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

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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

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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