ABSTRACT
PURPOSE: To evaluate the heterogeneity corrected dose calculations from the Acuros XB (AXB), a novel deterministic dose calculation algorithm based on grid-based Boltzmann transport equation solver (GBBS), for IMRT and VMAT plans. METHODS: The Radiological Physics Center's lung phantom was used to create clinically equivalent IMRT and VMAT plans (RapidArc) with the Eclipse planning system 10.0 that were delivered using a Varian 23 iX. Absolute doses and relative dose distributions were measured with thermoluminescent dosimeters (TLDs) and radiochromic film. The measured dose distributions were compared with calculated doses from both AXB (11.0.3) and AAA (10.0.24) dose calculation algorithms. The AXB calculated dose-to-water and dose-to-medium were both compared to measurements. Gamma analysis (±7%/4mm, ±5%/3mm, and ±3%/3mm) was used to quantify correspondence between AXB dose distributions and the film measurements. The computation time between AAA and AXB were also evaluated. RESULTS: For TLD point doses, both AAA and AXB heterogeneity corrected dose calculations are within 5% inside the PTV for both IMRT and VMAT plans. The agreements observed between the measured and calculated doses for both AXB dose reporting methods are better than those observed with the AAA algorithm. The gamma analysis showed that the differences between AAA, AXB and film measurement met the RPC ±7%/4 mm criteria. The percent of pixels passing rate for both the AXB dose to medium and AXB dose to water are higher than AAA. The computation time between AAA and AXB are comparable for IMRT plans but AXB is significantly faster (4 times) than AAA for VMAT plans. CONCLUSIONS: The AXB implemented in the Eclipse planning system calculates a more accurate heterogeneity corrected dose than the AAA algorithm as compared to measurement in lung and improve the calculation speed for VMAT radiotherapy. Work supported by grants CA10953, CA81647, 2R44CA105806-02, CA016672 (NCI, DHHS).
ABSTRACT
PURPOSE: Compare the accuracy of AAA heterogeneity corrected dose calculation algorithm for high energy x-ray beams (>10 MV) for flattened and FFF beams using RPC anthropomorphic thorax phantom. METHODS: Six static beam SBRT treatment plans were created using the Varian Eclipse treatment planning system (TPS) AAA v.8.9.08 heterogeneity correction algorithm. Two flattened beam plans (6 MV and 18 MV) and four other plans (6 MV, 6 MV FFF, 10 MV FFF and 15 MV) were delivered using a Clinac 21EX and TrueBeam STx, respectively. Prescription dose/coverage, 6 Gy to 95% PTV, and constraints were the same for all plans. The phantom contained radiochromic films in the 3 major planes and TLDs in the heart, spine, and tumor. Point doses and 2D dose distributions were exported from the Eclipse TPS and compared with the measured doses. The gamma index analysis evaluation criteria of ±5% dose to agreement and 3 mm distance to agreement was used. RESULTS: TLD to TPS tumor point dose ratios were 0.971±0.006(6MV) and 0.957±0.002(6MV), 0.995±0.005(15MV), 1.114±0.006(18MV), and 0.957±0.003(6MV FFF), 0.974±0.011(10MV FFF) for the six plans. Using ±5%/3mm gamma analysis criteria, the average passing rates for all three films were 96.3% and 95.5%, 97.4%, 66.1%, 93.7%, and 96.3% for the 6 MV, 6 MV, 15 MV, 18 MV, 6 MV FFF, and 10 MV FFF plans, respectively. Dose profiles were also evaluated. CONCLUSIONS: The current RPC credentialing criteria are: RPC/Inst. tumor dose ratio of 0.97±0.05 and 85% of the pixels in each film plane must pass a ±5%/5mm gamma index analysis. These data demonstrate that the AAA heterogeneity correction dose calculation algorithm is accurate for photon energies in 6-15 MV range for flattened and FFF beams. Heterogeneity corrected dose calculations for photon energies >15 MV were not accurate. Work supported by grants CA10953 and CA81647 (NCI, DHHS).
