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Accuracy of Patient Dose Calculation for Lung VMAT Plans: Comparison of Multiple TPS

X Wang

X Wang1*, (1) Northeastern Ontario Regional Cancer, Sudbury, ON

SU-E-T-634 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To evaluate the discrepancy in patient dose calculation for lung VMAT SBRT plans calculated either using the same type treatment planning systems (TPS) commissioned in different hospitals or the different type TPS commissioned in the same hospital.

10 lung SBRT cases have been calculated using four different TPS. TPS A, B, and C are Pinnacle3 (version 9) and each one is commissioned in a different hospital for 6 MV photon beams (Varian Trilogy, 120 MLC). Therefore, beam data and parameters used in these TPS are not exactly the same. The TPS D is Eclipse (version 10) and uses the same machine data as the TPS A. The variations of PDD (10)/PDD (20) ratios for three 6 MV beams are within 0.5%. MU are rescaled for TPS A, B, and C to get a normalized dose in a reference condition. TPS A and D use the same MU. The Dmean for IGTV and PTV, D50, D99, D2 for PTV, D2cm, cord Dams, Dmean, V20 and V10 for lung are used for comparison. Cases with large discrepancy are also recalled in typically used lung QA phantoms (ROTG and Quasar).

The doses calculated using different Pinnacle TPS have no clinical significantly discrepancy. The largest discrepancy in PTV mean dose is 3%. In most cases the dose discrepancy between the Eclipse and Pinnacle is also small but the largest discrepancy is up to 7% in PTV mean dose. Dose calculation in lung phantoms cannot predict the corresponding discrepancy in patients.

The same type PTS even commissioned in different hospitals will have minimum calculated discrepancy. Using different type TPS have largest discrepancy especially for a tumour surrounded unusual lower density lung volume. Centralized modeling with comprehensive QA will improve dose calculation accuracy to achieve a standardized treatment.

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