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On the Quality of Photon Beam Data Acquisition for Radiation Therapy Beam Modeling Using a New Commercially Available Water Tank System

S Stathakis

S Stathakis*, A Alexandrian , C Kabat , H Parenica , K Rasmussen , N Kirby , D Saenz , N Papanikolaou , University of Texas HSC SA, San Antonio, TX


SU-I-GPD-T-542 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate the effect of beam data acquisition parameters during commissioning of small fields used for stereotactic radiosurgery (SRS) and for very large fields.

Methods: The PTW BeamScan water tank system was used for the measurements of small fields (less than 3x3cm2 and SRS cones of 6mm, 7.5mm and 10mm and very large (>20x20cm2). Beam data was acquired both in continuous mode and in stepwise vs. time modes. The detector speed during continuous mode varied from 5mm/sec to 20mm/sec and the integration time set to 0.3sec for the discrete acquisition mode. The penumbra, flatness, symmetry and central axis (CAX) deviations were used for comparison of the profiles, while the dmax location, dose at 10cm and the dose at 20cm were used for the percent depth dose (PDD) comparison. Measurements were performed using a PTW pinpoint and a PTW diode.

Results: The differences for the PDD curves measured with the pinpoint chamber were within 0.5% except for the 0.6mm where a 0.8% was observed down to 7cm deoth. D10 and D20 were all within 0.5%. Profile differences measured with the diode did not show any significant differences. The smallest penumbra was observed during continuous acquisition at 5mm/sec speed. The penumbras were all measured within 0.5mm for small fields and within 2.0mm for large fields. The flatness and symmetry were within 0.7% and the CAX deviation was within 0.2mm. While all measurements were within acceptable criteria, the continuous acquisition measurements were obtained at least two times faster than discrete acquisition measurements.

Conclusion: The PTW BeamScan water tank system used in the continuous beam acquisition mode was able to reproduce the beam data acquired using discrete measurements. The data did not suffer in quality while the time savings can be substantial.

Funding Support, Disclosures, and Conflict of Interest: PTW NY research grant.

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