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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

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.

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).

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.

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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