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Choreographing couch, collimator

an gan ry mo on n ra a on

deliverCollaboration of the following people at MSKCC:

Pengpeng Zhang

Yingli YangGig Mageras

Margie Hunt

Jian in Xion

Jie Yang

Maria Chan

Josh Yamada


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in VMAT for paraspinal SBRT

2nd

project was Choreographing couch,

VMAT


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Collimator trajectory in VMAT for paraspinal SBRT

Motivation

Improve dosimetric qualityo Increase target coverage

o

Preserve better critical organ sparing

Explore additional mechanical freedom

IJROBP. 2010; 77(2):591-9.


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Optimize collimator trajectory based on

S nchronize collimator rotation with MLC

motion, gantry rotation, and dose rate

modulation

Development and evaluation in paraspinal


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Why collimator matters?


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Determine collimator trajectory via


principle component analysis


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Paraspinal SBRT study

1.Retrospective study following

MSKCC paraspinal SBRT protocol

2.Prescription dose: 24Gy to tumor,

cord maximum dose


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All protocol constraints are met with all three plans


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Dosimetr Results:


Coll-VMAT vs VMAT vs IMRT


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-


Again, Why collimator angle

ma ers


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e uce w

Technique Average MUs

Coll VMAT 5164

VMAT 4868

IMRT 13283


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ummary

Coll-vmat provides an additional degreeof freedom

Dosimetric quality of VMAT plans is as

good or better as fixed gantry IMRT forparaspinal SBRT

ord dose lower with oll VMAT than

IMRT


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Choreographing couch,

gantry and collimator

We develo ed a software to facilitate the selection and

optimization of non-coplanar VMAT arcs

e eva ua e e ec n que n e rea men o

tumors

IJROBP. 2011; 80(4):1238-47


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Selecting couch/gantry trajectory

PTVEye

based on PTV/OAR areaoverlap

Brainstem

Cord

cLgcL ,,

i OARiPTVi

i

gcAgcA ,,

,


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Target/OAR Overlap Map

CA=-

60;

GA=-60

CA=45;

GA=100for particular patient

CA=0;

GA=-150

CA=85;GA=60


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Optimization of Couch/gantry Trajectory

,those with minimum overlap score.

Algorithm must remove combos in the forbidden zone collisions areas

Link and extend small arcs to create lon er arcs

Smooth arcs to accommodate mechanical constraints and limitations


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Adding optimized Collimator Trajectories

137o

80o


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Non-coplanar VMAT Delivery Using


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NS Radiotherapy Planning & Comparison

Ten CNS cases, fourteen tumors, three with dose painting,

Treatment techniques

IMRT: 4-6 non-coplanar beams

VMAT: 1-4 arc pairs (orthogonal collimator trajectories)

Std-VMAT: static couch and collimator

Tra-VMAT: d namic couch and collimator

Evaluate:

arge coverage

maximum/mean dose to OARs.


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Plan EvaluationTra Vmat

an ar


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TraTra--VMAT vsVMAT vs IMRT vs StdIMRT vs Std--VMATVMAT

Tra-VMAT Std-VMAT IMRT

PTV Dmin 94.1 16.4% 93.1 17% 87.9 18.1%

ra ns em mean . . . . . .

Chiasm Dmax 76.9 35.8% 78.5 36% 78.2 35.9%Chiasm Dmean 61.6 34.1% 64.2 34.1% 65.9 34.1%

Optical nerve Dmax 57.1 33.3% 59.4 32.3% 63.4 30.6%

Cochlea Dmax 50.9

39.7% 52.3

38.9% 59.3

33.7%mean . . . . . .

MU 614 419 622 446 1262 783

ra n cm Brain V70%(cm3) 173 71 200 91 163 72

(medianSTD)


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SummarySummary

Tra-VMAT vs IMRT

Higher PTV minimum dose, lower dose to brainstem,chiasm, optical nerve, and cochlea

improved treatment efficiency (by 50%)

Tra-VMAT vs Std-VMAT Better target conformality (ie lower brain dose)

Lower dose to brainstem, chiasm, and optical nerve

Superior mechanical flexibility of TrueBeam transforms to

better plan quality


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Future endeavors at our intuition

1) Jaw tracking change jaws per control point

A) To reduce leakage between parked leaves in VMAT

delivery.

B) To reduce the need to split IMRT beams

2) Target motion tracking

A) Collimator trajectory to aid MLC target tracking.

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