Results

1
Evaluation of the Effectiveness of Analytical
Anisotropic Algorithm in Flattened and
Flattening-Filter-Free Beams for High Energy Dose
Delivery Using the Radiological Physics Center
Lung Phantom R Repchak1, A Molineu1, R Popple3, S
Kry1, R Howell1, D Followill1

(1) MD Anderson Cancer Center,
Houston, TX, (2) University of Alabama at
Birmingham, Birmingham, AL,
Results The measured-to-predicted dose ratio
criteria used by the RPC to credential
institutions is 0.92-1.02, however for this work,
a criteria of 0.95-1.05 was used to compare the
measured results with the calculated doses. In
addition, the gamma index analysis criteria for
this work was set to be 5/3mm with 90 of the
average number of pixels passing this criteria.
All of the target measured-to-predicted dose
ratios fell within the 5 criterion. In
addition, all of the gamma analyses also met the
90 criterion even for the highest
energies. RPC Gamma index using 5/5mm
around 0.97 Care should be taken when
considering the RPC limits for energies higher
than 12 MV, since the original RPC criteria was
established based on the statistical analysis of
the large number of irradiations in 6-12 MV
range, its validity has not been verified for
energies greater than 12 MV. There was a
divergence in the measured profiles from the
calculated outside the PTV in superior-inferior
direction for all plans and beam energies. This
deviation represents an increased dose to the
tissues outside the planned treatment volume that
leads to a higher dose to a normal lung (by 4-5
of the prescribed dose on average) than what was
predicted by AAA calculation in the Eclipse
TPS.
Fig. 1 The RPC Lung phantom Fully assembled
phantom (top left) Phantom tumor, heart, and
spine inserts (top right) Axial slice of the
phantom CT scan (bottom left) Beam arrangements
used for planning in Eclipse TPS (bottom right).

• Dosimetry
• Four TLD capsules (two in the target, one in
  spine, and one in heart) and three orthogonal
  Radiochromic EBT2 films in axial, coronal, and
  sagittal planes were used to verify the accuracy
  of the dose delivered during each phantom
  irradiation
• Treatment Planning
• The CTV was equal to GTV and the PTV was created
  by expanding the CTV by 0.5 cm axially and by 1
  cm in superior-inferior direction
• AAA v.8.9.08 heterogeneity correction was applied
  for volume dose calculations in all plans
• A single fraction of 6 Gy was prescribed and
  normalized to at least 95 of the PTV
• Normal Tissues Constraints

Fig. 4 Summary for all plans Measured-to-predicte
d dose ratios (top) 2D Gamma index results using
5/3mm criteria (bottom)
Conclusion The results from both flattened and
flatted-filter-free plans in 6-10 MV range are in
a good agreement with the RPC data and show that
AAA algorithm is capable of calculating treatment
plans in a complex heterogeneous environment
consistently and accurately using 5/3mm gamma
index and 5 point dose criteria. This AGREES
with the existing recommendations of only using
photon beams energies of ?12 MV for lung
treatments. However, regarding the use of higher
photon energies for lung treatments, neither 15
MV or 18 MV are recommended to be used in
radiation therapy treatments of lung tumors due
to a larger penumbra (Wang et al) and potential
underdose of the tumor (Klein et al) which can
significantly compromise the effectiveness of the
radiation treatment and local tumor control. The
results from 15 MV and 18 MV plans calculated
using AAA delivered to the RPC anthropomorphic
lung phantom do not show a decreased dose to the
tumor and demonstrate a good agreement between
the calculated and delivered doses despite an
increased electronic lateral disequilibrium and a
larger penumbra for higher energies. Our
evaluation of the AAA heterogeneity corrected
dose calculations using the RPC lung phantom
DISAGREES with the recommendation to only use ?12
MV for lung treatments, specifically for the AAA
algorithm.
Fig. 2 Deviation of measured dose profiles from
the calculated in superior-inferior direction
References 1) L. Wang, E. Yorke, G. Desobry, and
C. Chui, Dosimetric advantage of using 6 MV over
15 MV photons in conformal therapy of lung
cancer Monte Carlo studies in patient
geometries, Journal of Applied Clinical Medical
Physics 3 (1), 51-59 (2002) 2) E. Klein, A.
Morrison, J. Purdy, M. Graham, and J. Matthews,
A volumetric study of measurements and
calculations of lung density corrections for 6
and 18 MV photons, Int. J. Radiat. Oncol.,
Biol., Phys. 37, 11631170 (1997)
This investigation was supported by PHS grants
CA10953 and CA81647 awarded by the NCI, DHHS.
Fig. 3 Change in measured-to-predicted dose ratio
with the beam energy
2
Title of the Poster Presentation Goes
Here Authors of the Poster Presentation Goes
HereInstitutional and/or Graduate School of
Biomedical Sciences Affiliation Goes Here