TRAJECTORY- BASED TREATMENT PLANNING AND DELIVERY FOR CRANIAL RADIOSURGERY

Transcription

1 TRAJECTORY- BASED TREATMENT PLANNING AND DELIVERY FOR CRANIAL RADIOSURGERY JAMES ROBAR, PHD, FCCPM LEE MACDONALD, MSC CHRISTOPHER THOMAS, PHD, MCCPM DALHOUSIE UNIVERSITY, CANADA

2 CLASS SOLUTIONS IN SRS/SRT Identical arc arrangement at cardinal angles for all cases No patient-specific customization to the arc arrangement Cranial cases are highly variable with regard to PTV and OAR geometry

3 PATIENT-SPECIFIC ARC TRAJECTORY Establish patienttailored dynamic arc trajectories May involve coordinated gantry and couch motion Designed to minimize dose to OARs without compromising PTV coverage

4 TRAJECTORY BASED PLANNING ALGORITHM CONSIDERATIONS

5 FOUR CONSIDERATIONS Overlap between PTV and OAR Algorithm Objectives Relative Depth OAR PTV PTV OAR QUANTEC Dose Weighting Promote Rapid Dose Fall-off

6 Area (mm 2 ) Area (mm 2 ) OAR OVERLAP in FOUR-PI Geometric optimization Area of VOI vs. Gantry Angle 2500 PTV Brainstem PTV Brainstem Gantry Angle (Deg) Overlap 3000 Area of Overlap vs. Gantry Angle Gantry Angle (Deg)

7 Relative Cost OAR OVERLAP in FOUR-PI Creates a suitability ranking for every couch-gantry position EXAMPLE: brainstem map Unique map for every patient Condenses three dimensional relationships between structures Higher penalty assigned with OAR in front of PTV

8 Relative Cost OAR OVERLAP in FOUR-PI A composite OAR map All OARs Brainstem Chiasm Lenses Eyes Right Optic Nerve Left Optic Nerve

9 20 CRANIAL RADIOSURGERY PATIENTS SAMPLE OVERLAP MAPS

10 TRAJECTORY BASED PLANNING NAVIGATING THE MAP

11 Relative Cost NAVIGATION OF THE MAP Overlay treatment arcs to visualize their exposure to OARs. Measure the amount of cost present in an arc, and remodel the treatment. COLLISION COLLISION Establish safe collision zones.

12 Relative Cost NAVIGATION OF THE MAP Patient Example Right Acoustic Neuroma. Brainstem Eyes Lenses Optic Chiasm Optic Nerves

13 Relative Cost NAVIGATION OF THE MAP Conventional Class Solution Standard cranial template COLLISION COLLISION

14 Relative Cost NAVIGATION OF THE MAP Fixed-Couch Optimization COLLISION COLLISION

15 Relative Cost DYNAMIC TRAJECTORY COLLISION COLLISION

16 Relative Cost DYNAMIC TRAJECTORY COLLISION COLLISION

17 TRAJECTORY BASED PLANNING EXAMPLES AND RESULTS

18 DOSE REDUCTION ~ 20% (N=30) RL Macdonald, C Thomas, Dynamic trajectory-based couch motion for improvement of radiation therapy trajectories in cranial SRT, 42, 2317 (2015)

19 MINIMIZING MODULATION RL Macdonald, C Thomas, Dynamic trajectory-based couch motion for improvement of radiation therapy trajectories in cranial SRT, 42, 2317 (2015)

20 Urgent sparing Relative Cost URGENT SPARING Rewarding dose fall-off toward specific OAR α

21 URGENT SPARING Dose fall-off toward specific OARs % improvement of mean dose, 16 acoustic neuroma patients

22 TRAJECTORY BASED PLANNING DELIVERY

23 DELIVERY (SPEED 8X)

24 NEXT STEPS For FourPi

25 Collimation Example BAD GOOD

26 Dynamic Collimator Arc Arc 1 Arc 2 Arc 3 Arc 4

27 4Pi with Dynamic Collimation

28 BRAINLAB IMPLEMENTATION

29 USER TEMPLATE FourPi in BRAINLAB CRANIAL SRS ELEMENT FIND ALL POSSIBLE ARCS PTV/OAR overlap OAR radiological depth OAR on source side Gantry stop/start deviations Table deviations ASSIGN PENALTIES FIND BEST POSSIBLE SET

30 SUMMARY Approach minimizes overlap of PTV and OARs in dynamic trajectories Multiple OARs accounted for in determining trajectory, each can be individually weighted Can reward regions of approach which allow most rapid fall-off toward a specific OAR Can be applied to optimization of fixed-couch arcs or simultaneous gantry / couch trajectories

31 THANK YOU!

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