(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: A comparison of the gamma index analysis in ArcCHECK and Portal dosimetry (PD) systems for volumetric modulated arc therapy (VMAT) on Halcyon.
Methods: 14 clinical plans from a variety of sites were considered. Measurements using two detectors (ArcCHECK and EPID) were used to validate the dosimetric accuracy of the VMAT delivery for per-field and composite measurements. Gamma index analysis (2%/1-,1%/2-,2%/2-, and3%/3-mm dose difference and DTA criteria, ≥10% standard lower threshold dose limits) was conducted to compare calculated and delivered dose distributions. For PD comparison, local and global gamma passing rate were used. For ArcCHECK, the gamma criteria were analyzed and presented in relative and absolute ways.
Results: With 3%/3mm gamma criteria, the average pass rate of the Halcyon VMAT plans for ArcCHECK by composite fields was 99.72±0.63% (relative) and 96.82±2.35% (absolute), the field-by-field pass rate is 98.10±3.83% (relative) and 95.14±6.34% (Absolute). The average pass rate (3%/3mm) of the Halcyon VMAT plans for PD by composite fields was 99.88 ± 0.17% (Local) and 99.99 ± 0.03% (Improved), the field-by-field pass rate is 98.87 ± 2.37% (Local) and 99.57 ± 1.46 %(Improved).
Conclusion: ArcCHECK and PD can be used for Halcyon pretreatment VMAT plan QA. The novel Halcyon system showed good dosimetric agreement between the measured and calculated dose for treatment delivery of VMAT.
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