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 Followill1
1Department
of Radiation physics, UT MD Anderson Cancer Center; 2 Department of clinical physics, Helen F. Graham Cancer Center
Introduction
AAA
AAA
AXB_mm
Axial
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
Sagittal
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
AXB_mm
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
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.
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).
Dose grid size: 0.1x0.1x0.1 cm3
AAA
AXB_mw AXB_mm
a) IMRT plan
Axial
Sagittal
Coronal
b) RapidArc
Axial
Sagittal
Coronal
Dose grid size: 0.3x0.3x0.3 cm3
AAA
AXB_mw AXB_mm
89.2
90.4
91.5
95.1
91.1
96.7
95.7
91.4
96.1
89.9
90.5
91.6
95.2
92.1
96.5
95.6
92.8
96.2
87.2
88.3
89.5
91.6
92.2
94.2
92.1
92.6
94.5
87.6
88.9
89.7
91.8
92.4
94.1
92.4
92.9
94.7
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
Fig 2: IMRT (left), RapidArc (right) plans and dose distributions
• AXB 11.0.03
in axial and sagittal views.
• Dose-to-water in
medium (AXB_mw)
IMRT
• Dose-to-medium in
Measure
Dose grid size 0.1x0.1x0.1 cm Dose grid size 0.3x0.3x0.3 cm
TLD
medium (AXB_mm)
ment
position
AAA
AXB_wm AXB_mm
AAA
AXB_wm AXB_mm
• Clinically equivalent IMRT and PTV_Inf (cGy)
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
VMAT (RapidArc) plans were
Heart
175.0
3.8
3.3
3.1
4.3
4.0
4.2
generated on Eclipse
Cord
139.5
-2.8
-0.5
-0.5
-2.5
-0.4
-0.4
RapidArc
• 9 fields IMRT
PTV_Inf
598.0
-3.2
-0.1
-1.7
-4.0
-0.2
-2.2
• 2 arcs RapidArc
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
• Each plan delivered 3 times
98.7
-5.8
-3.8
-3.8
-6.4
-4.4
-4.4
• Dose grid sizes: 0.1x0.1x0.1 & Cord
Note: percentage difference = (TLD-calculation)/TLD*100
0.3x0.3x0.3 cm3
• In-house gamma analysis
Table 1: Percentage differences of AAA, AXB_mm, and AXB_wm
software
for TLD dose measurements in (a) IMRT and (b) RapidArc plan.
3
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.
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.
Acknowledgements
RapidArc
Fig 3: Comparison of DVHs calculated by AAA, AXB_mm and AXB_mw
for IMRT and RapidArc plans.
3
IMRT plan
RapidArc
Dose grid size: 0.1x0.1x0.1 cm3
AAA
AXB_mw AXB_mm
8.7
15.8
15.8
75
21.8
21.7
Dose grid size: 0.3x0.3x0.3 cm3
AAA
AXB_mw
AXB_mm
2.3
3.1
3.1
16
4.2
4.3
Note: unit is in minutes
Table 3: The computation times of AAA and AXB for IMRT and RapidArc
Plans.
National Institutes of Health grant
2R44CA105806-02, CA010953 and
MDACC Support Grant CA016672
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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
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