elekta 2017 australasian user meeting 12th november 2017, …d2fa2cad-3302-4fd6-80c5... ·...

Elekta 2017 Australasian User Meeting12th November 2017, Newcastle, NSW

This work aims to compare ITVs defined using 4DCBCT data in two treatment planning systems (TPS) and to assess their impact on planned dose


Background: Lung SABR in NT

Introduction: ITV in lung SABR

Method: ITV definition using 4DCBCT

Validation: Validation of 2 methods

Results: Volume Analysis + Plan Evaluation

Discussion: Uncertainty + Adv./Disadv.

Conclusion: Major findings + implications


Only RT centre in NT

Low population ◦ 30-40 patients per day

High Indigenous population◦ High incidence lung cancer

◦ Advanced presentations

◦ High COPD


Alan Walker Cancer Care Centre - AWCCC

CT

•Toshiba Wide Bore

•No 4DCT

TPS•Pinnacle

Linac

• 2 Elekta Synergy

• MLCi2

• 4D CBCT XVI Symmetry

SABR for lung only

First patient treated October 2016

Total 16 patients treated to date

3DCRT + non-coplanar beams

48Gy / 4 Fx

Dose escalation planned for 2018


SABR for lung cancer relies on accurate definition of tumour motion using an internal target volume (ITV).

Typically 4DCT is utilised to define the ITV

Two methods of ITV definition using 4-dimensional cone-beam CT (4DCBCT) data are described.


Manual Method - Pinnacle

MIP Method - Monaco

End-to-end testing

Localisation of moving target

Tumour remains within ITV

Moving/static dose

<1% difference


Patient Ratio

1 0.904

2 0.986

3 0.750

4 0.577

5 0.869

6 0.466

7 0.364

8 0.491

9 0.509

10 0.447

11 0.734

12 0.544

13 0.820

14 0.810

15 0.7840

5

10

15

20

25

30

35

40

45

50

55

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

ITV

Volu

me (cm

3)

Patient

ITV Manual

ITV MIP


All ITVs reduced

0

10

20

30

40

50

60

70

80

90

100

110

120

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

PT

V V

olu

me (cm

3)

Patient

PTV Manual

PTV MIP

Patient Ratio

1 1.023

2 1.086

3 0.886

4 0.873

5 0.920

6 0.724

7 0.604

8 0.843

9 0.754

10 0.620

11 0.760

12 0.726

13 0.931

14 0.907

15 0.981


9/15 > 10% difference

Replans in Pinnacle

Isocentre

Beam angles

Target coverage maintained

2 patients excluded - PTV coverage could not be met



0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 7 8 9 11 12 13 14 15

Num

ber

OA

R C

onstr

ain

ts

Patient

Decreased

Increased

Unchanged

All 13 patients experienced dose reduction for one or more OAR constraints◦ Average 75% OAR doses decreased by replan

6/13 patients had one or more OAR reduced ≥10%

Most clinically insignificant

3 cases reviewed


0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Volu

me (%

)

Patient

Lungs - GTV: V20 <10%

ITV Manual

ITV MIP


Patient 11 Constraint Planning Aim ITV Manual ITV MIP

CI 100 % ≤1.2 / ≤1.2 1.03 1.08

CI 50 % <3.35 / <3.47 3.27 3.54

LUNGS -GTVV20 <10 10.69 9.72

Mean (Gy) <20 7.0 6.55

SPINAL CANAL

Point max (Gy) <26 6.5 6.45

0.35cc Vol. max (<20.8Gy) 5.4 5.8

1.2cc Vol. max (<13.6Gy) 4.6 4.3

HEARTPoint max (Gy) <34 18.62 17.88

15cc Vol. max (<28Gy) 13.7 13.4

GREAT VESSELSPoint max (Gy) <49 16.76 14.76

10cc Vol. max (<43Gy) 9.1 8.5

OESOPHAGUSPoint max (Gy) <30 9.15 9.04

5cc Vol. max (<18.8Gy) 7.7 7.4

SKINPoint max (Gy) <36 19.17 18.55

10cc Vol. max (<33.2Gy) 13.8 13.5

TRACHEA & LARGE BRONCHUS

Point max (Gy) <34.8 17.15 15.3

4cc Vol. max (<15.6Gy) 0.9 0.8

CHEST WALL/RIBSPoint max (Gy) <40 47.18 45.4

1cc Vol. max (<32Gy) 37.7 37

NORMAL TISSUE %<68.97 / <66.66

66.78 63.96

Patient 11

48Gy/4Fx

PTV Manual97.507cm3

PTV MIP74.115cm3



CI 100 % ≤1.2 / ≤1.2 1.07 1.03

CI 50 % <3.67 / <3.80 4.02 3.88

LUNGS -GTVV20 <10 16.29 14.29

Mean (Gy) <20 10.14 9.19

SPINAL CANAL

Point max (Gy) <26 13.38 17.5

0.25cc Vol. max (<22.5Gy) 11.8 13.4

0.5cc Vol. max (<13.5Gy) 11.6 12.5


15cc Vol. max (<28Gy) 16 15.7


10cc Vol. max (<47Gy) 8.7 6.7


5cc Vol. max (<27.5Gy) 9.5 7.7


10cc Vol. max (<30Gy) 15.9 15.6


Point max (Gy) <63 32.59 17.53

4cc Vol. max (<18Gy) 1.6 1.15

CHEST WALL/RIBSPoint max (Gy) <40 40 39.82

1cc Vol. max (<32Gy) 32.5 32.35

NORMAL TISSUE %<64.62 / <63.61

70.2 69.84

Patient 5

60Gy/8Fx

PTV Manual63.1022cm3

PTV MIP58.074cm3



CI 100 % ≤1.2 / ≤1.2 1.03 1.05

CI 50 % <4.97 / <5.05 5.86 5.96

LUNGS -GTVV20 <10 1.03 0.92

Mean (Gy) <20 1.52 1.4

SPINAL CANAL

Point max (Gy) <26 6.85 6.83

0.35cc Vol. max (<20.8Gy) 6.6 6.5

1.2cc Vol. max (<13.6Gy) 6.4 6.3


15cc Vol. max (<28Gy) 0.4 0.3


10cc Vol. max (<43Gy) 6.8 4.3


5cc Vol. max (<18.8Gy) 0.5 0.4


10cc Vol. max (<33.2Gy) 9.6 9.3


Point max (Gy) <34.8 6.41 6.02

4cc Vol. max (<15.6Gy) 3.9 3.3

CHEST WALL/RIBSPoint max (Gy) <40 59.27 59.33

1cc Vol. max (<32Gy) 41.6 41

NORMAL TISSUE % <50 / <50 54.06 49.45

PTV Manual9.34cm3

PTV MIP8.15cm3

48Gy/4Fx

Patient 4


Contouring – assessed through team meeting

Motion artefacts in CT and CBCT

Different position/breathing pattern from CT to CBCT

Fusion


Disadvantages

Poor Image quality

Additional fusion

Additional machine time

Dose calculation on free breathing

Increased QA


Advantages

No 4DCT required

Tumour motion captured in treatment position

Adequate tumour coverage

Tumour motion verified at treatment


Manual MIP

Image quality XTarget coverage X

OAR doses XTime X

Accuracy

ITV definition using Symmetry validated for Lung SABR ◦ Manual + MIP◦ Pinnacle + Monaco

MIP method produces smaller volumes more indicative of true tumour motion most of the time◦ Exceptions – lateral or inferior located tumours

Manual method more likely to over-contour

MIP ITVs resulting in smaller PTVs reduced OAR dose in all cases although reduced target coverage in some cases

Although majority of OAR doses were subsequently reduced, clinically significant plan changes were rare and therefore overall plan acceptability was comparable


Jeremy Plawecki, Senior RT – planning

Dr. Thanuja Thachil, RO – contouring

Elekta – Monaco education station


elekta 2017 australasian user meeting 12th november 2017, …d2fa2cad-3302-4fd6-80c5... ·...

Documents