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CYBERKNIFE SRS & SBRT
P.Mahadev MD DNB
Apollo Speciality Cancer Hospital
Chennai
MANAGEMENT AND DELIVERY OF IMAGE GUIDED HIGH DOSE RADIATION THERAPY WITH TUMOR ABLATIVE INTENT WITHIN A COURSE OF TREATMENT THAT DOES NOT EXCEED 5 DAYS
Higher confidence in tumor targeting
Reliable mechanisms for generating focused, sharply delineated dose distributions with a rapid dose fall off
Reliable accurate patient positioning accounting for target motion related to time dependent organ movement
IMAGE GUIDANCE AND EFFICIENT TRACKING MECHANISM
Longer times than conventional RT, hence patient comfort is an issue
SRSSBRTIMRT FOR PROSTATESRT
5
1
2
3
465
PitchRollYaw
Robot is capable of delivering radiation from different 100 nodes, with each node is capable of giving a maximum 12 different beams.
Usage of these nodes depends on the treatment room constraints
The table consists of 12 fixed cones and housings of Fixed and Iris Collimator
Collimator sizes(mm): 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50, 60
Laser Sensor
There are two essential features of the CyberKnife system that sets it apart from other stereotactic radiosurgery methods.
radiation source is mounted on a precisely controlled industrial robot.
The image guidance system(continuous tracking system)
Eliminates the need of gating techniques and restrictive head frames
The Cyberknife treatment delivery is based on the following tracking systems
6D_ Skull tracking systemFiducials tracking systemSynchrony tracking systemX_sight Spine tracking systemX_sight Lung tracking system
6D_ Skull tracking system:used for intra-cranial lesions up to C2Bony anatomy of the skull is used as reference for tracking
Fiducial tracking system:used for soft tissues, where gold fiducials can be implanted. Minimum of 3 nos. to be implanted
close proximity to the lesion to be treated
well-separated (by about 1 cm) non-overlapping on projections from the in-room x-ray imagers
Three markers are sufficient for unique spatial localization, but in practice 4-5 are often placed in case of loss or suboptimal placement of markers
• 790 fiducials• 85% successfully placed• 2 Patients developed
pneumothorax• 6 fiducials migrated- 3 in
lung, 2 in liver& 1 in prostate
Respiratory-induced motion of tumors causes significant targeting uncertainty Lung, liver, pancreas, Prostate,kidney
Traditional radiation therapy margins are not optimized for high-dose radiosurgery
Imaging and Tumor TargetingTraditional IGRT daily set-up imaging maybe inadequate for sub-millimeter accuracy
ImmobilizationBreath Holding
Imaging and Tumor TargetingTraditional IGRT daily set-up imaging maybe inadequate for sub-millimeter accuracy
ImmobilizationBreath HoldingGating
option for dynamic tracking without the use of implanted fiducials.
Tumor localization is accomplished using auto- mated real-time image segmentation of the in-room x-ray images based on the contrast of the tumor itself.
best used for lesions with sufficient contrast in density from the surrounding anatomy to be clearly visualized on both of the in-room x-ray imagers, i.e., those located in the lung periphery at least 1.5 cm in size, and that do not overlap other dense anatomical structures, such as the spine, diaphragm, and heart in the projection views
Two features to form the basis for accuracy
Fiducials, implanted prior to treatment
Optical markers on a special patient vest
Prior to treatment start: creation of dynamic correlation model
Markers are monitored in real time by a camera system
Imaging system takes positions of fiducials at discrete points of time
Prior to treatment start: creation of dynamic correlation model
Markers are monitored in real time by a camera system
Imaging system takes positions of fiducials at discrete points of time
time
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This process repeats throughout the treatment, updating and correcting beam delivery based upon the patient’s current breathing pattern
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X-sight Spine tracking system:used to track spine lesions which are close to spine from C1 to L5&sacrum
Uses the bony anatomy of spine to track the tumors in close relation to spine eliminating the need for fiducials
X-sight spine is now possible in prone position as well
The appropriate tracking method has to be chosen during planning itself
No treatment is possible without planning and proper tracking method
Treatment planning is done on the CT images of slice thickness 1mm acquired at 125 kV and 400 mAs with a pixel size of 512 x 512
MRI, PET and 3D-Angio images can be used to fuse with the primary CT images for target and OAR delineation
Planning System (MultiPlan) uses inverse planning algorithm with following options1. Conformal Planning2. Sequential optimizationThe system provides the user the option of using either ray tracing method or Monte Carlo
The mechanical accuracy of the system is 0.12 mm , according to Accuray
The system maintains sub-millimeter tracking accuracy, if the patient positions are within the following limitsLeft / Right (Lat) 10 mmAnt/ Post (Ver) 10 mmSup/ Inf ( Long) 10 mmRoll (Left / Right) 10
Pitch (Head Up / Down) 10
Yaw ( C.W / C.C.W) 30
The Robot will correct its position if the off set values are with in the specified limits
The robot will trigger an Emergency Stop outside of these tolerances
Gamma knife, X-knife are probably as good.
May have an advantage for larger lesions requiring multiple fractions- meningioma, acoustic schwanomma etc
More patient friendly(frame)Continuous image guidance
T1&T2 NSCLC – inoperable or medical contraindication or patient refuses surgery, ideal lesion <3cm & peripheral location
oligometastasis
in a uniform population of medically inoperable patients with peripherally located early lung cancer, the RTOG 0236 study dem- onstrated 98% local control (within the primary tumor) and 87% local-regional control (within the ipsilateral lobe, hilum, and mediastinum) at 3 years with an intensive regimen of 60 Gy in 3 fractions
RADIOBIOLOGICAL RATIONALE: LOW APLHA/BETA RATIO
GOOD RESULTS OBTAINED WITH HDR brachytherapy
LESS INVASIVE THAN BRACHYTHERAPY
Ju AW et al :Radiat oncol jan201341 pts intermediate riskMedian fu 21 mo99% biochemical PFSNo gr3/4 bladder or bowel morbidityNo significant change in sexual QOL
BRACHYTHERAPY: 10/10.5 Gy x3 over 24 hours, each fraction 8 hours apart
BED : 130/142 GySBRT : 7.25 Gy x5 over 5 daysBED: 123 Gy
T1 T2 PSA<10 PSA>10 GS<7 GS>7 TOTAL
HDR 30 22 35 17 40 12 52
CK 34 32 40 16 35 31 66
IMRT/IGRT
94 186 94 186 126 154 280
MEDIAN FU 2 YR BIOCHEMICAL PFS
MEDIAN PSA NADIR
HDR 22 MONTHS 94% 0.8
CK 16 MONTHS 96% 1.0
IMRT/IGRT 48 MONTHS 89% 0.9
Fiducials placed at surgeryOne planning CT with oral and IV contrast
1000cGy to +ve margins 3-4 weeks post OP
5040cGy 5-6 field IMRT6-8 weeks postOPConcurrent XelodaAdjuvant Gemcitabine
Intramedullary spinal cord AVM’s onlyNot amenable to microsurgical excision/embolisation
symptomatic
Neurologic examinationMRIConventional 2D spinal angio
Spine tracking1.25 mm contrast enhanced axial CTTarget volume traced on CT in cojunction with:MRI
2D/3D spinal angio
24 patients15 males 9 femalesTime from diagnosis to SRS:7.8 yrsMean age at SRS 34 YrsPresentation :12 hemorrhages
12 had progressive pain or myelopathy secondary to steal or venous congestion
13 cervical8 thoracic3 conus medullaris
Target volume :2.8cc(0.26-15 cc)Marginal nidus dose :2050cGy(1600-2100)
Prescription isodose line:79%(68-90%)Dmax:2580cGyFractions:1 to 4
Angiographic outcome:significant AVM reduction in all patients >1yr post SRS
6 of 19 patients obliterateNo angio done in 5 patientsClinical outcome:no further hemorrhages
3 PATIENTS28 YRS OLD LADY EMBOLISATION DONE TWICE PRESENTED WITH SEVERE PAIN IN THE POPLITEAL FOSSA AND CALF REGION
56 YEARS OLD LADY WITH SUDDEN ONSET OF MYELOPATHY
BOTH THE PATIENTS RESPONDED WELL25 yr old young man, repeated embolisations done,had no improvement
Current prescription dose to nidus is 2000 cGy in 2 sessions to larger lesions & 16-18 Gy for small (<0.7 cc) AVM
radiosurgery is a reasonable option in most type II spinal cord AVMs
Gerszten et al., Radiosurgery for spinal metastases: clinical experience in 500 cases from a single institution Volume 32,
Number 2, pp 193–199, 2007
500 cases of spinal metastases treated by CyberKnife® Radiosurgery at
the University of Pittsburgh
73 cervical, 212 thoracic, 112 lumbar, and 103 sacral lesions
Long-term pain improvement occurred in 290 of 336 cases (86%)
Long-term tumor control in 90% of lesions treated with radiosurgery as a primary treatment modality
Long-term tumor control in 88% of lesions that failed other therapies
Stereotactic radiosurgery is not a substitute to surgery but an alternative when indicated
SBRT is becoming a component in the multidisciplinary treatment of Cancer
In selected cases, SBRT may prove to be a curative modality of treatment in early cancers