Treatment Planning (Protons vs. Photons)

Transcription

1 Treatment Planning Treatment Planning (Protons vs. Photons) Acquisition of imaging data Delineation of regions of interest Selection of beam directions Dose calculation Optimization of the plan Hounsfield Units (HU)? HU Photon Planning System HU versus electron density Proton Planning System HU versus rel. stopping power 7/28/ /28/ Treatment Planning (Protons vs. Photons) Proton beams (fields) have an end of range (i.e. pointing to critical structures is an option) Treatment Planning (Protons vs. Photons) Isodose levels The PTV concept is not applicable in proton therapy Planned to the PTV Dose versus time 7/28/ Martijn Engelsman, MGH 7/28/

2 Treatment Planning Dose shaping for passive scattered protons Passive scattered proton beams Scanned proton beams Intensity modulated proton beams Comparative treatment plans Beam High-Density Structure Target Volume Critical Structure Double scattering system Aperture Body Surface 7/28/ Hanne Kooy, MGH 7/28/ SOBP Modulation Aperture and Range Compensator High-Density Structure Target Volume + = Beam Critical Structure Aperture Body Surface Prescription: Range Modulation Compensator Aperture 7/28/2008 Hanne Kooy, MGH 7 To be designed by the planning system! 7/28/2008 Hanne Kooy, MGH 8 2

3 Dosimetry and QA for SOBP proton fields Range and Modulation Width for each field Dose [%] Dose [%] Dose [%] 40 Beam range: cm 20 Modulation width: 6.78 cm Depth [mm] Depth [mm] 7/28/ Beam range: cm 20 Modulation width: 8.65 cm Depth [mm] Beam range: 12.0 cm Modulation width: 4.0 cm Volume for absolute dosimetry Output Factor D cal cgy MU 7/28/ i ic 2. Absolute dosimetry for each field A SIMPLE EXAMPLE: Para-spinal case using 3 fields Field Patching 10 Gy 15 Gy 20 Gy 25 Gy 30 Gy 35 Gy 40 Gy 45 Gy 46 Gy brainstem CTV B PTV Critical Structure C A Useful if target is close to critical structures Not necessarily homogeneous dose to the target for each beam (IM!) Range and penumbra uncertainties need to be considered 7/28/ /28/

4 A COMPLICATED EXAMPLE: Nasopharynx case using 14 fields (plus additional photon fields to the lower neck) CTV-2 25 Gy 30 Gy 35 Gy 40 Gy 45 Gy 50 Gy 55 Gy 60 Gy 67 Gy 7/28/ /28/ Marc Bussiere, MGH CTV-2 Parotid Brainstem CTV-1 Treating moving targets with protons Spinal Cord GTV 76 Gy CTV Gy CTV2 60 Gy 7/28/ Nodes 54 Gy 7/28/

5 Effect of respiration on dose FH Burr Proton Therapy Center (2001-) Patient Population Brain 32% Rescanning Spine 23% Beam Gating Real time tumor tracking with markers Prostate 12% Skull Base 12% Head & Neck 7% Trunk/Extremity Sarcomas R L 6% posterior view Gastrointestinal 6% posterior cut Lung 1% In general, 1-3 fields / day / patient Currently ~ 45 patients / day 7/28/2008 Eike Rietzel 17 Shinishiro Mori, MGH 7/28/ Thomas DeLaney, MGH Treatment Planning Beam Scanning Passive scattered proton beams Scanned proton beams Intensity modulated proton beams Comparative treatment plans Intensity Modulated Beam Pair of Quads Scanning Magnets Fast Slow Vacuum Chamber Beam monitor 0.8 m 0.6 m Y Z X 7/28/ No double scattering system No modulator wheels No aperture No range compensator 7/28/

6 Beam Scanning 1 1. Evenly spaced/weighted spots to achieve uniform field 2. 1mm spot error due to delivery error or patient motion. Typical Spot Beam in Water 3. Optimum spacing/weighting to achieve sharper penumbra 2 3 Eros Pedroni, PSI 7/28/ Pedroni Eros Pedroni, PSI 7/28/ Dosimetry and QA of pencil beams Energy/Range large number of energies required energy spacing must provide dose uniformity over all depths Spot size and shape spot size/shape may depend on energy spot position accuracy Measurements require methods for rapid collection large amounts of data Real-time beam information Ionization Chamber Array Water column with 26 small ionization chambers of 0.1 cm 3 Dose box PTCOG 46 Educational Workshop Pedroni, PSI, Switzerland Pedroni, PSI, Switzerland Orthogonal IC array measurements performed at different water depthsusing acomputercontrolledwatercolumnand compared with calculations. Beam s-eye-view of dose in water U axis profile Mirror M D Anderson Cancer Center CCD Scintillating Plate, Mirror and Camera CCD Camera used for pencil beam scanning QA. Scintillating Plate Beam Spot Pattern Test Uniform Field Scanning Test Scintillating screen viewed with a ideal for non homogeneous dose distributions CCD through a 45 mirror WER W= 6.65 cm 6.65 CM WE W= 7.82 cm R 7.82 CM 7/28/ Alfred Smith, MDACC T axis profile Measurement vs. Calculation 7/28/ PTCOG 46 Educational Workshop Pedroni, PSI, Switzerland Alfred Smith, MDACC 6

7 Treatment Planning Passive scattered proton beams Scanned proton beams Intensity modulated proton beams Comparative treatment plans IMPT Treatment Planning Bragg peaks of pencil beams are distributed throughout the planning volume Pencil beam weights are optimized for several beam directions simultaneously (inverse planning) 7/28/ Alex Trofimov, MGH 7/28/ Intensity-Modulated Proton Therapy IMPT Treatment Planning Passive scattered proton beams Scanned proton beams Intensity modulated proton beams Comparative treatment plans 7/28/ Alex Trofimov, MGH 7/28/

8 Example (passive scattered protons vs. photons) Protons Medulloblastoma Photons Medulloblastoma 7/28/ /28/2008 Copyright MGH/NPTC Example (protons vs. IM photons) Prostate carcinoma: (GTV + 5mm) to 79.2 Gy (CTV + 5mm) to 50.4 Gy (a) IMRT Prostate (b) Pass. Sc. Protons (c) Dose [Gy] IMPT Dose [CGE] Dose [CGE] 7/28/ Alex Trofimov, MGH 7/28/

9 Example (protons / IM protons / IM photons) Nasopharynx (case shown earlier) 7/28/ /28/ Alex Trofimov, MGH A Passive scattered protons (14 proton fields, 4 photon fields) proton fields CTV to 59.4 GyE (33 x 1.8 Gy) GTV to 70.2 GyE (+ 6 x 1.8 Gy) Photon fields lower neck, nodes to 60 Gy B Photon IMRT plan (7 coplanar photon beams) G N N G 7/28/ /28/ Alex Trofimov, MGH Alex Trofimov, MGH 9

10 C IMPT plan (4 coplanar proton beams) DVH for target structures Comparable target coverage 7/28/ /28/ Alex Trofimov, MGH Alex Trofimov, MGH DVH for some critical structures Summary 7/28/ Proton planning offers more options in terms of beam directions and field shaping than photon planning IMRT and 3D protons can be comparable in terms of dose conformality Protons are able to reduce the dose to most critical structures compared to photons Proton therapy is able to reduce the integral dose compared to photons by up to a factor of 3 IMPT is the method of choice Alex Trofimov, MGH 7/28/

11 Some remarks on biology Integral dose (protons vs. photons) Neutrons in proton therapy The proton RBE 7/28/ Advantage protons!!! Dis-advantage protons??? 7/28/ Neutron dose as a function of lateral distance Field 1 Zacharatou Jarlskog and Paganetti: 7/28/2008 Zacharatou Jarlskog and Paganetti: Int. J. Radiat. Biol. Phys. 2008, in press 43 7/28/2008 Field 2 Field 3 Int. J. Radiat. Biol. Phys. 2008, in press 44 11

12 Neutron radiation weighting factor Neutron RBE as a function of endpoint Estimates of RBE M for neutron carcinogenesis in mice From: Annals of the ICRP; ICRP Publication 92; Relative Biological Effectiveness (RBE), Quality Factor (Q), and Radiation Weighting Factor (w R ) 7/28/ NCRP Report No. 104, The Relative Biological Effectiveness of Radiations of Different Quality 7/28/ RBE in proton therapy: RBE values in vivo (center of SOBP; relative to 60 Co) 2.5 Clinical (generic) RBE = 1.1* RBE * Based on experiments at the Harvard cyclotron done in the 70 s 7/28/ Dose per fraction [Gy] Mice data: Lung tolerance,crypt regeneration,acute skin reactions,fibrosarcoma NFSa Paganetti et al.: Int. J. Radiat. Oncol. Biol. Phys. 2002; 53, /28/

13 RBE as a function of LET be careful when using the end of range next to a critical structure RBE as a function of dose dose dependency seems to be small RBE as a function of biological endpoint variation seems to be small Note: RBE for cell kill can be different than for mutation/carcinogenesis 7/28/ RBE as a function of particle energy / LET Radiation is more effective when energy depositions are more concentrated in space p+ 7/28/ M. Krämer, W. K. Weyrather, M. Scholz: Techn. Cancer Res. Treatm. 2, , 2003 Thanks to Hanne Kooy Alex Trofimov George Chen Martijn Engelsman Judy Adams for providing some slides and figures 7/28/