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Small Field Verification with a New 2D Liquid Ionization Array

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L Brualla González

L Brualla-Gonzalez1*, J Pardo-Montero2, T García-Hernández1, D González-Castaño2, A Vicedo Gonzalez1, A Pazos2, D Granero1, M Zapata2, A Gago-Arias1, J Rosello Ferrando2, F Gomez2, (1) Hospital General de Valencia.ERESA, (2) Universidade de Santiago de Compostela. Departamento de Física de Partículas

SU-E-T-63 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
A new 2D liquid ionization array with high resolution has been designed for the verification of treatments in Stereotactic Radiosurgery (SRS) and Radiotherapy (SRT).
Methods:
Firstly, a small prototype has been built. It is a matrix of 128 pixels arranged in a 16x8 rectangle filled with non-ultrapure isooctane. Each detector has a 2x2 mm² section and a thickness of 0.5 mm.
This array has been characterized by studying the dependencies with dose, dose rate, field size, depth and the angle of incidence.
We have used this 2Darray in the quality assurance of a linac by measuring output factors, transmission, tongue and groove effect and garden fence test. We have used it also for the verification of an IMRT treatment.
Based on this characterization a final prototype has been made consisting in a square matrix of 256 detectors which covers 5x5 cm². Each detector has a 3x3 mm² and a thickness of 0.5 mm.
This detector has been used to commission a machine model in Pinnacle treatment Planning System which corresponds to a micromultileaf from BrainLab attached to a Mevatron Primus from Siemens.
Results:
Dependencies of different parameters are low enough except for the angle of incidence. To overcome this problem we have calculated a correction factor depending on the angles.
The output factors measurements agree within 1% with unshielded diode measurements. The measurement of the IMRT treatment has been compared with a CC01 chamber and EDR2 films showing and excellent agreement (100% passing rates for 1.8% and 1.8 mm tolerances).
The final machine model accepted in Pinnacle agrees with the 2D detector considering gamma coefficient tolerances of 2% and 2 mm.
Conclusions:
A new 2D array detector with high spatial resolution has been characterized and used in different tests showing excellent properties for the quality assurance in radiotherapy.

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