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Evaluation of AcurosXB deterministic algorithm for heterogeneous dose calculation in lung cancer with RPC thorax phantom

Tao Han1, Firas Mourtada1,2, Roman Repchak1, Jacqueline Tonigan1, Justin Mikell 1, Rebecca Howell1, Mohammad Salehpour1, Andrea Molineu1, and David Followill11Department of Radiation physics, UT MD Anderson Cancer Center; 2 Department of clinical physics, Helen F. Graham Cancer Center

AAA

AXB_mm

AAA

AXB_mm

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).

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.

Axial

Sagittal

Coronal

Fig 3.1: IMRT

Fig 3.2: RapidArc

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).

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.

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.

Table 2: Percent of points passing gamma analysis with acceptability criteria of 5%3 mm.

IMRT

- Methods & Materials
- RPC thorax phantom
- 4 TLD tublets
- 3 EBT2 films (axial,sagittal, coronal)

- Varian Eclipse TPS 11.0
- AAA 10.0.24
- AXB 11.0.03
- 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 cm3
- In-house gamma analysis software

- RPC thorax phantom

Acknowledgements

National Institutes of Health grant 2R44CA105806-02, CA010953 and MDACC Support Grant CA016672

RapidArc

Fig 2: IMRT (left), RapidArc (right) plans and dose distributions in axial and sagittal views.

References

1.Wareing, T., J. Morel, and J. McGhee, Coupled electron-photon transport methods on 3-D unstructured grids. Trans Am Nucl Soc, 2000. 83: p. 240-242.

2.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, 2008. 35(6): p. 2279-85.

3. 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. 2010. 55, 581-598

4. 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, 2011. 38. 2651-2663

Fig 3: Comparison of DVHs calculated by AAA, AXB_mm and AXB_mw for IMRT and RapidArc plans.

Note: unit is in minutes

Table 3: The computation times of AAA and AXB for IMRT and RapidArc Plans.

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

Note: percentage difference = (TLD-calculation)/TLD*100

Table 1: Percentage differences of AAA, AXB_mm, and AXB_wm for TLD dose measurements in (a) IMRT and (b) RapidArc plan.

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