and ±2mm distance-to-agreement for in field doses. However they decreases to 96.8% for out of field doses. For the plan using microDiamond configured machine had 98.9% passing rate for ±2% in field but it decreases to 97.6% for out of field doses. Although passing rates were increasing with the depth for in field doses they were decreasing with depth for out of field doses.

Conclusion:

Diagonal profiles are used for source configuration in Eclipse. Because of that it can be advisable to use fine resolution detector.

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