Clinical Implementation of Calculation-Based Patient Specific QA for Lattice Radiotherapy Treatments
M MacFarlane1*, K Jiang1, M Guerrero1, K Spaeth1, K Marter1, B Zhang1, B Yi1, J Snyder2, J Molitoris1, S Chen1, (1) University of Maryland School of Medicine, Baltimore, MD, (2) University Of Alabama At Birmingham School of Medicine, Birmingham, AL
Presentations
PO-BPC-Virtual-30 (Saturday, 4/17/2021) [Eastern Time (GMT-4)]
Purpose: Lattice radiotherapy (LRT) is a novel form of spatially fractionated radiation therapy used to de-bulk large tumors. A LRT treatment plan consist of multiple VMAT arcs that have been inversely optimized to simultaneously deliver 3 Gy to the gross tumor volume (GTV) and 12-18 Gy to a 3D lattice of spheres contained in the GTV. These LRT treatments plans are often highly modulated and contain many small fields, which could result in dose calculation errors. As a result, laborious patient specific IMRT QA measurements are often performed to confirm the accuracy of the calculated dose. In this work, we evaluated whether more time efficient calculation-based IMRT QA techniques could be used instead for patient specific QA.
Methods: Seven patients who were previously treated with LRT to the pelvis, abdomen and lung were evaluated in this study. Calculation-based IMRT QA was performed with Mobius3D while measurement-based IMRT QA was performed using a MapCheck 2 device. To improve the spatial resolution of the MapCheck measurements, multiple offset measurements were acquired with the MapCheck device, followed by merging of the measurement files using custom software. Gamma analyses were performed in both IMRT QA systems using the 3%/3mm acceptance criteria used clinically, and then the results were compared between systems. Factors such as the treatment location, GTV volume, and the ratio of MU to prescription dose (modulation factor) were also recorded.
Results: The median (min, max) global gamma-passing rate was 99.9 (99.6, 100) % with Mobius3D and 99.5 (96.1, 99.8) % with MapCheck. Neither the treatment location, GTV volume, nor modulation factor appeared to correlate with the passing rates.
Conclusion: The overall gamma pass rates of LRT plans agreed well between MapCheck measurements and more time-efficient Mobius3D calculations.
Keywords
Quality Assurance, Radiation Therapy
Taxonomy
TH- External Beam- Photons: Quality Assurance - IMRT/VMAT
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