Experience with Dose Validation for a New Planning System
Presentations
PO-GePV-P-18 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Planning doses are comprehensively validated after commissioning of Eclipse radiotherapy-planning-system(RTP) for Elekta Synergy-S and Agility linear-accelerators. We report the comparison of photon calculations using analytical-anisotropic-algorithm (AAA) and electron calculations using Monte-Carlo algorithm with measurements and our existing Pinnacle RTP using collapsed-cone-convolution (CCC) algorithm.
Methods: VMAT/IMRT plans of three head and neck, left and right breast, four lung, three prostate, and two female pelvis cases were generated for end-to-end tests. Point dose and dose distributions were measured using SunNuclear ArcCheck and MapCheck. For selected open and wedged X-ray fields and electron fields with small cutouts, we performed PDD and profile scans in water-tank, MapCheck measurements, and off-axis-ratio (OAR) measurements using calibrated ion chambers and microdiamond detector. Some Eclipse models and parameters for Elekta MLC and motorized-wedge were tweaked to improve the agreement between measurements and plans.
Results: The largest output factor difference was 0.6% (2.4cm-square photon fields) between Eclipse and Pinnacle RTPs. VMAT QAs show an average gamma passing rate (3mm/3% criteria, 10% threshold) of 97.7%±0.4% and 97.9%±0.4%, and the average point dose differences at the ArcCheck phantom center are -0.5%±0.2% and 2%±0.5%, respectively. Agility IMRT QAs show an average gamma passing rate of 98.7%±0.8%. A lower average gamma passing rates of 96.3% and 94.7% were observed for 60°-wedge fields of Agility and Synergy S machines. The OAR measurements show good agreements with Eclipse calculation (within 4% in the worst case). The largest output difference for 6MeV electron beams is 1% for 6cm-square cone but increased to 5% for 2cm-square cutout between Eclipse Monte-Carlo calculation and measurements.
Conclusion: Dose validations are of critical importance for accurate dose calculation using specific algorithms and various beam collimations. We found rooms to improve dose calculations for the wedge model, BeamModulator™ MLC model, and low energy electron beams with small cutouts during our validation.
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