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Commissioning of the ArcCHECK Phantom

R Betancourt

R Betancourt1*, C Chang1, C Goldberg2, C Mesina1, (1) Hospital of the University of Pennsylvania, Philadelphia, PA, (2) Bryn Mawr, PA

SU-E-T-79 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: A study was undertaken to investigate the response of the ArcCHECK phantom distributed by Sun Nuclear (SNC) to different treatment modalities including Static, IMRT, Arc and VMAT and to understand patient-specific QA results.

Methods: An ArcCHECK kV-CT data image was acquired and two digital image sets assigned a uniform CT number of 145 Hounsfield units (HU) and 275 HU were created. Variable field sizes for the treatment modalities and sample treatment plans were calculated in Eclipse V8.9. Measurements on Varian linear accelerators with the ArcCHECK phantom were compared with dose calculations. Treatment plan QA results using our 2D QA device were also compared with ArcCHECK measurements.

Results: The average dose measured by ArcCHECK for the standard 10x10 cm² field was 311.64 +/- 3 cGy. Calculated static, standard arc and VMAT fields measured with ArcCHECK showed passing rate ranges of (51-89)%, (58-96)% and (83-98)% with averages of 64%, 85% and 90%, respectively when using kV-CT phantom. It was noted that exit points for all modalities lowered passing rates. When using the 275 HU digital phantom, passing rate ranges (80-100) % increased for all cases with the highest average of 97% for VMAT cases. The treatment plan QA passing rates using ArcCHECK differed by -3%, +3% and -0.5% for VMAT, VMAT SBRT and IMRT cases, respectively as compared with our standard QA device.

Conclusions: ArcCHECK's response when compared with Eclipse-generated calculations seemed to depend on whether the kV-CT data set (average uniform 145 HU) or the 275 HU digital phantoms was utilized, yielding passing rates of 90% and 97%, respectively. It seemed that Eclipse overestimated scattering at the distal points where they failed. The ArcCHECK phantom with its 3D array of 1386 diodes would capture exit dose information not measured with 2D QA devices, lowering the passing rate for fields.

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