A dosimetric comparison of IMRT vs VMAT optimization in
early stage whole breast cancer
Nader Moshiri
Professional Science Masters in Medical Physics
Physics Department, Florida Atlantic University
Outline
• Purpose
• Introduction
• Method
• Results
• Summary
• Work to be done
• Acknowledgements
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Purpose
To compare the dose to organs at risk (OAR) while using VMAT vs IMRT techniques for early breast cancer.
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Introduction • VMAT (Volumetric Modulated Arc Therapy), formally known
as Intensity Modulated Arc Therapy (IMAT), was first introduced by Dr. Cedric Yu in 1995.
• Elekta PreciseBeam Infinity
• Varian RapidArc
• Philips SmartArc
• RapidArc adjusts not only the treatment aperture, but also the rotational speed of the gantry and the delivery dose rate.
• VMAT usage is growing very fast for various tumors, e.g. prostate, head & neck, pelvis, lungs, GYN as well as breast cancer!
• Nothing on vendor ‘s website about VMAT for breast tumor! 5
Method
• Tangent IMRT (forward plan), breath hold (Phase I).
• A retrospective study over 25 whole left breast patients’ plans (7 RapidArc plans & 18 Tangent IMRT).
• Eclipse v 11.0.47 was used to create the alternative plans for each case using the same CT images, contours, energy(6X), Linac and normalization.
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Method Cont’d
• The prescription dose to planning target volume (PTV) was 50 Gy in 25 fractions.
• All plans were normalized such that 100% of the dose covered 95% of PTV.
• All plans were acceptable based on the RTOG1005 constraints.
• Maximum 3 Arcs were applied.
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Null Hypothesis 𝐻0: μ1= μ2 ; the mean doses of the two modalities are equal.
• Two-tail t-test was applied for unequal variances.
• All p-values were calculated for α = 0.05 and confidence interval of %95.
• If p ≤ 0.05 the means are significantly different therefore the null hypothesis is rejected.
• If p > 0.05 the means are not significantly different thus the null hypothesis is valid.
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Results
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Organs Limits IMRT VMAT p-values
RTOG 1005
ideal accepted
Ipsilateral
Lung
V5 22.94 74.37 < 0.0001 <50% <55%
V10 15.67 39.92 < 0.0001 <35% <40%
V20 11.92 14.99 0.0175 <15% <20%
V30 10.11 6.52 0.0018
Dmin(Gy) 0.16 1.15 < 0.0001
Dmax(Gy) 52.19 47.26 < 0.0001
Dmean(Gy) 7.10 11.27 < 0.0001
Contralateral
Lung
V5 0.00 1.77 0.0016 <10% <15%
Dmin(Gy) 0.00 0.55 < 0.0001
Dmax(Gy) 1.28 7.51 < 0.0001
Dmean(Gy) 0.08 2.08 < 0.0001
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Results cont'd Organs Limits IMRT VMAT p-values
RTOG 1005
ideal accepted
Heart
V10 4.22 9.15 0.0394 <30% <35%
V25 2.74 0.00 0.0005 <5%
D33% 1.65 5.85 < 0.0001
Dmin(Gy) 0.20 1.75 < 0.0001
Dmax(Gy) 48.66 21.64 < 0.0001
Dmean(Gy) 2.78 7.42 0.0328 <4 <5
Contralateral
Breast
V5 0.01 8.38 < 0.0001
D5% 0.96 5.52 < 0.0001
Dmin(Gy) 0.00 0.53 < 0.0001
Dmax(Gy) 6.15 10.68 0.0217 <3 <3.3
Dmean(Gy) 0.21 2.40 < 0.0001
PTV (L Breast)
Conformity Index 1.30 1.03 0.0003
Planning time 4min 22min 0.0081
MU 403.56 689.28 < 0.0001
Dmin% 65.29 68.44 0.6591
Dmax% 112.33 114.90 0.0787 <115% <120%
Dmean% 106.14 102.00 0.2302
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0
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ean
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contralateral lung contralateralbreast
heart ipsilateral lung PTV (left breast)
IMRT
VMATGy
Dose to organs
Summary
• The dose-volumetric results of Tangent IMRT vs RapidArc were significantly different for most of the constraints, although all plans were made within the threshold values recommended by RTOGs.
• Mean doses to left lung, heart, right lung and right breast were significantly different in RapidArc from Tangent IMRT plans, especially for heart!
• Tangent IMRT treatment delivery utilized less total monitor units (MU) than RapidArc (mean of 403.56 vs 689.28 respectively).
• Conformity index was significantly different for the two modalities (1.3 for IMRT vs 1.03 for VMAT).
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Work to be done
• Multi field IMRT (inverse plan) with PTV including axillary nodes (in progress).
• Gain access to a multi-criteria optimization program to compare the doses to OARs and compare with our results.
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Acknowledgements Special thanks to:
• Silvia Pella, PhD, DABR for providing me an easily accessible environment and non-stop support!
• Th. Leventouri, PhD, PSMMP program Director for all her work for our young program.
• Thomas Costantino and David Littlejohn CMDs at SFRO for helping with this research.
• South Florida Radiation Oncology (SFRO) for providing the facilities.
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