Author: Vibha Chaswal, Stephen D. Davis, Alonso N. Gutierrez, Noah S. Kalman, Yongsook C. Lee, William Romaguera, Ranjini P. Tolakanahalli, D. Jay J. Wieczorek 👨🔬
Affiliation: Miami Cancer Institute, Baptist Health South Florida 🌍
Purpose: To report machine performance of our superficial radiation therapy unit (SRT-100 Vision, Sensus Healthcare, Boca Raton, FL) for the first three years after commissioning of the unit.
Methods: Periodic quality assurance (QA) tests for the SRT-100 Vision performed for the first three years were retrospectively reviewed and analyzed. The QA tests included (daily) output constancy with x-ray tube head straight, backup timer, timer accuracy, (annual) output constancy with varying head tilt (head angle: 0° (head straight up), 90°, 135°, 180°, and 225°), output reproducibility for ten consecutive measurements (=standard deviation/mean×100%), output linearity (R2 value of linear regression line), timer and end errors, half value layer (HVL), applicator factors for six applicators (1.5, 2, 2.5, 3, 4 and 5 cm in diameter), absolute output calibration (TG-61 protocol), percent depth dose (PDD) and congruence between radiation field and applicator size at focal spot distance (15 cm) for commissioned energies of 50, 70 and 100 kVp.
Results: The following three-year results were observed for the three energies: Daily outputs with head straight were within ±3.0% from baselines. Backup timer consistently recorded the same value as the timer set. Timer accuracy was ≤±1 sec of the timer set. Outputs with varying head tilt were ≤±1.0% of output with head straight. Output reproducibility was <0.1%. R2 values for output linearity were 1.0000. Timer and end errors were within ±0.0005 min. HVLs were <±1.0% from baselines. Applicator factors and absolute outputs were <±0.2% and <±1.2% from baselines, respectively. PDD for 5 cm applicator remained within ±0.9% from baselines for a depth up to 5 mm. Radiation field sizes for all six applicators were within ±0.4 mm.
Conclusion: Periodic QA test results over the first three years of operation were well within the recommended tolerances, thereby demonstrating high performance and stability of our SRT-100 Vision unit.