PTW QUICKCHECKwebline: Daily quality assurance phantom comparison and overall performance.

PURPOSE: The Daily QATM3 phantom from Sun Nuclear Corporation has been a popular daily quality assurance (QA) tool for many institutions. PTW has recently introduced the QUICKCHECKwebline phantom as an alternative. The goal of this study was to compare these two commercially available devices for daily quality assurance measurements of a linear accelerator and assess the overall performance of the new phantom. METHODS: Two daily QA phantoms (PTW QUICKCHECKwebline and Sun Nuclear Corporation Daily QATM3) were measured over a 4-month period using a 20x20cm² field size and delivering 150 MU. Photon energies of 6 and 18 MV were measured on a daily basis, and electron energies of 6, 9, 12, 15, and 18 MeV were measured weekly on a 23EX Varian Linear Accelerator. Consistency of the dose output, beam flatness, in-plane and cross-plane symmetry, and beam quality were evaluated. RESULTS: The QUICKCHECKwebline and Daily QATM3 performed with maximum percent differences from baseline of -0.97% and 1.12% for output, 1.36% and 0.82% for flatness, 0.86% and -1.36% for in-plane symmetry, -1.41% and 1.00% for cross-plane symmetry, and -0.91% and 1.29% for beam quality respectively over all energies. CONCLUSION: Consistent and accurate measurements over a 4-month period, a user-friendly interface, and wireless features prove the QUICKCHECKwebline would be a suitable phantom for daily quality assurance use.

Clinical Commissioning of a Pencil Beam Scanning Treatment Planning System for Proton Therapy.

PURPOSE: In this report, we present the commissioning and validation results for a commercial proton pencil beam scanning RayStation treatment planning system. MATERIALS AND METHODS: The commissioning data requirements are (1) integrated depth dose curves, (2) spot profiles, (3) absolute dose/monitor unit calibration, and (4) virtual source position. An 8-cm parallel plate chamber was used to measure the integrated depth dose curves by scanning a beam composed of a single spot in a water phantom. The spot profiles were measured at 5 different planes using a 2-dimensional scintillation detector. The absolute dose/monitor unit calibration was based on dose measurements in single-layer fields of size 10 × 10 cm2. The virtual-source position was calculated from the change in spot spacing with the distance from the isocenter. The beam model validation consisted of a comparison against commissioning data as well as a new set of verification measurements. For end-to-end testing, a series of phantom plans were created. These plans were measured at 1 to 3 depths using a 2-dimensional ion chamber array and evaluated for gamma index using the 3% and 3 mm criteria. RESULTS: The maximum deviation for spot sigma measured versus calculated was -0.2 mm. The point-dose measurements for single-layer beams were within ± 3%, except for the largest field size (29 × 29 cm2) and the highest energy (226 MeV). The point doses in the spread-out Bragg peak plans showed a trend in which differences > 3% were seen for ranges > 30 cm, field sizes > 15 × 15 cm2, and depths > 25 cm. For end-to-end testing, 34 planes corresponding to 13 beams were analyzed for gamma index with a minimum pass rate of 92.8%. CONCLUSION: The acceptable verification results and successful end-to-end testing ensured that all components of the treatment planning system were functional and the system was ready for clinical use.