Introduction Modern radiation therapies such as intensity-modulated radiation therapy (IMRT) and volume modulated arc therapy (VMAT) demand from dose calculation algorithms higher accuracy and computation speed Although the MC method can be considered as the gold standard in accuracy given sufficient particle histories, calculation times may not be short enough for clinical use with these advanced techniques. Recently, AcurosXB (AXB), a novel deterministic method based on the grid-based Boltzmann transport equation solver (GBBS), was introduced for external radiotherapy dose calculation and has shown poentials to improve the dose predictions over currently widely used convolution methods in heterogeneous media The goal of this study was to verify the dosimetric performance of AXB in IMRT and VMAT plans of lung cancer, in which the lung tissue heterogeneity may plays important role in dose calculation. We compare the AXB dose prediction with measured data from both TLD and film. We also compared with the Anisotropic Analytical Algorithm ( AAA). Conclusions The AXB was determined to be accurate using the RPC thorax phantom measurements and in equal or better agreement to both TLD and films than AAA. AXB dose-to-water in medium and AXB dose-to-medium in medium showed similar agreements to TLD and film measurements. AXB shorts the computation time 4 times over AAA for RapidArc plan. AXB shows promise for future dose calculations.oth in both accuracy and computation speed for lung cancer. References 1.Wareing, T., J. Morel, and J. McGhee, Coupled electron-photon transport methods on 3-D unstructured grids. Trans Am Nucl Soc, : p Gifford, K.A., et al., Optimization of deterministic transport parameters for the calculation of the dose distribution around a high dose-rate 192Ir brachytherapy source. Med Phys, (6): p Vassiliev, N.O., et al., Validation of a new grid- based Boltzmann equation solver for dose calculation in radiotherapy with photon beams. Phys. Med. Biol , Han, T., et al., Dosimetric comparison of Acuros XB deterministic radiation transport method with Monte Carlo and model-based convolution methods in heterogeneous media. Med Phys, Methods & Materials RPC thorax phantom 4 TLD tublets 3 EBT2 films (axial,sagittal, coronal) Varian Eclipse TPS 11.0 AAA AXB Dose-to-water in medium (AXB_mw) Dose-to-medium in medium (AXB_mm) Clinically equivalent IMRT and VMAT (RapidArc) plans were generated on Eclipse 9 fields IMRT 2 arcs RapidArc Each plan delivered 3 times Dose grid sizes: 0.1x0.1x0.1 & 0.3x0.3x0.3 cm 3 In-house gamma analysis software Evaluation of AcurosXB deterministic algorithm for heterogeneous dose calculation in lung cancer with RPC thorax phantom Tao Han 1, Firas Mourtada 1,2, Roman Repchak 1, Jacqueline Tonigan 1, Justin Mikell 1, Rebecca Howell 1, Mohammad Salehpour 1, Andrea Molineu 1, and David Followill 1 1 Department of Radiation physics, UT MD Anderson Cancer Center; 2 Department of clinical physics, Helen F. Graham Cancer Center Table 1: Percentage differences of AAA, AXB_mm, and AXB_wm for TLD dose measurements in (a) IMRT and (b) RapidArc plan. Fig 3: Comparison of DVHs calculated by AAA, AXB_mm and AXB_mw for IMRT and RapidArc plans. Table 2: Percent of points passing gamma analysis with acceptability criteria of 5%3 mm. Table 3: The computation times of AAA and AXB for IMRT and RapidArc Plans. size do not improve the agreement to TLD data. Fig. 3 shows the distribution of gamma index with 5%/3mm criteria for first delivery of IMRT and RapidArc plans. The averaged gamma analysis for all three deliveries were summarized in Table 2. The AXB_mm gives the best agreement to film (all over 90%), while some of AAA predictions did not pass the 5%/3mm criteria. Fig.4 shows the comparison of DVH. Their differences are within 1% for normal tissue and 2% for PTVs. Table 3 shows the computation times. The AAA and AXB computation times were comparable for IMRT but AXB was 4-6 times faster than AAA for RapidArc plan. Results Table 1 shows the comparison between TLD measurements with the calculated dose from AAA, AXB_mw, and AXB_mm. All of AAA and AXB_mm are within 5% except for the RapidArc cord position; dose calculation with smaller grid Dose grid size: 0.1x0.1x0.1 cm 3 Dose grid size: 0.3x0.3x0.3 cm 3 AAAAXB_mwAXB_mm AAAAXB_mwAXB_mm IMRT plan RapidArc Note: percentage difference = (TLD-calculation)/TLD*100 Note: unit is in minutes Acknowledgements National Institutes of Health grant 2R44CA , CA and MDACC Support Grant CA IMRT TLD position Measure ment (cGy) Dose grid size 0.1x0.1x0.1 cm 3 Dose grid size 0.3x0.3x0.3 cm 3 AAAAXB_wmAXB_mmAAAAXB_wmAXB_mm PTV_Inf PTV_Sup Heart Cord RapidArc PTV_Inf PTV_Sup Heart Cord Film position Dose grid size: 0.1x0.1x0.1 cm 3 Dose grid size: 0.3x0.3x0.3 cm 3 AAAAXB_mw AXB_mm AAAAXB_mw AXB_mm a) IMRT plan Axial Sagittal Coronal b) RapidArc Axial Sagittal Coronal Fig 2: IMRT (left), RapidArc (right) plans and dose distributions in axial and sagittal views. Fig 1: Screen capture from Eclipse TPS depicting the RPC thorax phantom, structure contours (heart, lung, cord, PTV, film inserts), and one CT slice depicting the locations of TLD. Fig 3: Distribution of gamma index with a 5%/3mm criteria between film measurements to TPS calculations for IMRT (Fig 3.1) and RapidArc (Fig 3.2). Fig 3.1: IMRTFig 3.2: RapidArc AAA AXB_mm Axial Sagittal Coronal IMRT RapidArc