Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy

DVH PITFAL IN VOLUME EVALUETION FOR SPINAL CORD USING TOMOTHERAPY PLANNING

G.Guidi, E.Cenacchi, C.Danielli, T.CostiFisica Sanitaria

Azienda Ospedaliero - Universitaria di Modena - Policlinico

diapositiva 2G.Guidi, E.Cenacchi, et.al.

STRUCTURES OVERLAP PRIORITY

1

2

5

3

4

1

2

5

4

3

2

1

5

3

4

3

2

5

4

1

ROI=2,3 NOT CALCULABLE -> NO PLAN OPTIMIZATIONROI=3,4 HAVE DIFFERENT OVERLAP PRIORITY -> DIFFERENT DOSE/VOLUME ON DVH


+

CLUSTER RESOLUTION

512x512

CORD54Gy

45Gy

Cord

CLUSTER RESOLUTION

256x256

CORD

54Gy

45Gy

Cord

PATIENT ANOMALY ........ CLUSTER RESOLUTION AND OVERLAP PRIORITY EFFECTS

+

???

???

WHY DVH AND DOSE POINTER HAVE DIFFERENT DOSES?


CORD PITFALL ...USING DIFFERENT STRUCTURES OVERLAP PRIORITY AND DOSE MATRIX....

CORD WITH LOWEST OVERLAP PRIORITY (=3)

(PTV Priority)

CORD WITH HIGHEST OVERLAP PRIORITY (=1)

(CORD Priority)

IMAGE DOWNSAMPLE EFFECT

(256x256 vs. 512x512)

WONDERFUL DVH ...

... DOESN'T MEAN ...

... WONDERFUL DOSE DISTRIBUTION.

CORD AS A TUMOR AND NOT AS A SENSITIVE STRUCTURE IS A TRICK FOR THE TOMOTHERAPY PLAN TO SEE THE REAL VOLUME OF THE CORD

AND USE THE EXPANDED CORD AS PLAN CONSTRAINS


IMAGE DONWSAMPLE EFFECT (CHEESE PHANTOM)(256x256 vs. 512x512)

TARGET=1

(12Gy)TARGET=2

(10Gy)

OAR=3

(8Gy)

OAR=4

(6Gy)

OAR=5

(4Gy)

1

2

5

3

4

256x256

512x512

1

2

5

3

4

256x256

512x512

256x256

512x512

•Same Plan

•Same Objectives

•Same Constrain

•Same Prescription

•Same Iterations

DIFFERENT RESULTS

PTV

OARs

OARs


IMAGE AND DOSE MATRIX EFFECT ON DVH (1)

25cc (512x512)

512x512

20cc (256x256)

256x256 1

4

5

32

256x256

512x512

1

4

5

32

SIMILAR RESULTS

FOR PTV STRUCTURES

OR LARGE VOLUME

DIFFERENT RESULTS

FOR OAR STRUCTURES

OR SMALL VOLUME


IMAGE AND DOSE MATRIX EFFECT ON DVH (2)

4.3Gy (256x256)1

4

5

3

2

256x256

200cc (512X512)

250cc (256X256)

4.0 Gy (256x256)

DEPEND FROM THE VOLUME

SIZE

DONWSAMPLE IMAGE EFFECT


PATIENT STRUCTURE PRIORITY AND DOSE MATRIX COMPARISON(256X256 VS. 512X512)

DIFFERENT STRUCTURES PRIORITIES, SAME IMAGE MATRIX

•CHANGE THE OPTIMIZATION

•DIFFERENT PREFERENTIAL BEAM-ON ANGLES

SAME STRUCTURE PRIORITY, DIFFERENT IMAGE MATRIX:

•VERY SIMILAR OPTIMIZATION WITHOUT ANY CHANGE TO THE CONSTRAIN PENALTY

DOSE MATRIX EFFECT (256X256 VS. 512X512)

•DIFFERENT DOSE (VOXEL VOLUME EFFECT ???)

3Gy DIFFERENCE

PREFERENTIAL BEAM ANGLES

IF THE PTV HAS THE HIGHEST PRIORITY

PREFERENTIAL BEAM ANGLES

IF CORD HAS THE HIGHEST PRIORITY


DOWNSAMPLE IMAGE AND DOSE MATRIX EFFECT ON CORD

512x512

256x256CORD

55Gy

CORD Details

Cumulative DVH

Volume effect

CORD

53Gy


DOWNSAMPLE IMAGE AND DOSE MATRIX EFFECT ON PTV

CUMULATIVE DVH 512x512

256x256

DETAILS

CUMULATIVE DVH

Prescription @95% of the PTV54

(The prescription is a must for the Tomotherapy Plan)

•VERY SIMILAR

•SMALL DIFFERENCE

THE VOLUME EFFECT MAY HIDE SOME DIFFERENCES?

THE DOSE MATRIX?

THE IMAGE DOWNSAMPLE?


OPTIMIZATION COST FUNCTION EFFECT ON BIG VOLUME (E.G. LUNG)

LUNG

256X256

MATRIX EFFECT

(LUNG VOLUME)

LUNG

512X512

LUNG

(CORD THE HIGHEST PRIORITY)

STRUCTURES OVERLAP

PRIORITY EFFECT

(LUNG VOLUME)

LUNG

(PTV THE HIGHEST PRIORITY)

1. Same as the PTV, it seems appreciable small effect based on the images and dose matrix

2. If the volume has a big size in term of cm3 (e.g. lung), small differences may not be reported

3. For big volume the different overlap priority of the “targets structures” does not change to much the objective of the optimization cost function

4. It seems less evident the dominance of the volume on the cost function during the optimization


GAMMA 2D ANALYSIS - PTV HIGHEST PRIORITY vs. CORD (DOSE MATRIX: 256X256 VS. 512X512)

DTA 5 DTA 3

DTA 2 DTA 1


GAMMA 2D ANALYSIS - CORD HIGHEST PRIORITY vs. PTV(DOSE MATRIX: 256X256 VS. 512X512)

DTA 5 DTA 3

DTA 2 DTA 1


EXTRA CASES WITH SIMILAR PROBLEMS ...(WHAT DO I HAVE TO DO? WHICH PRIORITY? DO I HAVE TO USE ANY DUMMY?)

OVERLAP?

PROSTHESIS

ARTIFACTS?

BELIEVE OR

NOT BELIEVE


CONCLUSION

• The new version (4.x) should resolve many of this problems

• The possibility with Tomotherapy are multiple to obtain same results

• The dose performance of the Tomotherapy are very exciting (Dose Painting)

• Physicist must evaluate carefully the structure overlap priority, dose grid and image thickness

• The use of multiple dummies should be limited, to reduce possible misunderstandings on DVH

• The cluster should be switched to 512x512 especially for radiosurgery, but the time calculation must be improved (e.g. Blade cluster solution or 32 nodes)

• The dose grid (e.g. Fine) should be used for most of the plans, wherein small structures or critical organs (e.g. Cord, Brainstem) are close to the gradient area

• Multiple regions inside the PTV (e.g. PET overboost or differential dose boost area) should be weigh up; appreciable effect in the volume DVH may not be appropriate considerations radiobiological expectations (e.g. EUD, NTCP & TCP)

• The DVH’S results are not a must to define the best the plans; dose pointer and isodoses should be carefully assess by the doctors

• Complex plan (e.g. Prosthesis) close to the cord must be carefully evaluated to define the best dose grid and image thickness acquisition

• The downsample of the images (256x256) seems not to influence, but could open some issues

• OARs (e.g. Lens) could be incorrectly calculated without adequate dose grid or cluster resolution

• Margin expansion should be comparable with the dose grid (e.g. 1-2 mm of margin could be not adequate)

• DVH WITH “STAIRS SHAPE” SHOULD AROUSE SUSPICION, IN CASE OF SERIAL ORGANS AND WHERE THE DOSE/VOLUME CONSTRAINS COULD GENERATE UNEXPECTED TOXICITY

DVH PITFAL IN VOLUME EVALUETION FOR SPINAL CORD USING TOMOTHERAPY PLANNING

G.Guidi, E.Cenacchi, C.Danielli, T.CostiFisica Sanitaria

Azienda Ospedaliero - Universitaria di Modena - Policlinico

Guidi Gabriele

Medical Physicist

Az.Ospedaliero-Universitaria di Modena

[email protected]

Tel. +059 422 5699 – ext. 4270“... where we are going.....”

mailto:[email protected]

Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy

Health & Medicine

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