Yue Yan, Daniel Saenz, Poonam YadavProf. Bhudatt Paliwal

� Background

� Method and materials

� Study cancer sites

• Prostate

• Head & neck

• Lung

� Discussion and summary

� Questions and answer

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� Motivations for flattening filter free (FFF) beams :

� Pros:▪ Greatly increase dose rate[1-5] (600 MU/min->1400 MU/min (2400 MU/min) for

6X (10X) beam for Varian TrueBeam system) decreased treatment time. More

obvious in treatment modalities requiring large MUs (e.g. SBRT, SRS).

▪ Large decrease in external scatter from the gantry head and lower leakage

dose [5] which may benefit the dose sparing effect to OARs[6].

▪ Greatly reduced neutron contamination to patient when using high energy

beam for treatment[7].

▪ Reduced uncertainty in dose calculation caused by scatter from flattening

filter[1].

� Cons for FFF Beams:▪ Soft spectrum tends to give lower mean dose for PTV coverage[1]. It also tends

to increase internal scatter[8] which may compromise the dose sparing effect to

OARs.

▪ High dose rate delivery is more sensitive to patient’s motion[9].

� Beam commissioning of TrueBeam (Varian, CA) system is completed in Eclipse

treatment planning system(Version 10)

� Energies: 6X and 10X

� Beam modalities: both FFF and flattened (Conv.) beams

� Identical optimal objectives and parameters (e.g. field size, energy, etc.) are used to

design the plan

� VMAT and static IMRT are used to design the plan

� Data Matrix[10]:

� Conformity index:�

� Target coverage: �

� Conformity number: �

� Gradient index: �

� Be Close to unity means better dose distribution for all data matrix elements

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� Dose description:

• ,

� Optimal objectives:

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Optimization objectives of VMAT & Static IMRT for prostate cancer

StructureType of

constraint Volume(%) Dose(Gy) Priority

Prostate PTV lower 100 78 100

Prostate PTV upper 0 78 100

Penile bulb upper 40 50 50

Left hip upper 0 45 50

Hot upper 0 39 50

Bladder upper 30 50 50

Rectum upper 30 50 50

SV PTV-Prostate lower 100 70.2 100

SV PTV-Prostate upper 20 72 100

SV PTV-Prostate upper 0 78 100

Right hip upper 0 45 50

Rectum Avoid upper 0 78 50

� VMAT plan:• One arc• 6X beam

• 10X beam

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� VMAT plan:

• 6X beam

• 10X beam

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Prostate PTV

Without filter With filter p for DVH comparison

Minimum dose (Gy) 70.72 71.42

p<0.001

Maximum dose (Gy) 81.99 82.05

Mean dose (Gy) 78.45 78.36

Conformity index (CI) 1.08 1.06

Target Coverage (TC) 1.00 1.00

Conformity number (CN) 0.93 0.94

Gradient index (GI) 6.24 7.12

Prostate PTV

Without filter With filter p for DVH comparison

Minimum dose (Gy) 70.94 70.45

p<0.001

Maximum dose (Gy) 81.96 82.83

Mean dose (Gy) 78.50 78.39

Conformity index (CI) 1.08 1.06

Target Coverage (TC) 1.00 1.00

Conformity number (CN) 0.93 0.94

Gradient index (GI) 6.08 6.30

� VMAT: dose ratio

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6X

10X

Body Rectum Avoid Penile Bulb L Hip R Hip Rectum Bladder

Integral dose

ratio (FFF/Conv.) 0.93 1.00 0.74 0.96 0.92 0.98 0.97

Maximum dose

ratio (FFF/Conv.) 1.01 1.00 0.90 1.02 0.92 1.00 1.00

Body Rectum Avoid Penile Bulb L Hip R Hip Rectum Bladder

Integral dose

ratio (FFF/Conv.) 0.99 1.00 0.88 0.98 0.94 0.99 1.00

Maximum dose

ratio (FFF/Conv.) 1.00 1.01 0.91 1.02 0.91 1.01 1.02

Ratio less than unity is preferred.

� Static IMRT 6X & 10X

• 5 coplanar beams

• 6X

• 10X

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� Static IMRT:

• 6X

• 10X

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Prostate PTV

Without filter With filter p for DVH comparison

Minimum dose (Gy) 68.99 69.30

p<0.001

Maximum dose (Gy) 75.46 78.85

Mean dose (Gy) 75.46 75.70

Conformity index (CI) 1.51 1.31

Target Coverage (TC) 0.81 0.85

Conformity number (CN) 0.54 0.65

Gradient index (GI) 15078.62 2485.80

Prostate PTV

Without filter With filter p for DVH comparison

Minimum dose (Gy) 69.25 70.01

p<0.001

Maximum dose (Gy) 78.94 79.52

Mean dose (Gy) 76.51 76.95

Conformity index (CI) 1.07 1.11

Target Coverage (TC) 0.89 0.93

Conformity number (CN) 0.83 0.83

Gradient index (GI) 80.18 64.30

� Static IMRT:

• 6X

• 10X

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Body Rectum Avoid Penile Bulb L Hip R Hip Rectum Bladder

Integral

dose ratio (FFF/Conv.) 1.01 1.00 0.94 0.99 0.99 0.99 1.02

Maximum

dose ratio (FFF/Conv.) 1.00 1.00 0.94 1.01 1.02 1.00 1.00

Body Rectum Avoid Penile Bulb L Hip R Hip Rectum Bladder

Integral

dose ratio (FFF/Conv.) 1.00 0.99 0.90 0.98 0.98 0.99 1.01

Maximum

dose ratio (FFF/Conv.) 0.99 0.99 0.92 0.99 0.99 0.99 1.00

Ratio less than unity is preferred.

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Back

VMAT plan

Static IMRT plan

� Dose description:• ,

� Optimal objectives:

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Optimization objectives of VMAT & static IMRT for head & neck cancer

StructureType of

constraint Volume(%) Dose(Gy) Priority

PTV 66 upper 0 66 100

PTV 66 lower 100 66 100

PTV 56-PTV 66 upper 20 60 100

PTV 56-PTV 66 upper 0 66 100

PTV 56-PTV 66 lower 100 56 100

Esoph 3 upper 0 20 50

PTV nodes 66 upper 0 67 100

PTV nodes 66 lower 100 66 100

Cord exp upper 0 40 90

Esoph 2 upper 0 35 50

� VMAT: • one arc

• 6X

• 10X

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� VMAT:

• 6X

• 10X

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PTV 66

Without filter With filter p for DVH comparison

Minimum dose (Gy) 60.70 60.77

p<0.001

Maximum dose (Gy) 70.75 69.97

Mean dose (Gy) 66.98 66.90

Conformity index (CI) 1.28 1.26

Target Coverage (TC) 1.00 1.00

Conformity number (CN) 0.78 0.79

Gradient index (GI) 7.97 8.46

PTV 66

Without filter With filter p for DVH comparison

Minimum dose (Gy) 56.30 55.74

p=0.91

Maximum dose (Gy) 71.61 71.37

Mean dose (Gy) 67.13 67.13

Conformity index (CI) 1.28 1.28

Target Coverage (TC) 0.99 0.99

Conformity number (CN) 0.77 0.77

Gradient index (GI) 7.94 8.37

� VMAT:

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6X

10X

Body Brain StemBrain Stem

Exp L Parotid R Parotid Cord Esophagus

Integral dose

ratio (FFF/Conv.) 0.96 0.82 0.82 0.90 0.90 0.99 1.02

Maximum

dose ratio (FFF/Conv.) 1.01 0.81 0.81 1.00 0.97 1.02 1.00

Body Brain StemBrain Stem

Exp L Parotid R Parotid Cord Esophagus

Integral dose

ratio (FFF/Conv.) 0.95 0.75 0.75 0.92 0.86 0.99 1.03

Maximum

dose ratio (FFF/Conv.) 1.00 0.73 0.73 0.97 1.00 1.01 1.01

Ratio less than unity is preferred.

� Static IMRT: � 7 coplanar beams

• 6X

• 10X

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� Static IMRT:

• 6X

• 10X

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PTV 66

Without filter With filter p for DVH comparison

Minimum dose (Gy) 59.00 60.33

p<0.001

Maximum dose (Gy) 69.47 70.35

Mean dose (Gy) 66.62 67.80

Conformity index (CI) 1.24 1.32

Target Coverage (TC) 0.99 1.00

Conformity number (CN) 0.81 0.76

Gradient index (GI) 11.51 8.54

PTV 66

Without filter With filter p for DVH comparison

Minimum dose (Gy) 58.96 59.85

p<0.001

Maximum dose (Gy) 69.39 69.65

Mean dose (Gy) 66.96 67.97

Conformity index (CI) 1.23 1.30

Target Coverage (TC) 0.99 1.00

Conformity number (CN) 0.81 0.77

Gradient index (GI) 10.13 8.27

� Static IMRT:

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Body Brain StemBrain Stem

Exp L Parotid R Parotid Cord Esophagus

Integral dose

ratio (FFF/Conv.) 0.96 0.82 0.82 0.90 0.90 0.99 1.02

Maximum

dose ratio (FFF/Conv.) 1.01 0.81 0.81 1.00 0.97 1.02 1.00

6X

Body Brain StemBrain Stem

Exp L Parotid R Parotid Cord Esophagus

Integral dose

ratio (FFF/Conv.) 0.97 0.85 0.84 0.92 0.93 0.99 0.98

Maximum

dose ratio (FFF/Conv.) 0.99 0.79 0.79 0.98 0.98 0.97 0.97

10X

Ratio less than unity is preferred.

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Back

VMAT Plan

Static IMRT Plan

� Dose description:

• ,

� Optimal objectives:

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Optimization objectives of IMRT 6X and 10X

StructureType of

objective Volume(%) Dose (Gy) Priority

Ptv 60 exp lower 100 60 100

PTV 60 Lung upper 0 62 120

Body upper 0 30 80

Cord exp upper 0 40 90

Esophagus upper 40 30 100

Lung-CTV upper 25 20 50

Lung-CTV upper 18 30 50

PTV 50 node upper 20 55 100

PTV 50 node lower 100 50 100

PTV 50 node upper 0 60 100

� Static IMRT:• 9 beams 6X

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Conv. Beam

FFF. Beam

� Static IMRT:

• 6X

• 10X

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� Static IMRT:

• 6X

• 10X

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PTV 60 Lung

Without filter With filter p for DVH comparison

Minimum dose (Gy) 31.14 33.71

p<0.001

Maximum dose (Gy) 64.75 66.65

Mean dose (Gy) 59.17 60.67

Conformity index (CI) 1.09 1.10

Target Coverage (TC) 0.86 0.98

Conformity number (CN) 0.79 0.89

Gradient index (GI) 10.96 4.80

PTV 60 Lung

Without filter With filter p for DVH comparison

Minimum dose (Gy) 33.386 35.68

p<0.001

Maximum dose (Gy) 65.467 66.48

Mean dose (Gy) 60.017 61.33

Conformity index (CI) 1.06 1.10

Target Coverage (TC) 0.93 0.98

Conformity number (CN) 0.88 0.89

Gradient index (GI) 5.92 3.76

Static IMRT:

6X

10X

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Carina Esophagus Cord Heart Lungs L Lung R Lung Lung-CTV

Integral dose

ratio (FFF/Conv.) 0.97 0.96 0.95 0.94 0.96 0.96 0.97 0.96

Maximum

dose ratio (FFF/Conv.) 0.97 0.97 0.96 0.97 0.97 0.97 0.97 0.97

Carina Esophagus Cord Heart Lungs L Lung R Lung Lung-CTV

Integral dose

ratio (FFF/Conv.) 0.98 0.96 0.94 0.91 0.96 0.96 0.97 0.96

Maximum

dose ratio (FFF/Conv.) 0.98 0.98 0.95 0.94 0.96 0.97 0.96 0.97

Ratio less than unity is preferred.

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� FFF beam usually can provide comparative treatment

plan with improved dose sparing effect to ORAs.

� However, the soft spectrum of FFF beam lead to lower

mean dose for target coverage, which may need extra

consideration in treatment plan.

� Density inhomogeneity in PTV is an important factor to

influence both PTV coverage and sparing effect to

OARs for FFF beam and it may lead to unacceptable

PTV coverage for FFF beam.

� Completely removing flatten filter may NOT be optimal.

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of flattening filter free photon beams. Med Phys 38(3):1280-1293.

� [2] Huang YF, Siochi RA, Bayouth JE.(2012) Dosimetric properties of a beam

quality-matched 6 MV unflattened photon beam. J Appl Clin Med Phys 13(4):71-81.

� [3] Vassiliev ON, Titt U, Kry SF, Pönisch F, Gillin MT and Mohan R. (2006) Monte

Carlo study of photon fields from a flattening filter-free clinical accelerator. Med Phys

33(4):820-827.

� [4] Reggiori G, Mancosu P, Castiglioni S, Alongi F, Pellegrini C, Lobefalo F, Catalano

M, Fogliata A, Arcangeli S, Navarria P, Cozzi L and Scorsetti M. (2012) Can

volumetric modulated arc therapy with flattening filter free beams play a role in

stereotactic body radiotherapy for liver lesions? A volume-based analysis. Med Phys

39(2):1112-1118.

� [5] Titt U, Vassiliev ON, Pönisch F, Dong L, Liu H and Mohan R.(2006) A flattening

filter free photon treatment concept evaluation with Monte Carlo. Med Phys

33(6):1595-1602.

� [6] Kry SF, Vassiliev ON and Mohan R.(2010) Out-of-field photon dose following

removal of the flattening filter from a medical accelerator. Phys Med Biol 55 2155-

2166.

� [7] Kry SF, Howell RM, Titt U, Salehpour M, Mohan R and Vassiliev ON. (2008)

Energy spectra, sources, and shielding considerations for neutrons generated by a

flattening filter-free Clinac. Med Phys 35(5):1906-1911.

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� [8] Chofor N, Harder D. Willborn KC and Poppe B. (2011) Internal scatter, the

unavoidable major component of the peripheral dose in photon-beam radiotherapy.

Phys. Med. Biol. 57 1733-1743.

� [9] Ong CL, Dahele M, Cuijpers JP, Senan S, Slotman BJ and Verbakel WFAR.

(2013) Dosimetric impact of intrafraction motion during RapidArc stereotactic

vertebral radiation therapy using flattened and flattening filter-free beams. Int J

Radiat Oncol Biol Phys 86(3): 420-5.

� [10] Zhang GG, Ku L, Dilling TJ, Stevens CW, Zhang RR, Li W and Feygelman V.

(2011) Volumetric modulated arc planning for lung stereotactic body radiotherapy

using conventional and unflattened photon beams: a dosimetric comparison with 3D

technique. Radiat Oncol 6:152.

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