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Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy
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Dvh Pitfal In Volume Evaluetion For Spinal Cord Using Tomotherapy

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  • 1. DVH PITFAL IN VOLUME EVALUETION FOR SPINAL CORD USING TOMOTHERAPY PLANNING G.Guidi, E.Cenacchi, C.Danielli, T.Costi Fisica Sanitaria Azienda Ospedaliero - Universitaria di Modena - Policlinico
  • 2. 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 OPTIMIZATION ROI=3,4 HAVE DIFFERENT OVERLAP PRIORITY -> DIFFERENT DOSE/VOLUME ON DVH
  • 3. PATIENT ANOMALY ..... ... CLUSTER RESOLUTION AND OVERLAP PRIORITY EFFECTS + WHY DVH AND DOSE POINTER HAVE DIFFERENT DOSES? + CLUSTER RESOLUTION 512x512 CORD 54Gy 45Gy Cord CLUSTER RESOLUTION 256x256 CORD 54Gy 45Gy Cord ??? ???
  • 4. 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
  • 5. IMAGE DONWSAMPLE EFFECT (CHEESE PHANTOM) (256x256 vs. 512x512) TARGET=1 (12Gy) TARGET=2 (10Gy) OAR=3 (8Gy) OAR=4 (6Gy) OAR=5 (4Gy) 256x256 512x512 256x256 512x512
    • Same Plan
    • Same Objectives
    • Same Constrain
    • Same Prescription
    • Same Iterations
    • DIFFERENT RESULTS
    PTV OARs OARs 1 2 5 3 4 256x256 512x512 1 2 5 3 4
  • 6. IMAGE AND DOSE MATRIX EFFECT ON DVH (1) 25cc (512x512) 512x512 20cc (256x256) 256x256 SIMILAR RESULTS FOR PTV STRUCTURES OR LARGE VOLUME DIFFERENT RESULTS FOR OAR STRUCTURES OR SMALL VOLUME 1 4 5 3 2 256x256 512x512 1 4 5 3 2
  • 7. IMAGE AND DOSE MATRIX EFFECT ON DVH (2) 4.3Gy (256x256) 200cc (512X512) 250cc (256X256) 4.0 Gy (256x256) DEPEND FROM THE VOLUME SIZE DONWSAMPLE IMAGE EFFECT 1 4 5 3 2 256x256
  • 8. 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
  • 9. DOWNSAMPLE IMAGE AND DOSE MATRIX EFFECT ON CORD 512x512 256x256 CORD 55Gy CORD Details Cumulative DVH Volume effect CORD 53Gy
  • 10. 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?
  • 11. 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)
    • Same as the PTV, it seems appreciable small effect based on the images and dose matrix
    • If the volume has a big size in term of cm 3 (e.g. lung), small differences may not be reported
    • For big volume the different overlap priority of the “targets structures” does not change to much the objective of the optimization cost function
    • It seems less evident the dominance of the volume on the cost function during the optimization
  • 12. GAMMA 2D ANALYSIS - PTV HIGHEST PRIORITY vs. CORD (DOSE MATRIX: 256X256 VS. 512X512) DTA 5 DTA 3 DTA 2 DTA 1
  • 13. GAMMA 2D ANALYSIS - CORD HIGHEST PRIORITY vs. PTV (DOSE MATRIX: 256X256 VS. 512X512) DTA 5 DTA 3 DTA 2 DTA 1
  • 14. 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
  • 15. 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
  • 16. DVH PITFAL IN VOLUME EVALUETION FOR SPINAL CORD USING TOMOTHERAPY PLANNING G.Guidi, E.Cenacchi, C.Danielli, T.Costi Fisica Sanitaria Azienda Ospedaliero - Universitaria di Modena - Policlinico Guidi Gabriele Medical Physicist Az.Ospedaliero-Universitaria di Modena [email_address] Tel. +059 422 5699 – ext. 4270 Grazie “ ... where we are going.....”