Treatment Planning (Protons vs. Photons)

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)? 0 500 1000 1500 2000 2500 3000 HU Photon Planning System HU versus electron density Proton Planning System HU versus rel. stopping power 7/28/2008 1 7/28/2008 2 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 20 50 80 95 100 The PTV concept is not applicable in proton therapy Planned to the PTV Dose versus time 7/28/2008 3 Martijn Engelsman, MGH 7/28/2008 4 1

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 7/28/2008 5 Hanne Kooy, MGH 7/28/2008 6 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

Dosimetry and QA for SOBP proton fields 120 1. Range and Modulation Width for each field Dose [%] Dose [%] Dose [%] 40 Beam range: 17.19 cm 20 Modulation width: 6.78 cm 0 0 50 100 150 200 Depth [mm] Depth [mm] 7/28/2008 9 100 80 60 120 100 80 60 40 Beam range: 13.47 cm 20 Modulation width: 8.65 cm 0 0 20 40 60 80 100 120 140 160 Depth [mm] 120 100 80 60 40 20 0 Beam range: 12.0 cm Modulation width: 4.0 cm 0 20 40 60 80 100 120 140 Volume for absolute dosimetry Output Factor D cal cgy MU 7/28/2008 10 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 50 50 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 7/28/2008 11 7/28/2008 12 3

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 7/28/2008 13 7/28/2008 14 Marc Bussiere, MGH CTV-2 Parotid Brainstem CTV-1 Treating moving targets with protons Spinal Cord GTV 76 Gy CTV1 60-66 Gy CTV2 60 Gy 7/28/2008 15 Nodes 54 Gy 7/28/2008 16 4

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 7/28/2008 18 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 7/28/2008 19 No double scattering system No modulator wheels No aperture No range compensator 7/28/2008 20 5

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 7/28/2008 21 Pedroni Eros Pedroni, PSI 7/28/2008 22 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 7/28/2008 23 Alfred Smith, MDACC T axis profile Measurement vs. Calculation 7/28/2008 24 PTCOG 46 Educational Workshop Pedroni, PSI, Switzerland Alfred Smith, MDACC 6

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) 7/28/2008 25 Alex Trofimov, MGH 7/28/2008 26 Intensity-Modulated Proton Therapy IMPT Treatment Planning Passive scattered proton beams Scanned proton beams Intensity modulated proton beams Comparative treatment plans 7/28/2008 27 Alex Trofimov, MGH 7/28/2008 28 7

Example (passive scattered protons vs. photons) Protons Medulloblastoma Photons Medulloblastoma 7/28/2008 29 7/28/2008 Copyright MGH/NPTC 2003 30 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] 7/28/2008 31 Alex Trofimov, MGH 7/28/2008 32 8

Example (protons / IM protons / IM photons) Nasopharynx (case shown earlier) 7/28/2008 33 7/28/2008 34 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 7/28/2008 35 7/28/2008 36 Alex Trofimov, MGH Alex Trofimov, MGH 9

C IMPT plan (4 coplanar proton beams) DVH for target structures Comparable target coverage 7/28/2008 37 7/28/2008 38 Alex Trofimov, MGH Alex Trofimov, MGH DVH for some critical structures Summary 7/28/2008 39 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 7/28/2008 40 10

Some remarks on biology Integral dose (protons vs. photons) Neutrons in proton therapy The proton RBE 7/28/2008 41 Advantage protons!!! Dis-advantage protons??? 7/28/2008 42 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

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 ) 7/28/2008 45 NCRP Report No. 104, The Relative Biological Effectiveness of Radiations of Different Quality 7/28/2008 46 RBE in proton therapy: RBE values in vivo (center of SOBP; relative to 60 Co) 2.5 Clinical (generic) RBE = 1.1* RBE 2.0 1.5 1.0 1.07 0.12 * Based on experiments at the Harvard cyclotron done in the 70 s 7/28/2008 47 0.5 1 10 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, 407-421 7/28/2008 48 12

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 7/28/2008 49 RBE as a function of particle energy / LET Radiation is more effective when energy depositions are more concentrated in space p+ 7/28/2008 50 M. Krämer, W. K. Weyrather, M. Scholz: Techn. Cancer Res. Treatm. 2, 427-436, 2003 Thanks to Hanne Kooy Alex Trofimov George Chen Martijn Engelsman Judy Adams for providing some slides and figures 7/28/2008 51 13