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

1

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
AAA
AXB_mm
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).
Film position   Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3   Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3
Film position   AAA AXB_mw AXB_mm   AAA AXB_mw AXB_mm
a) IMRT plan                
Axial   89.2 95.1 95.7   89.9 95.2 95.6
Sagittal 90.4 91.1 91.4 90.5 92.1 92.8
Coronal   91.5 96.7 96.1   91.6 96.5 96.2
b) RapidArc                
Axial   87.2 91.6 92.1   87.6 91.8 92.4
Sagittal   88.3 92.2 92.6 88.9 92.4 92.9
Coronal   89.5 94.2 94.5   89.7 94.1 94.7
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 53 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

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.
IMRT IMRT IMRT IMRT IMRT IMRT IMRT IMRT
TLD position Measurement (cGy) Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3
TLD position Measurement (cGy) AAA AXB_wm AXB_mm AAA AXB_wm AXB_mm
PTV_Inf 642.8 -4.3 -1.6 -2.6 -4.0 -1.1 -2.4
PTV_Sup 642.0 -4.5 -1.6 -2.7 -4.2 -1.4 -2.4
Heart 175.0 3.8 3.3 3.1 4.3 4.0 4.2
Cord 139.5 -2.8 -0.5 -0.5 -2.5 -0.4 -0.4
RapidArc RapidArc RapidArc RapidArc RapidArc RapidArc RapidArc RapidArc
PTV_Inf 598.0 -3.2 -0.1 -1.7 -4.0 -0.2 -2.2
PTV_Sup 604.0 -2.7 0.5 -0.9 -2.5 1.0 -0.8
Heart 87.7 -5.3 -1.1 -2.5 -5.6 -0.8 -2.7
Cord 98.7 -5.8 -3.8 -3.8 -6.4 -4.4 -4.4
  Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3 Dose grid size 0.1x0.1x0.1 cm3   Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3 Dose grid size 0.3x0.3x0.3 cm3
  AAA AXB_mw AXB_mm   AAA AXB_mw AXB_mm
IMRT plan 8.7 15.8 15.8 2.3 3.1 3.1
RapidArc 75 21.8 21.7 16 4.2 4.3
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)/TL
D100
Table 1 Percentage differences of AAA, AXB_mm,
and AXB_wm for TLD dose measurements in (a) IMRT
and (b) RapidArc plan.