Practical Challenges and Opportunities for Proton Beam Therapy M. F. Moyers Loma Linda University Medical Center
Outline I. Introduction II. Registration and Immobilization III. Beam Shaping IV. Localization V. Uncertainties, Margins, and Motion VI. Interoperability VII. Summary
References Moyers, M. F. Proton Therapy The Modern Technology of Radiation Oncology: A Compendium for Medical Physicists and Radiation Oncologists ed. van Dyk, J. (Wisconsin: Medical Physics Publishing, 1999) p. 823-869. Moyers, M. F. Miller, D. W. Bush, D. A. Slater, J. D. Slater, J. M. Methodologies and tools for proton beam design for lung tumors International Journal of Radiation Oncology, Biology, Physics 49(5) (2001) p. 1431-1440. Moyers, M. F. "LLUPTF: eleven years and beyond" Nuclear Physics in the 21st Century (New York: American Institute of Physics, 2002) p. 305-309. Shanazi, K. Moyers, M. F. Yuh, G. Miller, D. Slater, J. Loredo, L. "Cerebrospinal irradiation using proton beams for the treatment of medulloblastoma" Medical Physics 29(6) (2002) p. 1216.
LOMA LINDA UNIVERSITY MEDICAL CENTER COMPLETED PROTON PATIENT SUMMARY FROM INCEPTION THROUGH JANUARY TO MARCH 2003 DIAGNOSIS CATEGORY 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 TOTAL % 1 Choroidal Melanoma 3 7 13 4 13 8 8 13 9 1 10 13 16 3 121 1.5% 2 Pituitary 10 17 6 5 1 7 2 2 7 6 13 2 78 1.0% 3 Acoustic Neuroma 3 3 0 3 3 4 2 2 9 7 10 10 1 57 0.7% 4 Meningioma 8 16 8 8 7 7 19 12 9 17 9 9 1 130 1.6% 5 Astrocytoma 4 26 4 6 5 17 9 7 10 13 18 11 130 1.6% 6 Other Brain 6 6 7 9 15 3 17 31 36 41 30 39 9 249 3.1% 7 Head & Neck 3 26 20 26 27 49 41 43 55 65 75 64 6 500 6.2% 8 Prostate 4 198 234 234 308 476 507 631 447 491 649 694 193 5066 63.1% 9 Other Pelvis 1 8 10 4 0 8 3 8 5 7 12 15 3 84 1.0% 10 Craniopharyngioma 0 3 0 1 1 2 4 4 2 2 19 0.2% 11 Orbital 3 2 0 0 1 2 11 13 12 0 5 4 53 0.7% 12 Paraspinal Tumors 1 11 8 6 4 7 7 12 15 14 18 10 1 114 1.4% 13 Chordoma/Chondrosarcoma 0 13 26 21 25 28 38 51 44 34 40 50 8 378 4.7% 14 Sarcoma 3 3 3 12 2 4 8 15 9 17 4 10 2 92 1.1% 15 Other Chest 0 0 7 11 34 16 34 44 27 49 46 49 6 323 4.0% 16 AVM 1 31 17 14 6 21 12 12 11 4 4 133 1.7% 17 Other Abdominal 5 7 9 4 9 23 13 23 21 5 119 1.5% 18 SNVM 21 29 20 35 30 57 101 57 27 3 380 4.7% TOTAL BY YEAR 3 53 345 338 416 494 681 760 944 780 899 1033 1035 245 8,026 100.0%
Conformal Avoidance Therapy Cerebro-spinal Irradiation standard protons standard x rays
Fraction of Volume Fraction of Volume 1.2 1 0.8 0.6 0.4 0.2 0 1.2 1 0.8 0.6 0.4 0.2 Heart 0 5 10 15 20 25 30 35 Dose (Gy) Thyroid Fraction of Volume 1.2 1 0.8 0.6 0.4 0.2 0 1.2 1 Esophagus 0 5 10 15 20 25 30 35 40 Dose (Gy) Vertebral Body Fraction of Volume 0 0 5 10 15 20 25 30 35 Dose (Gy) Bowel 1.2 1 0.8 0.6 0.4 0.2 0 0 10 20 30 40 Dose (Gy) Fraction of Volume 0.8 0.6 0.4 0.2 0 0 5 10 15 20 25 30 35 40 45 DVHs: Dose (Gy) pink - standard x rays blue - standard protons
The Caveat of Proton Beam Therapy More precise but less forgiving than x rays and electrons» sharper lateral gradient» sharper distal gradient» lower integral dose» if miss-used, can lead to geometrical miss of target» if miss-used, can damage normal tissue» if target unknown, can lead to geometrical miss of target
Standard Headrest and Facemask Frame
Problems with Standard Headrest and Facemask Frame magnified FOV CT circle does not include table top and mask frame preventing design of bolus common headrest shape does not conform to individual patient resulting in patient discomfort and fulcrum points for motion support sides of common headrest produce large perturbations in proton dose distribution facemask frame produces large perturbations in proton dose distribution large skin-to-aperture distance results in large penumbra
Headrest Perturbations (Wake Effect) 0 o and 10 o Incidence CAX support CAX support
16 Penumbra Example 149 MeV - Center of Modulation at Isocenter 80-20 % Penumbra Width [mm] 12 8 4 76 mm bolus, ApID = 380 mm 38 mm bolus, ApID = 380 mm no bolus, ApID = 380 mm no bolus, ApID = 210 mm 0 0 20 40 60 80 100 120 140 Bolus Thickness + Patient Depth [mm water]
Flat Table Top Perturbation from table edge Large gap between aperture/bolus and patient resulting in large penumbra
Whole Body Pod minimize perturbation from edge minimize gap between aperture/bolus and patient resulting in smaller penumbra
Picture of Pod with C-arms
Aperture and Aperture Frame Bolus and Bolus Frame
Bolus and Aperture Requirements minimize skin-to-aperture distance» penumbra versus air gap minimize scatter» penumbra versus thickness of bolus minimize weight» lifting restrictions for therapists accurately place into beamline» lateral margin
Methods to Satisfy Bolus and Aperture Requirements exchangeable cones for different field sizes» similar to electron cones» scatter or scan beam only to final size successive stages of pre-collimator trimmers and a final patient aperture aperture thickness split into several layers that are installed separately large number of accelerator energies» portal specific energy extendable snout multi-leaf collimator
Snout Extension with Pre-collimator Plates and Exchangeable Cone
Multi-leaf Collimator (Chiba) eliminates lifting of heavy apertures provides ability to do IMPT
Prostate Field using MLC (Berkeley MLC and LLUMC proton beam) surface 29 cm deep 26 cm scattering diameter
Depth Profiling Techniques (Range Modulation) TECHNIQUE LOCATION COMMENTS energy stacking accelerator a. no mechanical movements, no generation of neutrons d. accelerator retuning, switchyard retuning, scatterer adjustment rangeshifters accelerator exit a. no accelerator retuning d. switchyard retuning, lower dose rate at lower energies, generation of neutrons, scatterer adjustment nozzle entrance a. no accelerator retuning, no switchyard tuning d. lower dose rate at lower energies, generation of neutrons, scatterer adjustment nozzle exit a. no accelerator retuning, no generation of neutrons, no scatterer adjustment d. increased penumbra propellors nozzle middle a. easy to make, no scatterer adjustment nozzle entrance ridge filters nozzle middle a. time independent d. difficult to make d. installed by hand, easy to break a. small, automatically installed d. complex design to compensate for scattering
Modulator Propellors 43 cm diameter 11 cm diameter large beam small beam mid-nozzle nozzle entrance
Ridge Filters (Kashiwa)
Dynamic Scattering System
Scanning Definitions Wobbling: a non- or slowly-repeating pattern» ex. circular with modulating radius - perpendicular sine waves with identical frequencies 90 o out of phase» ex. Lissajous - perpendicular triangle waves of different frequencies (non-multiple) Raster: a spatially and temporally constant scan pattern pre-defined for use with all patients» ex. repeating triangle wave» ex. rectilinear Spot: a customized scan pattern for an individual patient defined spatially and or temporally
Film of Small Spot Scan
Orthogonal X Ray Tubes and Imagers on Rotating Gantry (Hyogo) extended retracted
Alignment in Tx Room Using Orthogonal Pairs of DRRs and Electronic Images Identical landmarks identified on treatment planning DRRs and treatment room images.
Alignment in Tx Room Using Orthogonal Pairs of DRRs and Electronic Images Aperture projection with x ray magnification also transmitted for comparison with double exposure. Alignment algorithm calculates translations and rotations.
Authorization to Treat precision treatments use small margins from tumors and critical structures therapist versus MD versus computer algorithm turnaround time
Proton Beam Treatment Planning - General Comments Planning is the core of proton beam therapy. The devil is in the details.
XCT 2.0 CT# versus tissue» scanner dependent» protocol dependent (FOV, kvp, slice width, filter)» patient specific scaling CT# to proton RLSP conversion curve Relative Linear Stopping Power 1.5 1.0 0.5 Battista et al 1980 fit MGH model c1980 LLUMC model 1996 Moyers et al 1992 measured Schneider et al 1996 calculated 0.0 0 500 1000 1500 2000 2500 3000 Scaled CT Number
Relative Linear Stopping Power Assignments registration / immobilization devices gas bubbles contrast agents metal implants artifacts tissue motion
Margins and Uncertainties target coverage» CTV only, no PTV normal tissue avoidance lateral penumbra lateral alignment uncertainty» target, 90% (1.5 σ)» normal, average position distal gradient penetration uncertainty» target, 90% (1.5 σ)
Motion Example: Moving Target Solution: expand aperture, design target for bolus with WE of bolus target set to match real target tissue
Motion Example: Moving Normal Tissue Solution: replace tissue volume with highest density tissue
Interoperability XCT Treatment Planning System home grown Aperture Manuf. Bolus Manuf. Beam Delivery System Positioner Imager home home home grown grown grown Optivus ABB Trixell GE home Fanuc grown Siemens Permedics Par Scientific Toshiba CMS Huestis IBA Siemens Perkin- Elmer Phillips MDS- HEK Hitachi Oncolog Cares Nordion Built Shimadzu Varian Fanuc Mitsubishi IBA Accel Mitsuibishi Hitachi
DICOM-RT WG-7 Ion Beam Sub-Group Dec, 1999 Varian proposal to add tags to support protons Aug, 2000 LLUMC proposal to define and test parallel RT Proton Beam Module that would later be incorporated into standard RT Beams Module Feb, 2000 WG-6 proposal for RT Ion Plan Object parallel to RT Plan Object Jul, 2001 formation of Ion Beam sub-committee of DICOM WG-7 Nov, 2001 first formal meeting of ion beam sub-committee at NEMA headquarters in Arlington May, 2002 second formal meeting in conjunction with PTCOG meeting in Cantania throughout numerous telephone and web conferences
Summary reduce motion and assure repeatable set-ups avoid edges within beam path avoid objects that do not lie on the CT conversion curve minimize air gaps between beamline devices and patient minimize bolus thickness or rangeshifter thickness at patient explicitly account for lateral and penetration uncertainties on a beam by beam basis explicitly account for penumbra and distal gradient on a beam by beam basis avoid collisions with localization devices provide communication between devices involved in planning and delivering treatments