Accuracy of the Small Field Dosimetry Using the Acuros XB Dose Calculation Algorithm within and beyond Heterogeneous Media for 6 MV Photon Beams

Abstract

Purpose: The dosimetric accuracy of the recently released Acuros XB advanced dose calculation algorithm (Varian Medical Systems, Palo Alto, CA) is investigated for single radiation fields incident on homogeneous and heterogeneous geometries, as well as for two arc (VMAT) cases and compared against the analytical anisotropic algorithm (AAA), the collapsed cone convolution superposition algorithm (CCCS) and Monte Carlo (MC) calculations for the same geometries. Methods and Materials: Small open fields ranging from 1 × 1 cm 2 to 5 × 5 cm 2 were used for part of this study. The fields were incident on phantoms containing lung, air, and bone inhomogeneities. The dosimetric accuracy of Acuros XB, AAA and CCCS in the presence of the inhomogeneities was compared against BEAMnrc/DOSXYZnrc calculations that were considered as the benchmark. Furthermore, two clinical cases of arc deliveries were used to test the accuracy of the dose calculation algorithms against MC. Results: Open field tests in a homogeneous phantom showed good agreement between all dose calculation algorithms and MC. The dose agreement was +/−1.5% for all field sizes and energies. Dose calculation in heterogenous phantoms showed that the agreement between Acuros XB and CCCS was within 2% in the case of lung and bone. AAA calculations showed deviation of approximately 5%. In the case of the air heterogeneity, the differences were larger for all calculations algorithms. The calculation in the patient CT for a lung and bone (paraspinal targets) showed that all dose calculation algorithms predicted the dose in the middle of the target accurately; however, small differences (2%-5%) were observed at the low dose region. Overall, when compared to MC, the Acuros XB and CCCS had better agreement than AAA. Conclusions: The Acuros XB calculation algorithm in the newest version of the Eclipse treatment planning system is an improvement over the existing AAA algorithm. The results are comparable to CCCS and MC calculations especially for both stylized and clinical cases. Dose discrepancies were observed for extreme cases in the presence of air inhomogeneities.

Clinical dosimetric impact of Acuros XB and analytical anisotropic algorithm (AAA) on real lung cancer treatment plans : review

“…[16][17][18][19][20][21][22][23][29][30][31][32][33][34] For instance, in MC study involving low-density lung, Bush et al 17 showed the difference between the MC and AAA was higher (up to 17.5%) when compared to the one between the MC and AXB (up to 4.5%). In a phantom study involving low-density medium (lung insert and air gap), Rana et al 29 showed that the dose prediction error of the AAA could be up to 12.5% when compared to the measurements, whereas the AXB had better agreement with the measurements with a difference up to 2.8%.…”

“…16 Detail descriptions on the AXB can be found elsewhere. [16][17] Current literature on the AXB shows that several investigators have validated the AXB by performing measurements and Monte Carlo (MC) simulations [16][17][18][19][20][21][22][23] and reported better dose prediction accuracy using the AXB than using the AAA in heterogeneous media. If the AXB is more accurate than the AAA, it is imperative to evaluate the clinical dosimetric impact of the AXB on real cancer treatment plans.…”

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

“…Notable was that it was one of the rare studies, where other TPS algorithm, the XVMC in this case, achieved more accurate results than the AXB algorithm, when comparing to the reference method. Stathakis et al 34 assessed the accuracy of the AXB10 with small fields (1 × 1 -5 × 5 cm 2 ) in water phantoms containing lung, bone or air inserts for 6 MV beams by comparing to full MC simulations and the AAA and the CCC algorithm implemented in Pinnacle TPS. The agreement between the AXB10 and full MC simulations was within 2% for lung and bone, but for the phantom with air, the deviations were larger -ranging from 3 to 15%.…”

“…The deviations in DVH parameter values between the AXB11 and the XVMC algorithm were less than 2.5%. In the study by Stathakis et al 34 jaw-collimated arc plans for lung and paraspinal lesion radiotherapy were used to benchmark the AXB10, the AAA and the CCC algorithm found in Oncentra MasterPlan against full MC simulations. With all the algorithms the deviations to full MC simulations ranged from 2% to 5%, the AXB10 being one of the algorithms with smallest discrepancies.…”

A Monte Carlo approach to lung dose calculation in small fields used in intensity modulated radiation therapy and stereotactic body radiation therapy

“…[18] The BEAMnrc/DOSXYZnrc code calculations were used in their study and two other analytical algorithms were assessed against MC results. The dose reduction inside lung was obtained for 1 cm × 1 cm, 2 cm × 2 cm and 3 cm × 3 cm field sizes.…”