IGRT RoboticaG.Beltramo

Centro Diagnostico Italiano

Varese 13 Giugno 2009

Image-Guided Radiation Therapy“Any use of imaging within the radiation

treatment room, to improve the precisionof radiation-therapy delivery”

“Use of any planar imaging, volumetricimaging, or volumetric ciné imaging, markerlocalization, marker tracking, patient surface

imaging, patient surface tracking to improve the precision of radiation therapy delivery.”

“IGRT is the process of in-room imaging that guides

the radiation delivery.”

Focus: Image guided RT Intervention

Three essential steps:

Acquire an image

• Acquire the positional information of the target, target surrogates, or avoidance structures

Obtain “target” registration error

• Image registration• Deviations from the original plan

Perform an intervention

• Correction strategies– Inter fraction/intra fraction, online/offline etc.

Advances in radiation technology

Stereotactic Radiosurgery System CyberKnife®

In 1991 Jonh Adler, an american neurosurgeon, develop a delivering stereotactic radiosurgery system without the need for

rigid immobilization

CyberKnife® Robotic Radiosurgery

• Non-coplanar treatment delivery

• Total of more than 1500 different beams

• Delivery of 150 to 200 uniquely angled beams per fraction

Image courtesy of Georgetown University Hospital

Need X ray vision!

• The target volume is located on X rays (orthogonal or stereoscopic) with fiducial markers or without them (if the target volume can be seen on X rays)• The images are to be fused and registered with the pretreatment DRR’s• The required shifts are calculated using customized software.• Shifts are made

Dx X-Ray Sources

Amorphous Silicon Detectors

Cyberknife (CK) therapy. CK (Accuray, Inc., Sunnyvale, California) is an image guided, frameless, radiotherapy device with a compact linear accelerator installed on an industrial-derived robotic arm, The intelligent arm has the capability of rotating around 6 axes with millimetric accuracy allowing a stereotactic radiosurgery (SRS) with high radiation doses to relatively small lesions. The treatment unit can verify target position with a real-time tracking during radiation delivery using two kV X-ray sources mounted on the ceiling and two amorphous-silicon image detectors mounted on the floor on either side of the patient in an orthogonal geometry to detect bony landmarks or fiducial markers within or near the target. The targeting system continuously acquires radiographs that are compared with the digitally reconstructed radiographs (DRR) derived from the treatment planning CT scans to update the changes in target position which are compensated by adjusting the aim of the robotic arm [ ].

Stereotactic Radiosurgery System CyberKnife®

Flowchart of the patient set up and delivery process in Cyberknife treatment

Cyberknife data acquisition

Image guidance

Stereographic X-ray images are compared with DRRs or fiducial positions

Robot corrects after each stereographic X-ray image acquisition

Robot can correct:± 10 mm all components± 1º roll± 1º pitch± 3º yaw

Planar X Rays (2D+) Advantages

– Fast image acquisition (single or fluoroscopic modes)– High temporal resolution– Tracking– Beam by beam correction– Motion management

Disadvantages

– Use of target surrogates (in most situations)– Obstructions in image viewing angles (anatomies or couch support in the beam path)– Not easy to reconstruct 3D dose distributions

“On-line Correction”Analysis of images and/or related data for potential corrections of the

delivery of the current fraction (i.e. analysis performed while the patient is still on the treatment couch).

Y

X-ray source

B

Pitch

Image A Image B

X-ray source

A

Camera A

Camera B

Verification of treatment accuracy

Skull may be good surrogate for brain

• Bone or marker??? spine bone poor surrogate for extracranial cancer

Verification of treatment accuracy

Verification of treatment accuracy

Accuracy of radiotherapy delivery depends on the visualisation of implanted gold fiducials at the time of treatment and comparison with references images obteined during treatment planning, . The advantage of Cyberknife tracking sistem is to verify in every step of treatment the real position of neoplstic target and the possibility to adjust the aim of robotic arm if the target position change during radiotherapy treatment

Total error in patient pose is dependent on the number of fiducials being tracked

3 fiducials significant improvement in targeting accuracy

> 6 fiducials adds little more improvement

Error in translations unaffected by spacing

Error in rotation is 50% by doubling the distance between fiducials

0

0.1

0.2

0.3

0.4

0.5

2 3 4 5 6number of fiducials

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Accuracy of fiducial targetting

Rigid body constraint

Distances between like fiducials compared

Histogram of prostate volume as a function of time duration and shift

Accuracy of fiducial targetting

Percentage of data set of having a movement as a

function of time

Rigid body error curve of three fiducials for four rappresentative

patients

Inter-fractional motion of the prostate during hypofractionated

radiotherapy

CDI Cyberknife experience

Real Time Imaging

Imaging with a temporal resolution that’ssufficient to capture the trajectory of a

movingor changing subject. Real time IGRT

correctionrefers to frequent imaging while the

treatment isbeing delivered, with repositioning based on

that imaging.real-time monitoring of any parameter must be fast enough to modify the treatment in

order to account for the impact of that parameter on treatment.

State of the art in room techniques for respiratory motion

managementTechnologies available

• Optical• MV/EPI• kV X ray• kV/MV/Optical• 4D CBCT/CT• Electromagnetic• Ultrasound• MRI

Respiratory Guided Radiation Therapy

moving the treatment beam as the target moves

Infrared LED-camera system records the respiration cycle

Real time

Motion management methods

CyberKnife® Robotic Radiosurgery

• Accuracy– Total targeting accuracy • Targets not affected by

respiration: 0.5 millimeter**• Targets that move with

respiration: 0.7 millimeter***– Targeting accuracy sustained

throughout the treatment

** Muacevic, A., Staehler, M., Drexler, C., Wowra, B., Reiser, M. and Tonn, J. Technical description, phantom accuracy and clinical feasibility for fiducial-free frameless real-time image-guided spinal radiosurgery. J Neurosurgery Spine. Xsight accuracy specification of .95 mm.

*** Dieterich S, Taylor D, Chuang C, Wong K, Tang J, Kilby W, Main W. The CyberKnife Synchrony Respiratory Tracking System: Evaluation of Systematic Targeting Uncertainty. Synchrony clinical accuracy specification of 1.5 mm for moving targets

* Kuka KR240-2 Specification 04.2004.05

• Individually fitted vacuum pillow

• Device for diaphragm compression (breathing tumor movements >10 mm at

fluoroscopy)

• Laser system for tattoos

Patient fixation - Stereotactic Elekta® Body Frame

Methods to avoid geographic miss

- ITV (abd compression), breath hold (ABC),

gating, and tracking

Cyberknife Radiosurgery : clinical rationale

Take Home Messages(Target Delineation)

• With robotic IGRT, treatment precision may be improved:

More accurate contours are REQUIRED

• Inaccurate contours could introduce unexpected target miss or increased toxicities

Day 0: fiducial insertion

Day 7: treatment planning TC. fiducial migration Day 10:

missing

Use For Tracking

Cannot be extracted Migration Obscured

Inaccurate target delineation

IMAGE FUSION TC-RM

Clinical use of this tecnique for treatment planning

has resulted in improvements in localization of treatment volumes and critical structures in the

brainKessler M.L.1991 Lattanzi J.P.1997

Use CT for geometric accuracyUse RM for target delineation

Image guidance facilitates targetting

TC-MRI image Fusion

MRI for Target Delineation Advantages

• Superior soft tissue image quality• For some tumors - greater sensitivity• Greater accuracy - delineation of some normal tissues• Functional information – normal tissues• Biological information – TME, blood flow, hypoxia• No radiation dose

Disadvantages

• Lack of specificity for tumor vs. other pathological states• Multiple effects that can lead to image distortion• Does not provide relative radiation attenuation• Requires fusion of grayscale images with CT dataset• Motion artifact• Cost

3D CRT and IMRT aim to achieve better locoregional control and improve survival by radiation dose escalation, but such techniques demand more accurate localization of tumor and surrounding normal tissues

Imaging in Target Delineation

Use of PET imaging to reduce interobserver

variations in contouring

STEENBAKKERS et al., IJROBP, Vol64, pp435, 2006

PET in Target Definition

Do SUVs mean anything?

Uncertainties in Manual Volume Alignment

Differences in Image Interpretation

• Inter-observer variation

Contours may not be drawn perfectly One person’s alignment may not agree with another person’s judgment

• Impact of organ deformation

Imperfect alignment

SBRT theoretical basis

Operable lung cancer patients

Extent of resection impacts local control

(e.g., wedge vs. lobectomy – LCSG trial)Local control impacts survival

Goal with SBRT in inoperable patients should be very high local control until

proven otherwise

At treatment After 3 months After 12 months

Large Japanese Study (Onishi, 2007)

SBRT for early stage lung carcinoma

Indiana phase I trial

SBRT toxicity

Respect Normal Tissue Constraints

Respect Normal Tissue Constraints

Organ at risk dose coinstrain

12 months post SBRT

3 months post SBRT

6 months post SBRT

Respect Normal Tissue ConstraintsGRADE II

GRADE III

GRADE IV

Local Therapy and Image-Guidance

• Radiation therapy is a proven local therapy.

• Increased precision in therapy offers:– Reduce severity and risk of therapy-induced complications.– Increase both quality and probability of success.

• Further potential:– Broaden application of proven therapies.– Permit new therapies that are intolerant to geometricimprecision.

• Addressing geometric uncertainties may expose otherfactors determining outcome.

Not a single IGRT solution can correctall sources of uncertainties

Systematic Random

Inter-fractional Intra-fraction

Shape Variations Time Trends

The living patient and thedynamic treatment problem

What could possibly go wrong and how could that happen?

Inadequate implementation of IGRT technology for the treatment site

What effects would such a failure produce?

Suboptimal treatment Failure to control cancer Increased toxicities Waste of resources

Clinical benefit of image guided robotic radiotherapy

Stereotactic body radiotherapy (SBRT) is the Latest Generation of “Targeted “ therapies for

radiation