Treatment planning for scanned proton beams and IMPT

Transcription

1 Treatment planning for scanned proton SFUD IMPT Tony Lomax, Centre for Proton Radiotherapy, Paul Scherrer Institute, Switzerland

2 Treatment planning for scanning 1. Principles of treatment planning for scanned proton beams 2. Uncertainties and the need for adaptation 3. Where do we go from here?

3 Planning for scanned beams Discrete scanning a treatment planning example Spot selection Spot weight optimisation Optimised dose Dose Calculation Incident field

4 Planning for scanned beams - SFUD A Single Field Uniform Dose (SFUD) plan consists of the addition of one or more individually optimised fields. F3 F4 F1 Combined distribution F2 Note, each individual field is homogenous across the target volume

5 Planning for scanned beams - IMPT An Intensity Modulated Proton Plan (IMPT) consists of the simultaneous optimisation of all Bragg peaks from all incident beams. E.g. F3 F4 F1 Combined distribution F2 Note, each field is highly in-homogenous across the target volume Lomax 1999, PMB 44:

6 Planning for scanned beams - IMPT Example clinical IMPT plans delivered at PSI Skull-base chordoma 3 field IMPT plan to an 8 year old boy 4 fields 3 fields

7 Planning for scanned beams - IMPT There s more than one way to optimise an IMPT plan Two, 5 field IMPT dose distributions A B 3D IMPT DET Corresponding spot weight distributions from field 2

8 Planning for scanned beams - IMPT There s more than one way to optimise an IMPT plan Multiple Criteria Optimisation (MCO) Chen et al 2010, Med. Phys :4945 Pareto surface (David Craft, MGH)

9 Treatment planning for scanning 1. Principles of treatment planning for scanned proton beams 2. Uncertainties and the need for adaptation 3. Where do we go from here?

10 .Uncertainties and the need for adaptation The advantage of protons is that they stop. The disadvantage of protons is that we don t always know where 10% range error

11 Uncertainties and the need for adaptation The Bermuda Triangle of range uncertainties Beam energy [σ] Patient positioning [σ] Inherent CT uncertainties (beam hardening, calibration etc) [Σ] Distal end RBE enhancements [Σ] CT artifacts [Σ] Variations in patient anatomy [Σ,σ] Potential magnitude

12 Uncertainties and the need for adaptation The Bermuda Triangle of range uncertainties Beam energy [σ] Patient positioning [σ] Inherent CT uncertainties (beam hardening, calibration etc) [Σ] Distal end RBE enhancements [Σ] CT artifacts [Σ] Variations in patient anatomy [Σ,σ] Potential magnitude

13 Uncertainties and the need for adaptation Inherent CT uncertainties calibration to proton stopping powers Stoichiometric calibration (PSI) 1 Validation with biological (cow) samples 2 ~1% range uncertainties through soft tissues, ~2% through bone ~1.5mm range uncertainty in brain, ~3.5mm for prostate (lateral beams) 1 Schneider et al 1996, 2 Schaffner and Pedroni1998

14 Uncertainties and the need for adaptation Inherent CT uncertainties effects on dose distributions SFUD IMPT Dose distribution Errormagnitude distribution (+/-3% range) Albertini et al, PMB, 56: , 2009

15 Uncertainties and the need for adaptation Robust IMPT planning the manual approach Lomax et al 2001, Med. Phys. 28:

16 Uncertainties and the need for adaptation Robust IMPT planning the automated approach Field 1 Field 2 Field 3 Optimised fields using robust optimisation Total dose Unkelbach et al, PMB, 52; , 2007

17 Uncertainties and the need for adaptation The Bermuda Triangle of range uncertainties Beam energy [σ] Patient positioning [σ] Inherent CT uncertainties (beam hardening, calibration etc) [Σ] Distal end RBE enhancements [Σ] CT artifacts [Σ] Variations in patient anatomy [Σ,σ] Potential magnitude

18 Uncertainties and the need for adaptation Effects of reconstruction artifacts Titanium implants (stabilisation) Hip prosthesis

19 Uncertainties and the need for adaptation kv-ct Stopping power profiles Effects of reconstruction artifacts single field prostate PTV Stopping power KV SP MV SP X (voxels) MV-CT kv-ct artifacts Prosthesis Albertini et al, PTCOG 2006

20 Uncertainties and the need for adaptation The Bermuda Triangle of range uncertainties Beam energy [σ] Patient positioning [σ] Inherent CT uncertainties (beam hardening, calibration etc) [Σ] Distal end RBE enhancements [Σ] CT artifacts [Σ] Variations in patient anatomy [Σ,σ] Clinical impact

21 Range uncertainties Patient anatomy changes 1. Variations in bowel filling Repeat Planning CT, CT1 st fraction Planning CT Repeat CT Francesca Albertini and Alessandra Bolsi (PSI)

22 Uncertainties and the need for adaptation Patient anatomy changes 2. Changes in patient weight 3 field IMPT to nominal CT Planning CT New CT after 1.5Kg weight gain Up to 1.5cm range changes at distal end of CTV Francesca Albertini and Alessandra Bolsi (PSI)

23 Uncertainties and the need for adaptation Patient anatomy changes 3. Changes in nasal cavity filling Planning CT Repeat CT after 2 weeks

24 Treatment planning for scanning 1. Principles of treatment planning for scanned proton beams 2. Uncertainties and the need for adaptation 3. Where do we go from here?

25 Where do we go from here? Tony s triangle of future developments A personal view In-vivo RBE Accurate dose calculations (E.g. MC) Plan optimisation (Including MCO, robust, 4D etc) Artifact free imaging (Dual-energy CT, MV-CT, Proton CT) Adaptive treatments ( treatment of the day and dose accumulation)

26 and finally the Swiss triangle P + Thanks for your attention