Acuros XB Dose Calculation Algorithm Research Articles

SU-E-T-67: Clinical Implementation and Evaluation of the Acuros Dose Calculation Algorithm

Purpose: The main aim of the current study is to present a detailed description of the implementation of the Acuros XB Dose Calculation Algorithm, and subsequently evaluate its clinical impacts by comparing it with AAA algorithm. Methods: The source models for both Acuros XB and AAA were configured by importing the same measured beam data into Eclipse treatment planning system. Both algorithms were evaluated by comparing calculated dose with measured dose on a homogeneous water phantom for field sizes ranging from 6cm × 6cm to 40cm × 40cm. Central axis and off-axis points with different depths were chosen for the comparison. Similarly, wedge fields with wedge angles from 15 to 60 degree were used. In addition, variable field sizes for a heterogeneous phantom were used to evaluate the Acuros algorithm. Finally, both Acuros and AAA were tested on VMAT patient plans for various sites. Does distributions and calculation time were compared. Results: On average, computation time is reduced by at least 50% by Acuros XB compared with AAA on single fields and VMAT plans. When used for open 6MV photon beams on homogeneous water phantom, both Acuros XB and AAA calculated doses were within 1% of measurement. For 23 MV photon beams, the calculated doses were within 1.5% of measured doses for Acuros XB and 2% for AAA. When heterogeneous phantom was used, Acuros XB also improved on accuracy. Conclusion: Compared with AAA, Acuros XB can improve accuracy while significantly reduce computation time for VMAT plans.

PO-0824: Dosimetric impact of Acuros XB dose calculation algorithm on PTV in head and neck treatments using VMAT

PO-0824: Dosimetric impact of Acuros XB dose calculation algorithm on PTV in head and neck treatments using VMAT

Clinical Impact and Utility of Acuros XB Dose Calculation Algorithm in Lung Stereotactic Body Radiation Therapy

Clinical Impact and Utility of Acuros XB Dose Calculation Algorithm in Lung Stereotactic Body Radiation Therapy

SU‐E‐T‐423: Effect of X‐Ray Source Spot Size Modeling in AcurosXB Dose Calculation Algorithm On VMAT Based SBRT Treatments

Purpose: Aim of this study is to evaluate AcurosXB(AXB) dose calculation algorithm dosimetrically with different X‐ray source spot size modeling and its clinical effect on Volumetric Modulated Arc Therapy(VMAT) based Stereotactic Body Radiotherapy(SBRT). Methods: 10 SBRT cases were purposely selected to analyze the effect of source spot size for smaller field size. All the cases were planned in Varian Eclipse(V10.0) treatment planning system(TPS) which uses AXB algorithm for VMAT dose computation. For this study source spot sizes varied from 0.5mm, 1.0mm, 1.5mm and 2.0mm in X as well as Y‐direction in the beam data configuration. SBRT plans were optimized using Progressive Resolution Optimizer III(PRO‐III) and dose was calculated by AXB with different source spot sizes. Plan quality index such as conformity index(CI) and gradient measure for PTV and for normal tissues volume of 90% and 25% prescribed dose were used for analysis. VMAT plans were delivered with Varian Clinac‐iX and 2D‐planner dose was measured using iba iMatrixx 2D array in Multicube phantom. Gamma (3mm/3%) analyses were performed between measured and predicted doses for different spot sizes. Results: Conformity index value for PTV were found to be 1.16±0.21, 1.14±0.20, 1.13±0.2 & 1.08±0.17 and gradient measure were 1.45±0.26, 1.46±0.26, 1.47±0.25 & 1.52±0.27 for spot size of 0.5mm, 1.0mm, 1.5mm & 2.0mm respectively. Volume of normal tissue receiving 90% of prescribed dose for 2mm spot size was 2.7% more in compare to 0.5mm spot size. Gamma analysis(3mm/3%) were found to be 98.77±1.03%, 98.96±0.91%, 99.18±0.76% & 99.43±0.60% for spot size 0.5mm, 1.0mm, 1.5mm & 2.0mm respectively. Conclusion: The Result showed that spot size configuration of 1.5–2.0mm were matching very closely with our measurements. Based on the variation in the PTV coverage and dose to normal tissues it is highly recommended to fine tune spot size parameters for VMAT based SBRT.

Dosimetric evaluation of Acuros XB dose calculation algorithm with measurements in predicting doses beyond different air gap thickness for smaller and larger field sizes

In this study, dose prediction accuracy of Acuros XB (AXB) dose calculation algorithm beyond air gap thickness (range 2, 4, and 6 cm) in simple inhomogeneous phantoms was investigated. The evaluation of AXB was performed by comparing the doses calculated by AXB with the doses calculated by Anisotropic Analytical Algorithm (AAA) and the measured data for different field sizes (3 × 3, 5 × 5, and 10 × 10 cm2) of a 6 MV photon beam. The dose computation was performed within Eclipse treatment planning system, and measurements were acquired with a cylindrical ionization chamber. Central axis depth dose comparisons were done in solid–water material region up to 5 cm distance from air/solid—water interface. The results of AXB had better agreement with measurements at all measured points than that of AAA. The discrepancies between AXB and measured data were seen from − 3.81% to + 0.9%, whereas the AAA differences with measurement from − 3.1% to − 10.9%. The combination of the smallest test field size and the largest air gap produced the highest range (1-5 cm distance from air/solid–water interface) in dose difference (AAA: −4.0% to − 10.6% and AXB: −3.8% to + 0.6%). The AAA computational time was about 8 times faster than that of AXB. In conclusion, AXB is more appropriate to use for dose predictions, especially when low-density heterogeneities are involved.

Dosimetric impact of Acuros XB dose calculation algorithm in prostate cancer treatment using RapidArc

The purpose of this study is to assess the dosimetric impact of Acuros XB dose calculation algorithm (AXB), in comparisons with Anisotropic Analytical Algorithm (AAA) calculations in prostate cancer treatment using RapidArc. A computed tomography (CT) dataset of low-risk prostate cancer patients treated at Arizona Center for Cancer Care was selected and contoured for prostate, seminal vesicles, and organs at risk (OARs)(rectum, bladder, and femur heads). Plans were created for 6 MV photon beam using RapidArc technique in Eclipse treatment planning system. Dose calculations were performed with AAA and AXB for same number of monitor units and identical beam setup. Mean and maximum doses to planning target volume (PTV) and OARs were analyzed. Additionally, minimum dose to PTV and V100 was analyzed. Finally, point-dose difference between planar dose distributions of AAA and AXB plans was investigated. The highest dose difference was up to 0.43% (range: 0.05-0.43%, P> 0.05) for PTV and 1.98% (range: 0.22-1.98%, P> 0.05) for OARs with AAA predicting higher dose than AXB. The V100 values of AAA plans (95 %) and AXB plans (range: 93.1-97.9 %) had an average difference of 0.89 ± 1.47% with no statistical significance (P = 0.25411). The point-dose difference analysis showed that AAA predicted higher dose than AXB at significantly higher percentage (in average 94.15) of total evaluated points. The dosimetric results of this study suggest that the AXB can perform the dose computation comparable to AAA in RapidArc prostate cancer treatment plans that are generated by a partial single-arc technique.

SU-E-T-516: Dosimetric Validation of AcurosXB Algorithm in Comparison with AAA & CCC Algorithms for VMAT Technique.

To dosimetrically validate AcurosXB algorithm for Volumetric Modulated Arc Therapy (VMAT) in comparison with standard clinical Anisotropic Analytic Algorithm(AAA) and Collapsed Cone Convolution(CCC) dose calculation algorithms. AcurosXB dose calculation algorithm is available with Varian Eclipse treatment planning system (V10). It uses grid-based Boltzmann equation solver to predict dose precisely in lesser time. This study was made to realize algorithms ability to predict dose accurately as its delivery for which five clinical cases each of Brain, Head&Neck, Thoracic, Pelvic and SBRT were taken. Verification plans were created on multicube phantom with iMatrixx-2D detector array and then dose prediction was done with AcurosXB, AAA & CCC (COMPASS System) algorithm and the same were delivered onto CLINAC-iX treatment machine. Delivered dose was captured in iMatrixx plane for all 25 plans. Measured dose was taken as reference to quantify the agreement between AcurosXB calculation algorithm against previously validated AAA and CCC algorithm. Gamma evaluation was performed with clinical criteria distance-to-agreement 3&2mm and dose difference 3&2% in omnipro-I'MRT software. Plans were evaluated in terms of correlation coefficient, quantitative area gamma and average gamma. Study shows good agreement between mean correlation 0.9979±0.0012, 0.9984±0.0009 & 0.9979±0.0011 for AAA, CCC & Acuros respectively. Mean area gamma for criteria 3mm/3% was found to be 98.80±1.04, 98.14±2.31, 98.08±2.01 and 2mm/2% was found to be 93.94±3.83, 87.17±10.54 & 92.36±5.46 for AAA, CCC & Acuros respectively. Mean average gamma for 3mm/3% was 0.26±0.07, 0.42±0.08, 0.28±0.09 and 2mm/2% was found to be 0.39±0.10, 0.64±0.11, 0.42±0.13 for AAA, CCC & Acuros respectively. This study demonstrated that the AcurosXB algorithm had a good agreement with the AAA & CCC in terms of dose prediction. In conclusion AcurosXB algorithm provides a valid, accurate and speedy alternative to AAA and CCC algorithms in a busy clinical environment.

SU-E-T-525: Dosimetric Validation of the Algorithm Based on Linear Boltzmann Transport Equations for Photon 4MV Dose Calculation.

To evaluate a dosimetric accuracy of AcurosXB dose calculation algorithm for 4 MV photon beam. Four MV beam (Clinac-6EX) and AAA and AcurosXB algorithms (pre-release version 11.0.03.) were used in this study. The differences of the calculation with AAA (EAAA) and AcurosXB (EAXB) to the measurement were evaluated in the depth doses to 25 cm depth and dose profiles within the water and slab phantoms (water, lung and bone equivalent). In addition, the clinical cases, including three whole breast plans and three head and neck IMRT plans, were evaluated. First the AAA plans were calculated, then AcurosXB plans were recalculated with dose-to-medium with identical beam setup and monitor units as in the AAA plan. In the water phantom study, the EAAA and EAXB were up to 2.2% and 1.5% in the depth doses for the open field (field size = 4 - 40cm square), respectively. Under the heterogeneity conditions, the EAAA and EAXB were less than 4.4% and 2.2% in lung region, and less than 12.5% and 6.3% in bone region, respectively. In the re-buildup region after passing through the lung phantom, the AAA overestimated the doses about 10%; however AcurosXB had good agreement with measurement within 3%. Dose profiles with AcurosXB were better agreement with measurement than AAA. In the clinical cases, the dose of the skin surface region with AcurosXB were higher than AAA by at least 10%, and the dose differences over 5% appeared in heterogeneous region. However, DVH shapes of each organ were similar between AAA and AcurosXB within 2%. In phantom study, AcurosXB had better agreement to measurement than AAA, especially in heterogeneous region and re-buildup region. In the clinical cases, there were large differences between AcurosXB and AAA in the surface region. Evaluation Agreement of non-clinical versions of Acuros XB with　Varian Medical Systems.

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

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 cm2 to 5 × 5 cm2 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.

SU‐E‐T‐702: Accuracy of a Commercially Available Dose Calculation Algorithm for Small Field Dosimetry

Purpose: To validate the AcurosXB dose calculation algorithm for small field dosimetry for high energy photon beams. Methods: Calculations in water phantom of 0.2×0.2×0,2cm3 voxel size with slabs of inhomogeneity materials (air rho=0.0012g/cm3, lung rho =0.2 g/cm3 and bone rho =1.85 g/cm3) were used in this study. Fields sizes ranging from 1×1cm2 to 10×10cm2 and energies of 6, 10 and 18MV were calculated using the Acuros XB dose calculation algorithm available in the Eclipse treatment planning system (TPS). The calculations were compared to the Analytical Anisotropic Algorithm (AAA) also available in Eclipse as well to Collapsed Cone Convolution Superposition (CCCS) algorithm available in the Pinnacle3 TPS. Comparison between the dose calculations and Monte Carlo calculations using EGSnrc\BEAMnrc and EGSnrc\DOSXYZnrc package was also performed. Results: The AcurosXB calculation algorithm was in general in good agreement with Monte Carlo calculations. Discrepancies were observed at the interfaces of the inhomogeneities. Good agreement between CCCS and AcurosXB was also observed for the majority of the cases with discrepancies observed only at the interfaces of the media. The AAA did not successfully calculate the dose for the test geometries when small fields were used. Discrepancies in the order of 50–70% were observed. The AAA overestimated the dose in the low density material and failed to predict the second buildup region accurately for the very small field sizes. Conclusion: In general, the overall degree of accuracy for AcurosXB in the conditions of electronic disequilibrium was in good agreement with Monte Carlo calculations (within 2%) and comparable with the CCCS algorithm. The AAA on the other hand failed to accurately predict the dose for the small fields studied in the presence of inhomogeneities