Treatment PlaCancer: Dosimetr

Indrin J ChIndrin J. Ch

Henry Ford Hy

anning of Lung ric Considerations

hetty PhDhetty, PhD

Health Systemy

DiscloDisclo

My department receives r

• NIH/NCI

• Varian Medical Systems• Varian Medical Systems

• Philips HealthCare

osureosure

research support from:

ss

Learning Objeg jTo discuss the physics related to luspecial emphasis on small tumor s

To review dose calculation accuracTo review dose calculation accuraclung planning/dose calculation

To present approaches to improveusing simplistic calculation algorit

To review example volumetric arc h i l itechnical issues

ctives/Outlineung tumor dose coverage, with sizes and location

cy with different algorithms forcy with different algorithms for

e plan quality especially when hms for lung cancer planning

therapy plans and discuss

Pre Test Q

1 For the treatment of small lung tu1. For the treatment of small lung tualgorithm is contra-indicated for S

A. 1-D Pencil Beam B. 3-D Pencil Beam C Superposition/ConvolutionC. Superposition/ConvolutionD. Monte Carlo E. Both A and B

Question

umors located peripherally which dosumors located peripherally, which dosSBRT-based treatment planning:

The Primary Issue: Un

omparison of the 100% IDLs, Pen

nderdosage of the PTV

ncil beam (dashed) and MC (solid

Lateral ScatterM C l i l iMonte Carlo simulati

ring of electrons:10 MV il bon, 10 MV pencil beam

Impact of electron sb fpenumbra: conf

Note the differences in doseNote the differences in dosebroadening

PBPB

scattering on beam f l l lformal lung plane gradient due to penumbrale gradient due to penumbral

MCMC

Loss of Charged PartiCPE exists in a volume if each charCPE exists in a volume if each charvolume is replaced by an identical

broad photon field

volume

In narrow field, CPE is lost and dos

cle Equilibrium (CPE)ged particle (electron) leaving theged particle (electron) leaving the electron entering the volume

narrow photon field

volume

se reduction can be severe

Small field central axis de1.0

0.8

ρ=10.5

ρ=1ρ=0.2 ρ=

0.30 4 8 12

“Build down effect” – severescattering of electrons into tDose builds up in the tumor periphery.

epth dose: slab phantom Ion Chamber

MC (DPM)

6x, 2x2 cm

=1

16 20 24

e dose reduction caused by the lung tissue resulting in underdosage at tumor

Implications for

1.0 Ion Cham

MC (DPM)

0.8

( )

6x, 2x2

0 50.5ρ=1

ρ=0.2 ρ=1

0.30 4 8 12 16 20

Depth (cm)

Ring” of underdosage gets larger

Depth (cm)

Ring of underdosage gets largerpproaches the e’ range) and high

“island” tumors

ρ = 1 0

mber

) ρ = 1.0

“Ring” of

)

cm

ρ = 0.2 ρ = 1

Ring of underdosa”rebuildupof dose

24

r for smaller tumors (as sizer for smaller tumors (as size her energies due to larger e- rang

Pencil Beam

The Energy Effect The Energy Effect

Pencil Beam (6 MV)

95%

90% PTV90% PTV

C-S (6 MV)(6 MV)

95%

90%PTV

Pencil Beam

(low vs. high MV)(low vs. high MV)

(18 MV)

95%

90% PTV90% PTV

C-S (18 MV)

PTV

95%90%

The Energy E

PTV DVHs (PB vs. AAA), 6 PB: mean = 70 2 GyPB: mean = 70.2 GyAAA: mean = 68.9 GyDiff i i PTV dDiff. in min. PTV dose

Effect (6 MV)

AAAPB

MV

11%= 11%

The Energy E

PTV DVHs (PB vs. AAA), 18PB 70 5 GPB: mean = 70.5 GyAAA: mean = 64.7 GyDiff. in min. PTV dose =

Effect (18 MV)

AAAPB

8 MV

= 16%

Accuracy of dose calcuAccuracy of dose calcu

PB80%

PTV80%

95%

PTVITV

ulations for lung SBRTulations for lung SBRT

PTV diam. = 3.2 cm

PTV vol. = 14.6 cc

80%PTV

MCPTV

DVH comparisDVH comparisMC plan recomputed uMC plan recomputed uMC plan recomputed uMC plan recomputed u

58

on for the PTV on for the PTV using MUs from PB planusing MUs from PB planusing MUs from PB planusing MUs from PB plan

MC PB

8% 98%

MC PB

PTV mean dose diff. vs. PTVPTV mean dose diff. vs. PTV

20 40

-5.5

20 40

PTV mean dose diff %dose diff.% MC-PB]

15.5-

25.5-

V diam. (mm): 100 patientsV diam. (mm): 100 patients

PTV diam. (mm)

60 80 10060 80 100

MLD (MC) as a function oMLD (MC) as a function o

10

8

MLD (Gy)6

MLD (Gy) MC

4

2

00 2 40 2 4

MLD (G

of MLD (PB): 50 patientsof MLD (PB): 50 patients

y = 0.9093x - 0.0755R2 0 9948R2 = 0.9948

6 8 10 126 8 10 12Gy) PB

Comparative DoseComparative Dose

Purpose: To investigate dobetween treatment plans

• 1-D Pencil beam (PB) – (il b ( li• 3-D Pencil beam – (Eclip

• Anisotropic Analytic Algp y gconvolution-type, Eclipse)• Pinnacle Collapsed Co• Pinnacle – Collapsed Coconvolution-type, Pinnacl• Monte Carlo (iPlan Brai

e Calculation Study e Calculation Study

osimetric differences computed with:

(iPlan BrainLAB) i )pse, Varian)

gorithm (AAA, g ( ,)ne Convolution (CCCne Convolution (CCC, e, Philips) nLAB)

6X, central tumor: M6X, central tumor: M

100

80

60

40

20

0

20

Dose (Gy)0

20 25 30 35

U for the 1DU for the 1D--PB plan PB plan

AAA

1D-PBMC

3D-PBCCC

40 45 50 55

6X, peripheral 6X, peripheral 100100

80

60

40

20

000 10 20

tumor: 12 Gy x 4tumor: 12 Gy x 4

1D-PBAAAMC

CCC

MC

3D-PB

CCC

30 40 50

% difference in PTV% difference in PTV11 l11 l

% diff 1D PB 3D

11 lung ca11 lung ca

% diff.

Dx-Dmc

1D-PB 3D

Dx Dmc

Ave 29.2 2e 29.2 2

STD D 12 1 1STD Dev 12.1 1

Max Diff. 63.2 4

V min. dose vs. MC, V min. dose vs. MC, ll

D PB AAA CCC

ncer plansncer plans

D-PB AAA CCC

21.6 1.5 -2.021.6 1.5 2.0

12 8 4 6 5 112.8 4.6 5.1

48.5 12.7 8.7

What can be done to

Increase the prescription dose

Increase the PTV margin and hIncrease the PTV margin and hfix the lateral scattering probleincreases unintended dose to hincreases unintended dose to h

Use beams with smallest path i ( h 6X hi henergies (choose 6X over highe

o improve the plan?

– non-uniformity in target

hence the field size – will nothence the field size will not em but will help restore CPE -healthy lung tissuehealthy lung tissue

length through lung and low MV)er MV)

What can be done to

N l b b hNon-coplanar beams may be h– electron lateral scattering is c

ddi l badding more co-planar beams

One size doe

Each case must be judged by lo

o improve the plan?

h l f l d di l tihelpful depending on location cylindrically symmetric;

ill i hwill not improve the coverage

es not fit all!

ocation and field size

VMAT (RapidArcc) Example Case

RapidArc (2 partial arcs) IMRT

DVHs for normal lung g

V20 (RA) = 26.4%; MLDV20 (IMRT) = 27 5%; 14V20 (IMRT) = 27.5%; 14

IMIMIMIM

RARARARA

and R peripheral PTVp p

RARARA

IMRT

RA

IMRT

RA

IMRT

RA

D = 14.2 Gy4 7 Gy4.7 Gy

MRTMRTMRTMRT

VMAT vs. IMRT

Target coverage was somewha

Lungs

MLD (G )

Esophagus

M (G )MLD (Gy) Mean (Gy)

RA 14.7 17.5

IMRT 14.2 20.3

Case: Summary

t better with RA vs. IMRT

Heart

M (G )

Cord

M

MU and (Beam-onMean (Gy) Max

(Gy)

(Beam-onTime)

11.3 35.8 475(0.8 min

8.2 36.5 1563 (2 6 min(2.6 min

VMAT and the IDescribes the interaction betwemotionmotion

From Bortfeld et al Physics in MFrom Bortfeld et al. Physics in M

Interplay effect in IMRT is genefor highly fractionated treatme

Interplay Effecteen organ motion and MLC leaf

Medicine and Biology: 47 2002Medicine and Biology: 47, 2002

erally small (~1%) especially ents

M ti lit d 1 3 i S/

VMAT and the I• Motion amplitude: 1.3 cm in S/• Rapid Arc (RA) plan – two 180 d• Interplay effect incorporated an• Interplay effect incorporated an

both RA and IMRT plans

/I 0 2 i R/L 0 4 i A/P

Interplay Effect/I, 0.2 cm in R/L, 0.4 cm in A/Pdeg. Arcs; IMRT plannd compared to “static case” fornd compared to “static case” for

Tumor Motion: ExhaINH (Axial

INH (Cor)

ale and Inhale StatesEXH (Axial

EXH (Cor)(Co )

DVHS (PTV and normal lung)IMRTIMRT

PTV min. dose diff. =

) with and without interplayT planT plan

with interplay18% with interplaywith interplayp yp ywith interplay

DVHS (PTV and normal lung)R idARapidA

) with and without interplayA lArc plan

with interplay

Overall S

Simulation, planning and deliveconfounded by motion and hetconfounded by motion and het

Lung tissue density impacts tug y psignificantly requiring accurat

umor size is important – pay spwith field sizes close to the elecwith field si es close to the elec

Location! Locat

Convolution/superposition or Mused for lung cancer treatment

Summary

ery of lung cancer is terogeneity in tissue densityterogeneity in tissue density

umor dose deposition pte dose algorithms

pecial attention to small tumoctron rangectron range

tion! Location!

MC-based methods should be t planning

Overall S

High energy photon beams (>

VMAT/R idA ff ffiVMAT/RapidArc offers an efficparticularly in the context of S

Interplay effects tend to be smp yor VMAT, however, further invunderstand these effects in thunderstand these effects in th

Summary

> 6 MV) should be avoided

i t l ti t RT d licient solution to RT delivery, SBRT

mall in the context of IMRT vestigation is needed to fully he VMAT settinghe VMAT setting

AcknowleColleagues

Colleagues at Un

Assistance fr

Colleagues at Un

BrainLab (FeldkirPhilips Radiation OPhilips Radiation O

Varian Medi

NIH/NCI Gra

Dr. Akila Viswanathan (Chair) anCristin Watson and o

dgementsat HFHS

iv of Michigan

rom Industry

iv of Michigan

yrchen, Germany)Oncology SystemsOncology Systemsical Systems

ant Support

d Dr. Ramesh Rengan (Co-Chair)other ASTRO HQ staff

Post Test

1 For the treatment of small lung tu1. For the treatment of small lung tualgorithm is contra-indicated for S

A. 1-D Pencil Beam B. 3-D Pencil Beam C Superposition/ConvolutionC. Superposition/ConvolutionD. Monte Carlo E. Both A and B

Question

umors located peripherally which dosumors located peripherally, which dosSBRT-based treatment planning:

Test Questi

E: Under small field conditions, and lower den,dominant factor influencing dose to the tumor. Peaccount for electron scattering either implicitly inaccurate under such circumstances. Thereforecontext of SBRT planningcontext of SBRT planning. References: S. Benedict, K. Yenice, D. Followil, et al. " Stereo, , ,Task Group 101", Med Phys 37, 4078-4101 (2011

I. Das, G. Ding, A. Ahnesjo, " Small fields: Non206 215 (2008)206-215 (2008).

ion Answer

nsity lung tissue, electron scattering becomes thy g , gencil beam algorithms (1-D or 3-D) do not properor explicitly and have been shown to be quit

e pencil beam algorithms are contra-indicated in th

otactic body radiation therapy: The report of AAPMy py p1).

equilibrium radiation dosimetry", Med Phys 35 (1