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  4. Effect of ArcCHECK Array Calibration On Patient Specific Quality Assurance in Flattening Filter Free (FFF) Photon Beams

Effect of ArcCHECK Array Calibration On Patient Specific Quality Assurance in Flattening Filter Free (FFF) Photon Beams

S Srivastava1,2*, D Pinnaduwage1,2 , S Jani1,2 , X Yan1,2 , P Metuge1,2 , S Patel2 , N Thawani2 , S Mutyala2 , I Das3 , S Sorensen1,2 , (1) Barrow Neurological Institute, Phoenix, AZ, (2) University of Arizona Cancer Center \ Dignity Health, St. Joseph's Hospital, Phoenix, AZ, (3) NYU Langone Medical Center, New York, NY

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To investigate the energy dependence of the ArcCHECK array calibration on flattening filter free (FFF) photon beams and the resulting impact on patient-specific QA measurements.

Methods: ArcCHECK array calibrations were performed using 6MV, 10MV and 10FFF beams. Two Eclipse plan sets were generated on the ArcCHECK phantom for each energy: (1) open field plans with field sizes ranging from 3x3cm² to 20x20cm², at four cardinal gantry angles, and (2) single arc plans. 10FFF plans were created with 400 and 2400 MU/min. Measured and planned data were analyzed using the 10FFF ArcCHECK dose calibration using each of the array calibrations for the different beam energies, for the phantom plans, and for ten clinical plans.

Results: The 1%/1mm gamma (ƴ) passing rate for phantom measurements increases on average by 20±21% for 6MV and 10MV array calibrations compared to the 10 FFF. The average increase in 2%/2mm, and 3%/3mm passing rates were 10±10% and 7±11% for 6MV, and 9±7% and 7±11% for 10MV, array calibrations. For the ten patient plans, the 1%/1mm ƴ passing rate increases on average by 7±5% for 6MV, and 5±7% for 10MV array calibration compared with 10 FFF. An average increase of 5±3% and 4±2% was seen for 2%/2mm criteria for 6MV, 10MV array calibrations, while the increase in 3%/3mm passing rate was 2±2% for both. Average ƴ passing rate with ±3% absolute dose and ±3mm DTA criteria was higher with the 6MV array calibration (94.8%) compared to the 10FFF (92.7%) for clinical plans. This agreement gets worse for a 1%/1mm gamma criteria: 62.2% for 6MV vs. 57.8% for 10 FFF.

Conclusion: Our study shows that 6MV and 10MV array calibrations provide more accurate dose comparisons for 10FFF beams compared to using the 10FFF calibration, and should be used when performing FFF beam patient-specific QA.

Keywords

Radiation Dosimetry, Rotational Therapy, Treatment Verification

Taxonomy

TH- Radiation dose measurement devices: Multi-dimensional diode/chamber arrays

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