Post on 26-May-2015
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
diapositiva 3G.Guidi, E.Cenacchi, et.al.
+
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?
diapositiva 4G.Guidi, E.Cenacchi, et.al.
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
diapositiva 5G.Guidi, E.Cenacchi, et.al.
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
diapositiva 6G.Guidi, E.Cenacchi, et.al.
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
diapositiva 7G.Guidi, E.Cenacchi, et.al.
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
diapositiva 8G.Guidi, E.Cenacchi, et.al.
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
diapositiva 9G.Guidi, E.Cenacchi, et.al.
DOWNSAMPLE IMAGE AND DOSE MATRIX EFFECT ON CORD
512x512
256x256CORD
55Gy
CORD Details
Cumulative DVH
Volume effect
CORD
53Gy
diapositiva 10G.Guidi, E.Cenacchi, et.al.
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?
diapositiva 11G.Guidi, E.Cenacchi, et.al.
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
diapositiva 12G.Guidi, E.Cenacchi, et.al.
GAMMA 2D ANALYSIS - PTV HIGHEST PRIORITY vs. CORD (DOSE MATRIX: 256X256 VS. 512X512)
DTA 5 DTA 3
DTA 2 DTA 1
diapositiva 13G.Guidi, E.Cenacchi, et.al.
GAMMA 2D ANALYSIS - CORD HIGHEST PRIORITY vs. PTV(DOSE MATRIX: 256X256 VS. 512X512)
DTA 5 DTA 3
DTA 2 DTA 1
diapositiva 14G.Guidi, E.Cenacchi, et.al.
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
diapositiva 15G.Guidi, E.Cenacchi, et.al.
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
Guidi.Gabriele@policlinico.mo.it
Tel. +059 422 5699 – ext. 4270“... where we are going.....”