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HST.187: Physics of Radiation Oncology #5. Intensity-modulated radiation therapy: IMRT and IMPT Part 2: IMPT Joao Seco, PhD Alexei Trofimov,

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Presentation on theme: "HST.187: Physics of Radiation Oncology #5. Intensity-modulated radiation therapy: IMRT and IMPT Part 2: IMPT Joao Seco, PhD Alexei Trofimov,"— Presentation transcript:

1 HST.187: Physics of Radiation Oncology #5. Intensity-modulated radiation therapy: IMRT and IMPT Part 2: IMPT Joao Seco, PhD Alexei Trofimov, PhD Dept of Radiation Oncology MGH March 6, 2007

2 IMRT Coll. Work Group IJROBP 51:880 (2001) IMRT is a treatment technique with multiple fields, where each field is designed to deliver a non-uniform dose distribution.The desired (uniform) dose distribution in the target volume is obtained after delivery of all treatment fields. Flexible field definition, sharper dose gradients Higher dose conformity Improved sparing of healthy tissue

3 Protons vs. Photons Ideal

4 Intensity Modulated Proton Therapy IMPT = IMRT with protons

5 Intensity Modulated Proton Therapy Planning approaches Delivery options (inc. MGH plan) Overview of IMPT treatments / development Special considerations for IMPT IMPT vs. 3D-conformal proton vs. photon IMRT in the clinic

6 Proton depth-dose distribution: Bragg peak Depth = additional degree of freedom with protons H.Kooy BPTC

7 A. Lomax: Intensity modulation methods for proton RT Field incidence Distal Edge Tracking Field incidence 2D modulation Field incidence 2.5 D modulation Field incidence 3D modulation Phys. Med. Biol. 44: (1999)

8 IMPT – Example 1 (distal edge tracking)

9 IMPT – Example 2 (3D modulation)

10 Treatment planning for IMPT: KonRad TPS (DKFZ) - Bragg peaks of pencil beams are distributed throughout the planning volume - Pencil b eam weights are optimized for several beam directions simultaneously, using inverse planning techniques - Output of optimization: beam weight maps for diff energies

11 Intensity Modulated Proton Therapy Planning approaches Delivery options (MGH plan, other sites) Overview of IMPT treatments / development Special considerations for IMPT IMPT vs. 3D-conformal proton vs. photon IMRT in the clinic

12 IMRT delivery with multi-leaf collimators

13 A proton pencil beam Proton IMPT with Scanning E.Pedroni (PSI) Protons have charge can be focused, deflected (scanned) magnetically!

14 A layer is irradiated by scanning a pencil beams across the volume Proton IMPT with Scanning E.Pedroni (PSI)

15 Several layers are irradiated with beams of different energies Proton IMPT with Scanning E.Pedroni (PSI)

16 Complete treatment: a homogenous dose conformed distally and proximally Proton IMPT with Scanning E.Pedroni (PSI)

17 : pencil beam scanning nozzle for MGH Continuous scanning. Modulation in current and speed. Pencil beam spot width ( ) at the isocenter: ~4-10 mm Several identical paintings (frames) of the same target slice (layer) Max patient field (40x30) cm 2 Beam monitor Intensity Modulated Beam Z X Y Fast Slow Scanning Magnets Pair of Quads Vacuum Chamber

18 Beam delivery: continuous magnetic scanning in 2D Beam fluence variation along the scan path is achieved by simultaneously varying the beam current and scanning speed: Actual scan is ~50 times faster (0.4 sec)

19 Scan functions: degeneracy of the solution

20 Intensity Modulated Proton Therapy Planning approaches Delivery options (MGH plan, other sites) Special considerations for IMPT Overview of IMPT treatments / development IMPT vs. 3D-conformal proton vs. photon IMRT in the clinic

21 The effect of delivery uncertainties in IMPT: fluctuations in the beam position during the scan planned dose distr dose difference due to flucts plan delivery

22 Beam size in IMPT S Safai

23 Proton dose in the presence of range uncertainty

24 Proton dose in the presence of range uncertainty (a dense target) Lower proton dose

25 IMPT – DET (Distal Edge Tracking) Tumor T. Bortfeld

26 Distal Edge Tracking: Problem with range uncertainty Tumor Brainstem T. Bortfeld

27 In-vivo dosimetry / range verification with PET K. Parodi (MGH) MGH Radiology

28 IMPT in the presence of range uncertainties: DET vs. 2.5D DET DET (+1 mm) DET (+3 mm) DET (+5 mm) 2.5D 2.5D (+1 mm) 2.5D (+3 mm) 2.5D (+5 mm)

29 Robust IMPT optimization Phantom test case Standard optimization Robust optimization J Unkelbach (MGH)

30 Degeneracy of IMRT solution: different modulation patterns may produce clinically equivalent dose distributions

31 Proton Treatment Field Brass Collimator M Bussiere, J Adams

32 Scanning with a range compensator

33 Scanning and IMPT Is scanning = intensity-modulation ?

34 IMPT delivery: Spot scanning at PSI (Switzerland) A Lomax Med Phys (2004)

35 PSI gantry radmed.web.psi.ch/asm/gantry/intro/n_intro.html Gantry radius 2m Rotation 185 deg Step-and-shoot scanning: 200 MeV proton beam is stopped at regular intervals, no irradiation between beam spots magnets range shifter beam monitor sweeper quad

36 PSI ProSCAN

37 Scanning and IMPT Is scanning = intensity-modulation ? Is beam scanning = IMPT?

38 1 field SFUD – single field uniform dose Dose conformation with IMPT 1 field 3 fields 3D IMPT 3D-CPT 1 field 3 fields A Lomax (PSI) ?? 2.5-D IMPT ??

39 Scanning and IMPT Is beam scanning = IMPT ? Is scanning = intensity-modulation ? Is intensity-modulation = IMPT ?

40 Spread-Out Bragg Peak (SOBP) RM Wheel 10 / sec

41 Spread-Out Bragg Peak (SOBP) RM Wheel 10 / sec

42 Spread-Out Bragg Peak (SOBP) RM Wheel 10 / sec

43 Beam-current modulation: flat-top SOBP

44 Beam-current modulation: sharper fall-off

45 IMPT fields for a prostate treatment Double scattering IMPT

46 Intensity Modulated Proton Therapy Planning approaches Delivery options (MGH plan, other sites) Special considerations for IMPT Overview of IMPT treatments / development IMPT vs. 3D-conformal proton vs. photon IMRT in the clinic

47 Delivery of IMPT: Spot scanning at PSI (Switzerland) Since 1996: Combination of magnetic, mechanical scan Energy selection at the synchrotron + range shifter plates A Lomax Med Phys (2003)

48 GSI Darmstadt: scanned carbon beam D Shardt (GSI) © Physics World

49 GSI patient case: Head+Neck Carbon Proton (IMPT) Plan: O. Jaeckel (GSI) Plan: A.Trofimov (MGH)

50

51

52 Depth scanning at GSI (270 MeV C-ions) U.Weber et al. Phys.Med.Biol. 45 (2000) Weaknesses of lateral scanning: –complicated scanning pattern –need to interrupt the beam Depth scanning: –Target volume is divided into cylinders spaced at ~0.7 FWHM (or 4-5 mm) –Cylinders are filled with SOBP (or arbitrarily shaped distribution)

53 Scanning directions Fast scanning in depth (2 sec/cylinder) Slower lateral scanning (sweeper magnet) Yet slower azimuthal scanning (gantry rotation)

54 GSI: IMPT with depth scanning Same dose conformity as with lateral scanning A simpler, uninterrupted scanning pattern Treatment time a factor of 4 longer than with 2D raster scanning

55 Proton Therapy Center – MD Anderson CC, Houston Passive Scattering Ports Pencil Beam Scanning Port Large Field Fixed Eye Port Experimental Port Accelerator System PTC-H 3 Rotating Gantries 1 Fixed Port 1 Eye Port 1 Experimental Port Hitachi, Ltd. M. Bues (MDACC)

56 Basic Design Parameters for PBS at PTC-Houston Step and shoot delivery Minimum range: 4 cm Maximum range: 30 cm Field size: 30 x 30 cm Source-axis-distance: 250 cm Spots size in air, at isocenter: –4.5 mm for range of 30 cm –5 mm R=20 cm –6.5 mm R=10 cm –11 mm R=4 cm Varian Eclipse TPS Beam 3.2m Scanning Magnets Beam Profile Monitor Helium Chamber Position Monitor Dose Monitor 1, 2 Isocenter Hitachi, Ltd. M. Bues (MDACC)

57 Intensity Modulated Proton Therapy Planning approaches Delivery options (MGH plan, other sites) Overview of IMPT treatments / development Special considerations for IMPT IMPT vs. 3D-conformal proton vs. photon IMRT in the clinic

58 Clinical relevance of intensity-modulated therapy (protons vs photons) Conformality Integral dose high low high 3D CRT IMXT3D PT IMPT J Loeffler, T Bortfeld Complex anatomies/geometries (e.g., head & neck) with multiple critical structures Cases where Tx can be simplified, made faster Cases where integral dose is limiting (e.g., pediatric tumors) Cases where it may be possible to reduce side- effects (improve patients quality of life)

59 Comparative treatment planning 3D-CPT IMPT IMXT Dose [Gy/GyE] Purpose: to identify sites, tumor geometries that would benefit the most from a certain treatment modality or technique J Adams A Chan (MGH)

60 Nasopharyngeal carcinoma Clinical plan: composite proton+X-ray BPTC: 12 proton fields –CTV to 59.4 GyE (33 x 1.8 Gy) –GTV to 70.2 GyE (+ 6 x 1.8 Gy) MGH Linac: 4 fields (lower neck, nodes) to 60 Gy Case 1 N N G G J Adams A Chan (MGH)

61 IMXT plan For delivery on linac with 5-mm MLC –6 MV photons –7 coplanar beams Case 2

62 Bragg peak placement in 3D Proton beam energies: MeV 4 coplanar fields Case 3 IMPT plan

63 Dose-volume histograms (DVH) D 50 D5D5 D 95

64 Nasopharyngeal carcinoma: dose to tumor 3D-CPT IMPT IMXT Case 2 Comparable target coverage

65 (Some) common complications in Head+Neck Tx Compromised vision –Optic nerves, chiasm (tolerance: 54 Gy), eye lens (<10 Gy) Compromised hearing –Cochlea (<60 Gy) Dysphagia / aspiration during swallowing –Salivary glands: e.g. parotid (mean <26 Gy) –Larynx, constrictors, supraglottic, base of tongue –Suprahyoid muscles: genio-, mylohyoid, digastric Xerostomia (dry mouth) –Salivary glands Difficulty chewing, trismus –Mastication muscles: temporalis, masseters, digastric Compromised speech ability –Vocal cords, arytenoids, salivary glands

66 Dose-response models: e.g. parotid gland Saarilahti et al (Radiother Onc 2005) Eisbruch et al (IJROBP 1999) Roesink et al (IJROBP 2001)

67 Chao et al (IJROBP 2001) Complications may arise from irradiation to doses well below the organ tolerance Roesink et al. (IJROBP 2001)

68 Treatment planning for nasopharyngeal carcinoma Critical normal structures (always outlined): –brain stem, spinal cord, optic structures, parotid glands, cochlea Extra structures were outlined on 3 data sets –esophagus, base of tongue, larynx –minor salivary, sublingual and submandibular glands –mastication and suprahyoid muscles

69 Nasopharyngeal carcinoma: sparing of normal structures Superior sparing with protons –Brainstem –Suprahyoid muscles –Sublingual, minor salivary glands

70 Nasopharyngeal carcinoma: sparing of normal structures (2) IMXT/IMPT better than 3D-CPT –Salivary glands –Supraglottic structures

71 IMPT may further improve sparing –Mastication muscles –Oral cavity, palate, base of tongue –Cochleae –Optic structures, temporal lobes Nasopharyngeal carcinoma: sparing of normal structures (3)

72 IMPT may further improve sparing –Mastication muscles –Oral cavity, palate, base of tongue –Cochleae –Optic structures, temporal lobes Nasopharyngeal carcinoma: sparing of normal structures (4)

73 Retroperitoneal sarcoma C. Chung, T.Delaney Radiation dose: 50.4 Gy (E) in 1.8 Gy/fx to 100% of CTV and 95% of PTV Pre-op Boost of 9 Gy (total 59.4 Gy (E)) Post-op Boost of 16.2 Gy (total 66.6 Gy (E)) Organ at Risk (OAR) constraints Liver: 50% < 30 GyE Small Bowel: 90% < 45 GyE Stomach, Colon, Duodenum: max 50 GyE Kidney: 50% < 20 GyE

74 36 yo M with myxoid liposarcoma:Transverse IMXT (photon IMRT) 3D CPT IMPT

75 36 yo M with myxoid liposarcoma: Sagittal IMXT 3D CPT IMPT

76 Boost IMXT IMPT

77 PTV Conformity Index (CI)= V 95% / PTV Range (N=10)Mean IMXT1.19 – D CPT1.37 – (p=0.032) IMPT1.05 – (p=0.005)

78 D mean to OAR D mean to liver (n=8) Preop boost (n=3) IMXT0.94 – 24.6 Gy, mean 11.8 Gy 12.0 – 24.6 Gy, mean 16.7 Gy 3D CPT0.01 – 20.9 Gy, mean 6.61 Gy (p=0.01) _____ IMPT0.99 – 18.6 Gy, mean 5.73 Gy (p=0.03) 2.8 – 18.6 Gy, mean 9.2 Gy

79 D mean to OAR (2) D mean to stomach (n=8) Preop boost (n=3) IMXT4.03 – 44.2 Gy, mean 15.4 Gy 13.3 – 43.6 Gy, mean 28.4 Gy 3D CPT0 – 50.0 Gy, mean 11.8 Gy (p=NS) _____ IMPT0 – 36.5 Gy, mean 7.85 Gy (p=0.02) 3.5 – 35.2 Gy, mean 16.8 Gy

80 Prostate carcinoma: (GTV + 5mm) to 79.2 Gy (CTV + 5mm) to 50.4 Gy 3D CPT IMRT IMPT

81 Prostate: IMRT vs 3D-CPT vs IMPT

82 Burr Proton Therapy Center (2001-) Patient Population Brain32% Spine 23% Prostate12% Skull Base12% Head & Neck 7% Trunk/Extremity Sarcomas 6% Gastrointestinal 6% Lung 1% T. DeLaney, MD

83 IMPT vs. photon IMRT More tumor-conformal dose: reduction in dose to healthy organs (including skin) (?) increased tumor control, reduced complications (acute and late). Proton integral dose smaller (factor 1.5-3) Proton dose conformality much better at low and medium doses, but usually equivalent to IMRT in high-dose range Treatment delivered with fewer fields (2-3 vs. 5-7); Patient-specific devices/QA are not strictly required more treatments at lower cost Precision of delivery can be increased with robust planning methods, in-vivo range/dose verification

84 Acknowledgements T Bortfeld, PhD GTY Chen, PhD T DeLaney, MD J Flanz, PhD H Kooy, PhD J Loeffler, MD JA Adams M Bussiere S McDonald, MD H Paganetti, PhD K Parodi, PhD S Safai, PhD H Shih, MD J Unkelbach, PhD Ion Beam Applications M Bues, PhD


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