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Verification and Dosimetric Impact of Acuros XB Algorithm for Stereotactic Body Radiation Therapy (SBRT) and RapidArc Planning for Non-Small-Cell Lung Cancer (NSCLC) Patients


Suresh Rana

S Rana1*, K Rogers2, (1) ProCure Proton Therapy Center, OKLAHOMA CITY, OK, (2) Arizona Center for Cancer Care, Peoria, AZ

PO-BPC-Exhibit Hall-4 Saturday  Room: Exhibit Hall

Purpose:
The experimental verification of Acuros XB (AXB) algorithm was conducted in a heterogeneous slab phantom, and compared to Anisotropic Analytical Algorithm (AAA). The dosimetric impact of AXB for stereotactic body radiation therapy (SBRT) and RapidArc planning for 16 non-small-cell lung cancer (NSCLC) patients was assessed.

Methods:
The calculated central axis percentage depth doses (PDD) in a phantom for an open field size (3x3 cm2) were compared against PDD measured by an ionization chamber. For 16 NSCLC patients, dose-volume parameters from treatment plans calculated by AXB and AAA were compared using identical jaw settings, leaf positions, and monitor units (MUs).

Results:
The results from the phantom study showed that AXB was more accurate than AAA; however, dose underestimation by AXB (up to -3.9%) and AAA (up to -13.5%) was observed. For a planning target volume (PTV) in NSCLC patients, in comparison to AAA, the AXB predicted lower mean and minimum doses by average 0.3% and 4.3% respectively, but a higher maximum dose by average 2.3%. The averaged maximum doses to heart and spinal cord predicted by AXB were lower by 1.3% and 2.6% respectively; whereas doses to lungs predicted by AXB were higher by up to 0.5% compared to AAA. The percentage of ipsilateral lung volume receiving at least 20 and 5 Gy were higher in AXB plans than in AAA plans by average 1.1% and 2.8% respectively. The AXB plans produced higher target heterogeneity by average 4.5% and lower plan conformity by average 5.8% compared to AAA plans. Using AXB, the PTV coverage was reduced by average 8.2% than using AAA.

Conclusion:
AXB is more accurate to use for dose calculations in SBRT lung plans created with a RapidArc technique; however, one should also note reduced PTV coverage due to dose recalculation from AAA to AXB.

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