CyberKnife: Treatment Planning and Delivery Capabilities

Transcription

1 CyberKnife: Treatment Planning and Delivery Capabilities Donald A. McRae, Ph.D. Department of Radiation Medicine Georgetown University Hospital

2 CyberKnife System

3 gun deck X-ray source magnetron Accelerating waveguide 9 GHz cables to modulator in separate room Image detectors

4 Cone set: 5mm 60 mm diameter beams at 80 cm

5 Cone Factor Comparisons GUH output factor compare Output Factor GUH Miami UCSF Vicenza BRMC collimator mm PTW 1 mm 2 diode adopted as standard

6 Radiation Characteristics

7 Beam profiles from which Off-Axis Ratios are obtained OAR 7.5, 15, 60 mm diam. collimators r (mm) No flattening filter, open air chambers

8 ~ 120 robot beam delivery points (called nodes) As the treatment progresses, the robot walks through a set of nodes in sequence. This is referred to as a path.

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10 nodes path Beams: 12 possible/node lesion Courtesy J. Rodgers

11 3D-non non-isocentric: CyberKnife

12 TREATMENT PLANNING FUSION CAPABILITIES CT/MR CT/PET

13 CONTOURING Fusions and contouring may be done on any TPS with DICOM export and the CT and contours imported into the CyberKnife The CT anatomy is the basis for treatment planning and all subsequent targeting CavS meningioma

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15 Inverse planning has two steps: Conformal Shape Inverse Planning 1. Beam Geometry Algorithm Create a list of all voxel elements along the boundary of each lesion and use this to create a list of all possible target points on the boundary.. For each of the possible ~1200 beams, the algorithm randomly selects one of the target points to aim at. 2. Optimization of beam weights by inverse planning The Treatment Planning System solves a linear optimization problem to determine beam weights with the following goal:: Minimize the total MU delivered during treatment, subject to minimum and maximum absorbed dose constraints in the lesions and maximum absorbed dose constraints in the critical structures. This optimization is solved with Simplex linear programming. One disadvantage is the inability to assess progress towards a solution as you can in typical IMRT inverse planning.

16 Beams returned from an optimization run Cav Sinus meningioma

17 Dose calculation The standard algorithm uses a ray-tracing function based on stored beam TMR data, off-axis ratios (OAR) and an output factor for the collimator(s) CF, At each point, the contribution from each beam is given by the equation: d = (SAD/800) -2 * CF * TMR * OAR * MU, where SAD is the source axis distance, along the central axis of the beam, to the point of the dose calculation, and MU is the number of monitor units for the beam. Contour corrections can be implemented for beams which enter the surface at oblique angles or graze the surface. Tissue density corrections are made by the simple path-length method. CT densities for air and lung are defined for this purpose.

18 Complex Benign Skull Base Lesion Cavernous sinus meningioma

19 DVH

20 Another complex benign lesion Acoustic Neuroma

21 Results for Complex Benign Skull Base Tumors Complex lesions defined: intricate threedimensional shape and spatial entanglement with one or more critical structures. (N=27) The mean tumor volume was Prescription IDL: 79.5(±6)%; 8.46 cm 3 (range: cm 3 ). Tumor coverage: 95 (±3.7)%;( NCI: 1.7 (±0.3)( [range ], CI: 1.6 (±0.3)( and HI: 1.26 (±0.1).( NCI = TV*PIV TIV is ideal in this scheme Neither tumor growth nor adverse effects have been noted in any patients during follow up.

22 Multiple Lesions

23 BEAM POINTING Two or more lesions may be treated at the same time

24 Clival Chordoma/ Graves Ophthalmopathy Deliver: Chordoma: 700cGy x 5 and 30% of that to Graves areas

25 Clival Chordoma/ Graves Ophthalmopathy

26 Clival Chordoma/ Graves Ophthalmopathy Chordoma: 700cGy x 5 to 80%IDL, 93% coverage. Deliver 30% to Graves areas

27 Extracranial: e.g. Spinal lesions

28 Spinal lesion volumes Volumes (cc) Spinal Lesion Volumes Series1 A tremendously diverse collection of tumor sizes, shapes, locations, and juxtapositions to the spinal cord and other critical structures were encountered. Most have had previous external beam. Mean volume 109±131 cc Range cc, Mean length along the cord: 57 mm (9-141mm); Mean closest distance to cord (not canal): 3.2 mm (0-11mm).

29 H y p o f r a c t i o n a t i o n Spinal radiosurgery starting point guide-lines for target peripheral doses Dose/fraction (cgy) Fractions Examples of use Untreated spine: (met. breast, thyroid, colon, renal, bladder, gross melanoma, squamous, small cell lung) Unresected chordoma, chondrosarcoma, osteogenic sarcoma Resected (microscopic disease remaining) chordoma, chondrosarcoma, osteogenic sarcoma Retreatment of spinal lesions after external beam (met. renal, nsc lung, sc lung, breast, giant cell, melanoma, colon, cervix, adenocarcinoma, bladder) Microscopic disease of resistant histology (renal, prostate, melanoma, adenocarcinoma, adenoid cystic) Gross disease of less resistant histology, (leukemia, lymphoma) Benign spinal lesions (neuroma, schwannoma, meningioma, hemangioma, ependymoma)

30 An example demonstrating a case close to the mean statistics TV = 67 cc; Min. distance to SC= 3mm Rx: 75% IDL 93% coverage, NCI = mm collimator, 303 beams

31 Spinal AVM

32 Lesion Tracking On Treatment

33 Lesion Tracking On Treatment The angles used for tracking on the CyberKnife are ±45 R and L lateral obliques. Anterior Right Left Posterior

34 CRANIAL TRACKING On treatment, the dynamic tracking system periodically obtains two orthogonal x-ray images of the patient and compares them with DRRs from the treatment planning. This yields the translational and rotational correction values needed to align the two. During treatment these values are transmitted to the robot to perform adaptive targeting to account for these patient position changes.

35 Fiducial Tracking (a) (b) Examples of fiducials as seen in tracking images: (a) near optimal and (b) among spinal hardware, but still trackable.

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37 Skeletal structure tracking

38 Early set-up image comparison

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40 Synchrony Respiratory motion tracking First Step: Fiducial Placement

41 Spiral Breath-hold hold Treatment Planning CT Planning proceeds in the normal way, except that Motion Tracking is selected.

42 Patient Garment with LED markers

43 Synchrony Respiratory Tracking System

44 Synchrony how does it work? Beacons on skin obtain instantaneous respiratory motion. X-ray snapshots of internal position of fiducials are made. A model is built correlating the instantaneous surface position to fiducial (tumor) location. The Robot aims the beam at the tumor at all times based on the surface motion and model.

45 Synchrony Graphical User Interface

46 Technology Concept External chest position red light beacons Internal gold fiducials

47 REAL BREATHING BEING TRACKED

48 Radiographs Pre and Post Treatment Pre-TX: 1 Week Post Tx 4 Weeks Post Tx

49 Prostate Treatment: CK boost

50 IDL (feet first orientation)

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52 Prostate Radiosurgery Tracking

53 Extremities For s rigid immobilization of the extremity, each patient was fitted with a personalized fiberglass cast. Each cast was bi-valved to allow for easy removal between treatments. This decreased the risk of loss of joint mobility during treatment. s

54 Left foot of patient with resected synovial sarcoma in bi-valved cast: the five gold seeds inserted into the cast are easily visualized.

55 Quality Assurance Isocrystal Pointing Accuracy Calibration and Testing

56 End-to-End Test Alignment of the film with the edges of the cube is crucial

57 End-to-End Film Analysis Program

58 End-to-end tests Final results at commissioning March 2002; Targeting error as total displacement: 6-D skull tracking: 0.44 mm,.73 mm for Bicron and CIRS skull tracking phantoms, resp. 6-D fiducial tracking: 0.63 mm CIRS body phantom. Results from June 2002, 3 month QA: Type * Par. Par Orth. Orth. Par Avg. SD (rms) 6-D Skull (mm) 6-D Fiducial (mm)

59 Monthly TLD dose delivery check Adjacent slices showing TLDs in phantom The treatment is set up using CK image tracking and delivered as a patient treatment. Results average within 5% of predicted.

60 Month/Year Reporting: FY : 7/1/05-thru most rece Day One (3/12/02) thru most recent Synchrony Synchrony Intracranial Sites Treated # of Sites # of Stages cases # of Sites # of Stages cases AVM/AVOM 7 7 Trigeminal Neuralgia 4 4 Acoustic Neuroma Meningioma Pituitary Adenoma Pineal Region Tumor 2 8 Glioblastoma GBM Craniopharyngioma Hemangioblastoma 4 12 Chordoma Schwannoma 2 10 Other/Vas/Func Benign Tumors Lung Met Liver Met 2 5 Breast Met Renal Met Colon Met 8 22 Melanoma Met Prostate Met 4 7 Pancreas Met 1 5 Ovarian Met 1 5 Other Metastatic Tumor Unknown Metastatic Tumor 6 20 Chondrosarcoma Glomus Tumor Other Primary Tumor 3 15 Astrocytoma/Glioma Ependymoma 4 16 Oligodendroglioma/Medulloblastom Hemangiopericytoma 2 6 Extracranial Sites Treated # of Sites # of Stages Synchrony # of Sites # of Stages Synchrony C-spine T-spine L/S-spine Lung Liver Pancreas Colon 1 5 Bone Head/Neck/ENT Prostate Nasopharynx Other Total Extracranial Treated TOTAL TREATED

61 The CyberKnife Team Radiation Oncology Gregory Gagnon, MD Brian Collins, MD K. Wm. Harter, MD Jeff Moulds, MD Anatoly Dritschilo, MD Physics Donald McRae, PhD Sonja Dieterich, PhD Huaying Ji Frank Xia,, PhD Surya Neupane Neurosurgery Therapy Walter Jean, MD Patricia Kornegay,, RTT Fraser Henderson, MD Gerard Elie,, RTT Christopher Kalhorn,, MD Sosena Asrat,, RTT Kevin McGrail,, MD T. Bertram Tucker, RTT

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