Optimizing Film Delivery for Patient-Specific QA for Trigeminal Neuralgia.
Abstract
Purpose
To compare two patient-specific quality assurance measurements for trigeminal neuralgia (TN) treatments to ensure that the QA delivery matches the mechanical treatment limitations.
Methods
Verification plans were generated from five patient plans used to treat trigeminal neuralgia with dose prescribed to a 5 mm sphere, dMax from 70-85Gy using ten partial arcs. Two verification plans, scaled-dose and five-arc, were created for all patients. Scaled-dose verification plans were created by reducing the clinical plan dmax to 20Gy then mapping the resulting plan onto a cylindrical polystyrene phantom. The scaled-dose plans show reduced variation in gantry speed compared to the clinical plans. For five-arc verification plans, the clinical plan was first mapped onto the phantom and every second treatment arc was deleted, reducing the dmax to fit onto EBT-XD Gafchromic film. Plans were delivered using a Varian TrueBeam Edge with a single EBT-XD film placed at isocenter. Film dose maps were compared to exported dose planes. The radial full-width half-max (FWHM) values were measured in X, Y, and radial directions. Radial FWHMs were calculated by averaging all pixel values at each radial distance from dmax and computing the FWHM on the resulting array.
Results
FWHM means were 5.23±0.21mm, 5.07±0.17mm, 4.89±0.11mm for scaled dose X, Y, and radial FWHMs respectively and 5.3±0.25mm, 5.15±0.21mm, 4.99±0.12mm for five-arc X, Y, and radial FWHMs respectively. FWHM mean differences between exported and delivered plans were -0.69±0.25mm, -0.75±0.20mm, and -0.47±0.16mm for scaled dose X, Y, and radial FWHMs respectively and -0.62±0.29mm, -0.67±0.25mm, and -0.38±0.20mm for five-arc X, Y, and radial FWHMs respectively.
Conclusion
Both QA plans agreed within uncertainties and with the 5mm sphere goal. The five-arc QA plans keep the mechanical characteristics of the treatment delivery and should be favoured for patient-specific TN QA.