Room: Exhibit Hall
Purpose: To determine the performance of SNC Machine for a range of QC tests.
Methods: The QC tests selected for sensitivity testing were: picket fence, RapidArc â€“ dose rate and gantry speed (DR+GS), RapidArc - leaf speed (LS), field size, flatness, symmetry and Winston-Lutz (WL). A picket fence test was delivered with deliberate MLC positioning errors of 0.5mm.The RapidArc DR+GS and LS were tested by reducing the fluence on the first of several ideally equal fluence sections, DR+GS first section 9.01% lower, LS first section 2.01% lower. Field size was tested using images acquired with 1mm alternate X jaw adjustments from 26.7cm to 27.3cm.Flatness was measured; deviations were created by introducing 1cm slices of solid water onto the linac head, at G180Â°, up to 4cm.A STARCHECKáµ?áµƒË£â?± was used to measure symmetry, then steer 1% symmetry changes, up to 3%.A WL acquisition was performed; moves were made in X, Y and Z directions of approximately 1mm.
Results: The picket fence reported a maximum leaf error of 0.58mm (0.5mm expected), with 1mm action level.RapidArc DR+GS test reported the first section 10.6% lower (9.01% expected) and RapidArc LS first section 2.1% lower (expected 2.01%), the tolerance and action levels are 2% and 3% respectively.The measured flatness (Variance definition) for each measurement was 2.46% (0cm), 2.75% (1cm), 3.04% (2cm), 3.29% (3cm), 3.59% (4cm). The mean symmetry change was 0.88% (1% expected) (normalised point difference definition). Recommended action level for changes from baseline is 1% for flatness and symmetry. The mean difference from expected field size is 0.03mm, Ïƒ = 0.02mm, with a recommended 1mm action level. WL results after approximately 1mm moves, Î”X 1.10mm, Î”Y 0.91mm and Î”Z 0.44mm, action level of 1mm.
Conclusion: SNC Machine is able to detect changes in machine performance below TG-142 action levels.
Quality Assurance, Linear Accelerator
TH- External beam- photons: Quality Assurance - Linear accelerator