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  4. Investigation of 3D Gamma Analysis for Small Field Treatments

Investigation of 3D Gamma Analysis for Small Field Treatments

Y Wang1*, C Velten2 , P Black3 , J Adamovics4 , C Wuu5 (1) Columbia University Medical Center, New York, New York (2) Columbia University Medical Center, New York, New York (3) Columbia University Medical Center, New York, New York (4) Rider University, Lawrenceville, NJ, (5) Columbia University Medical Center, New York, New York

Presentations

(Sunday, 7/29/2018) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 4

Purpose: Stereotactic Radiosurgery utilizes precise patient positioning and a higher single radiation dose fraction delivered to a focused area. However, due to the small treatment fields with highly irregular and steep dose gradients, it is challenging to perform patient specific quality assurance (PSQA) using conventional methods, such as two-dimensional (2D) diode arrays. EBT3 films with submillimeter resolution have been used to resolve this problem. In this study, the feasibility of using PRESAGE 3D dosimeter (Heuris Inc.) to measure small-field dosimetry was investigated. In addition, 2D gamma analysis at different depths was evaluated using 3D information provided by PRESAGE.

Methods: To investigate the small-field dosimetry capability of 3D PRESAGE dosimeters, field sizes of 6, 8, 10, 12 mm defined by MLC and jaws were delivered to a dosimeter by TrueBeam (Varian Inc.) for beam profiles and output factors measurements. After irradiation, the dosimeter was scanned using a parallel beam optical CT scanner with submillimeter resolution and 1200 projections. The results were compared with EBT3 films and microDiamond detector. In addition, the verification plan of a clinical small-field treatment for spinal metastasis was delivered to the 3D dosimeter to conduct 2D gamma analysis at different depths. The results can provide additional information to aid small-field plan acceptance judgment and evaluate the 2D gamma test currently used.

Results: In beam profile comparison, the measured penumbra and FWHM by PRESAGE agree with film within 2%. Moreover, output factors measured from PRESAGE corresponds to those measured by microDiamond with error smaller than 1% for measured field sizes. This study shows that the 3D PRESAGE dosimeter can be used to measure dose distribution as accurate as film and provide more information for PSQA.

Conclusion: This study demonstrates the small-field dosimetry capabilities of the 3D dosimeter and provides additional information on 2D gamma analysis at different depths.

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