very high energy electrons 1. vhee as a legitimate ... · beams – single broad and narrow beam...
TRANSCRIPT
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Very High Energy Electr ons(VHEE) and 4D IMRT
Lech Papiez, Indiana University
VHEE and 4D IMRT- Issues and perceptions
1. VHEE as a legitimate alternative to photonbeam therapy.
2. Definite 4D IMRT in radiation therapy.3. Obstacles in delivering true 4D IMRT with
existing technology.4. Fast scanning of pencil beam VHEE as a
vehicle for 4D IMRT.
Dose for basic arrangement of VHEEbeams – single broad and narrow beam
150 MeV
Comparison of dose from singlebeamlets - VHEE vs. photons
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Comparison of ratio of target to integraldose from parallel opposed beamlets
T T
Comparison of penumbra for singleand parallel opposed beams
Penumbra (measured as the dis tance between 90% and 20% of dose maximu m ata given dep th) for single and parallel opposed electr on and pho to n beams.
Message I• Parameters (depth of beam penetration,
penumbra, integral dose) of basic VHEE beamarrangements are adequate for dosedistribution shaping for 3D conformal therapyand IMRT therapy.
• VHEE beam properties suggest advantage intheir clinical utilization due to their better ratio ofdose to target vs. integral dose.
• Potential shortcomings of VHEE (surface dose,photoneutrons).
Exploring potential advantage –case 1VHEE multi-energy (50,100,150, 200,
250 MeV) optimal planning
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20
30
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50
60
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100
Prostate model case
Optima l VHEE planfrom nine coplanar beams
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-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4-2
-1
0
1
2
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Tissue TissueBone
cm
cm
0.90.8
200 MeVTissue Air
0.5 0.7
-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4-2
-1
0
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cm
cm
0.9
0.80.7
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15 MVTissue Air
Exploring potential advantage –case 2Air-water interface : VHEE vs. x-ray
Radiusof air cavity = 2 cm
Isodoseline step5% ofmaximum dose
Advantages of VHEE therapy vs.photon therapy
Message II• VHEE provide potential advantages over photon
therapy by avoidance of electronic disequilibriumand dose variation at tissue interfaces
• VHEE provide potential advantages over photontherapy due to their more favorable ratio of dosedelivered to the target vs. integral dose delivered tothe body
• VHEE can be particularly effective if wholespectrum of electron beam energies will beavailable for treatment and if VHEE therapy can beeffectively integrated with photon beam therapy
Message III• VHEE based treatments avoid high dose at
surface for multiple beam arrangements
• VHEE based treatments provide negligibledose equivalent enhancement fromphotoneutrons and induced radioactivity
• VHEE based treatments require shieldingcomparable to 50 MeV electron or photontreatments
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VHEE advantage in 4D IMRTdue to the feasibili ty of fas t,electromagnetic scann ing of
VHEE pencil beams
3D IMRT – prin ciple (join t optimization forintensity maps over all beams)
T
Beam AP
Beam LAT
OAR 1
OAR 2
Beam AP
Beam LAT
1
10
0
4D IMRT - mov ing organs (phase I)
T
Beam LAT
Beam AP
OAR 1
OAR 2
OAR 3
OAR 4
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1
00
00
OAR 2
OAR 3
4D IMRT – movi ng organ s (phas e 2)
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OAR 1
OAR 4
Beam AP
Beam LAT0
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4D IMRT – principle (join t optimi zation forintensi ty maps over all beams and phases)
Phase I
Phase II
Beam AP Beam LAT
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0
0 0 00
0 0 0 0.50.5
4D IMRT vs. 3D IMRT - I
• Best possible 3D plan requires optimizationthat involves search for beamlet intensities thatcover jointly all beam dire ctions
• Best possible 4D plan requires optimizationthat involves search for beamlet intensities thatcover jointly all beam dire ctions and all bodygeometries
• No 3D plan for any stationa ry geometry can,under general cond ition s, achieve asfavora ble dose crit eria as 4D plan optimizedsimu ltaneou sly for all body geometries
4D IMRT vs. 3D IMRT – II• Notice the similarity
– The optimal plan for stationary body, as well as for movingbody, requires evaluation of criteria for dose distributionaccumulated over all time of body exposure
• Notice the difference– The delivery of optimal 4D plan requires proper redistribution
of beamlet intensities over all geometries of the treated body– this is equivalent to realization of black and white“intensity” movie for each beam (TV therapy).
– In contrast, the optimal 3D plan requires only properaccumulation of beamlet intensities for each beam over theentire interval of irradiation – this is equivalent to realizationof black and white “intensity” (still) picture for each beam.
Geom
etry4
Geom
etry2
Beam angle 4Beam angle 2 Beam angle 3
Geom
etry3
Optim
izationcriteria
forG
eometry
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Beam angle 1
One phase planning (single 3D) –cases (i) and (ii)
Gatin
g
Mo
tion
do
seartifacts
Mo
tion
do
seartifacts
Mo
tion
do
seartifacts
Mo
tion
do
seartifacts
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Optim
izationcriteria
forG
eometry
4
Optim
izationcriteria
forG
eometry
2
Beam angle 4Beam angle 2 Beam angle 3
Optim
izationcriteria
forG
eometry
3
Optim
izationcriteria
forG
eometry
1
Beam angle 1
Separate phase planning (multi 3D) –case (iii)
Gatin
gG
ating
Gatin
gG
ating
Geom
etry4
Geom
etry2
Beam angle 4Beam angle 2 Beam angle 3
Geom
etry3
Geom
etry1
Beam angle 1
Separate phase planning on 4Dgeometry (3.5 D) – case (iv)
Optim
izationcriteria
forreference
geometry
Gatin
gG
ating
Gatin
gG
ating
Geom
etry4
Geom
etry2
Beam angle 4Beam angle 2 Beam angle 3G
eometry
3
Beam angle 1
True 4D planning and delivery –case (v)
Geom
etry1
Geom
etry2
Geom
etry3G
eometry
4
Optim
izationcriteria
forreference
geometry
Fast
scann
ing
Towards 4D IMRT with DMLC delivery– what can be gained?
• Plan for single phase (3D)• Target moving and OAR immobile• DMLC delivery basic goal is to impose the planned
intensity map over the target• Non-uniqness of the solution for DMLC to moving
target allows to reduce the dose to OAR• Passive solutions through DMLC motion correlation
with phase of target shift• Active solution with the modification of leaf velocities
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IMRT to moving target andstationary organ at risk (OAR)
Increase of dose to OAR for adversecorrelation of OAR and leaf motion
Leading Leaf
Following Leaf
Sensitive Organ
TargetPoints
Time (s)
Integral Intensity Intended = 6.0 MUIntegral Intensity Delivered = 21.0 MU� 250% increase in integral monitor units
Intensi tydeliver ed
to the target
Intensity delive redto OAR
Reduction of dose to OAR for “good”correlation of OAR-leaf motions
Leading Leaf
Following Leaf
Sensitive Organ
TargetPoints
Integral intensity from plan = 6.0 MUIntegral intensity delivered = 3.67 MU40% reduction of intensity delivered
Time (s)
Inten sit y delive redto the target
Intensity deliveredto OAR
DMLC IMRT for 4D therapy –statistical analysis
Integ
ralMU
toO
AR
Phase Shi ft (radian s)
Average
Intended
OAR
TargetAdverse phase correlation
“good” phase correlation
Intensity planned and deliveredto target
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LeadingLeaf
Following Leaf
Sensitive Organ
TargetPointsUnmodifiedTrajectories
Pos
itio
n(L
abra
me
ofre
fere
nce)
Ti me (s)
Static Geometry
Modified (Case2)
Unmodified(Case1)
82% reduction in integral MU from static case74% reduction in integral MU relative case 1
Partial 4D IMRT can provide generousreduction of dose to OAR
Conclusions
• VHEE therapy is a feasible alternative tophoton and proton therapy (for sometreatments VHEE is dosimetrically superior tophoton therapy)
• True 4D IMRT treatment delivery isequivalent to creation of black and whitemovie displayed on the screen of each beamfield
• VHEE electromagnetic scanning of electronpencil beam provides the physically viabletool for delivery of the true 4D IMRT
Acknowle dgme nts
• Vadim Moskvin, Colleen DesRosiers (IU-simulation, evaluation and planning for VHEE)
• George Sandison, Colin Yeboach (TBakerCC –optimized VHEE IMRT vs. photons andprotons)
• Malka et al (CNRS, Ecole Polytechnique,Palaiseau, France–laser based VHEE, emshaped VHEE beams)
• Thomas Bortfeld – critique and discussion• Dharani Rngaraj, Ryan McMahon (IU, WashU –
DMLC IMRT for moving targets and OAR)