Practical Challenges and Opportunities for Proton Beam Therapy. M. F. Moyers Loma Linda University Medical Center

Transcription

1 Practical Challenges and Opportunities for Proton Beam Therapy M. F. Moyers Loma Linda University Medical Center

2 Outline I. Introduction II. Registration and Immobilization III. Beam Shaping IV. Localization V. Uncertainties, Margins, and Motion VI. Interoperability VII. Summary

3 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 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 Moyers, M. F. "LLUPTF: eleven years and beyond" Nuclear Physics in the 21st Century (New York: American Institute of Physics, 2002) p 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

4 LOMA LINDA UNIVERSITY MEDICAL CENTER COMPLETED PROTON PATIENT SUMMARY FROM INCEPTION THROUGH JANUARY TO MARCH 2003 DIAGNOSIS CATEGORY TOTAL % 1 Choroidal Melanoma % 2 Pituitary % 3 Acoustic Neuroma % 4 Meningioma % 5 Astrocytoma % 6 Other Brain % 7 Head & Neck % 8 Prostate % 9 Other Pelvis % 10 Craniopharyngioma % 11 Orbital % 12 Paraspinal Tumors % 13 Chordoma/Chondrosarcoma % 14 Sarcoma % 15 Other Chest % 16 AVM % 17 Other Abdominal % 18 SNVM % TOTAL BY YEAR , %

5 Conformal Avoidance Therapy Cerebro-spinal Irradiation standard protons standard x rays

6 Fraction of Volume Fraction of Volume Heart Dose (Gy) Thyroid Fraction of Volume Esophagus Dose (Gy) Vertebral Body Fraction of Volume Dose (Gy) Bowel Dose (Gy) Fraction of Volume DVHs: Dose (Gy) pink - standard x rays blue - standard protons

7 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

8 Standard Headrest and Facemask Frame

9 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

10 Headrest Perturbations (Wake Effect) 0 o and 10 o Incidence CAX support CAX support

11 16 Penumbra Example 149 MeV - Center of Modulation at Isocenter % Penumbra Width [mm] mm bolus, ApID = 380 mm 38 mm bolus, ApID = 380 mm no bolus, ApID = 380 mm no bolus, ApID = 210 mm Bolus Thickness + Patient Depth [mm water]

12 Flat Table Top Perturbation from table edge Large gap between aperture/bolus and patient resulting in large penumbra

13 Whole Body Pod minimize perturbation from edge minimize gap between aperture/bolus and patient resulting in smaller penumbra

14 Picture of Pod with C-arms

15 Aperture and Aperture Frame Bolus and Bolus Frame

16 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

17 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

18 Snout Extension with Pre-collimator Plates and Exchangeable Cone

19 Multi-leaf Collimator (Chiba) eliminates lifting of heavy apertures provides ability to do IMPT

20 Prostate Field using MLC (Berkeley MLC and LLUMC proton beam) surface 29 cm deep 26 cm scattering diameter

21 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

22 Modulator Propellors 43 cm diameter 11 cm diameter large beam small beam mid-nozzle nozzle entrance

23 Ridge Filters (Kashiwa)

24 Dynamic Scattering System

25 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

26 Film of Small Spot Scan

27 Orthogonal X Ray Tubes and Imagers on Rotating Gantry (Hyogo) extended retracted

28 Alignment in Tx Room Using Orthogonal Pairs of DRRs and Electronic Images Identical landmarks identified on treatment planning DRRs and treatment room images.

29 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.

30 Authorization to Treat precision treatments use small margins from tumors and critical structures therapist versus MD versus computer algorithm turnaround time

31 Proton Beam Treatment Planning - General Comments Planning is the core of proton beam therapy. The devil is in the details.

32 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 Battista et al 1980 fit MGH model c1980 LLUMC model 1996 Moyers et al 1992 measured Schneider et al 1996 calculated Scaled CT Number

33 Relative Linear Stopping Power Assignments registration / immobilization devices gas bubbles contrast agents metal implants artifacts tissue motion

34 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)

35 Motion Example: Moving Target Solution: expand aperture, design target for bolus with WE of bolus target set to match real target tissue

36 Motion Example: Moving Normal Tissue Solution: replace tissue volume with highest density tissue

37 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

38 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

39 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