Initial Clinical Experience with 3D Surface Image Guidance

Amanda Havnen-Smith, Ph.D.

Minneapolis Radiation Oncology

Ridges Radiation Therapy Center

Burnsville, MN

April 20th, 2012

OUTLINE

• Description of 3D Optical Tracking System and Purpose

• Use of the System and the Workflow

• Strengths and Weaknesses of the System

• TG 147 Recommended Quality Assurance

Non-funded

research

collaboration

Can be used for

patient set-up and

surveillance

3-D

Non-Invasive

Non-Ionizing

Why use 3D surface image guidance?

Purpose of Surface Image Guidance

Inter-Fraction

Give consistency with day-to-day patient setup

Intra-Fraction

Capability to pause treatment if patient moves out of

acceptable position

Capability to gate the beam for motion management

The goal is to reduce two types of uncertainty in external

beam RT

As EBRT

treatments

become more

conformal,

patient

positioning and

motion

management

become even

more critical!

Small errors can be “gross” errors!

Cameras project a red speckle pattern on the surface of the patient, and determine where the patient’s surface is in space.

Technology

Stereoscopic System

3D Surface Information from Image Pair

1) Known Feature Extraction

- Structured light projection (speckle pattern)

2) Locate corresponding feature in 2nd image

3) Compute 3D coords of features using triangulation

Camera Pod

Software calculates the position of each point along

the CT surface with respect to the isocenter

Compares the position of all points on the acquired

surface (in the Region of Interest) with respect to the

planned isocenter

Does not directly compare the acquired surface to the

planned surface

Does not directly account for deformation

Do have the option of adding additional ROIs, and

you may use centroid method for these

- This method compares the weighted centroid of the

actual surface to that of the reference surface

Strongly recommend using centroid option for objects

far from isocenter

-For example on a breast patient: chin ROI, arm ROI

Strongly recommend not to use the centroid option for

primary ROI set-up, system not optimized for this

Planning CT Surface (body contour)

Ideally our preference

Large amount of image data

Frame rate is slower

Surface can have features not present at treatment

Recorded surface in treatment position

Faster frame rate for real-time shifts, beam holds

Relationship to CT surface is not known

What do we compare the treatment position to?

Wires, Fiducials, Artifacts, etc.

Requires attention to the body contour?

WORKFLOW System isocenter “calibrated” by physics once a month

Constancy of iso checked daily by therapists

Dosimetrist/Physicist exports data and therapist

imports into AlignRT software:

Structure Data (dicom RTStructure file)

- From this only the Body contour is used

Treatment plan for each isocenter (dicom RTPlan

file)

- Only need to export a single plan if plans have

+ Same CT image set

+ Same isocenter

Imported Surface

& Isocenter

ROIs: Functionality largely dependent on ROIs

Manufacturer recommends:

Not too big – T.M.I.!

Not too small – Not enough info to localize!

Works best with well-defined features Does not work as well with fleshy mobile features (large breasts) or highly symmetric features (expanders)

It is recommended to include:

Breast tissue (if not too pendulous or symmetric)

Some axilla/arm

Some lower neck/SCLAV

Part of

lateral chest

wall

Patient Setup

Line up patient using marks, lasers, SSDs

Begin monitoring , use “real-time deltas” to move patient into correct

position

Real-time shifts shown for 3 translations,

3 rotations

• w/in 3 mm and 30 (default tolerance)

Then initiate treatment

Can record treatment surface

Can generate a report showing the offsets at any time

Treatment Monitoring

If patient moves significantly, could pause tx

and re-align to plan

- Can be helpful for non-compliant

patients, can see motion on camera,

but did they move back??

If bolus patient, we apply it, then capture new

image to monitor motion

Motion management tool

Deep Inspiration Breath Hold (DIBH)

Technique

Goal to reduce risk of cardiac toxicity by increasing

the distance between heart and breast.

Allows IMRT treatment of breast/chest wall

DIBH Workflow

Acquire free-breathing CT and DIBH CT w/o change

in position between scans

Treatment plan developed on DIBH CT (can plan a

back-up free breathing plan in case system goes down)

Both Body surfaces and DIBH plan exported Free-breathe surface is used for rough patient positioning

DIBH surface is used to guide patient into position for gated treatment

DIBH Workflow

Verification simulation performed on the linac prior

to initiating treatment Test patient compliance with gated technique

Verify ROIs drawn are appropriate for monitoring with gantry angles

Patient aligned using lasers, marks, SSDs then real-

time deltas using free-breathing surface

The surface is then changed to the DIBH surface,

monitoring of real-time deltas is initiated and the patient

is coached to take a deep breath in until all parameters

are within tolerance

DIBH Workflow

When the patient is at full inspiration Lateral position can be adjusted by moving the table

Vertical position is adjusted by asking the patient to breathe more/less

Longitudinal position typically also controlled by breath size

- Can fine-tune with couch if necessary

SSDs/Port films/KV images all acquired during

breath hold

There is a “Coaching” display option that is helpful

for therapists Displays only Vertical position parameter

Bar moves up and down like chest wall, turns from green to yellow

when all parameters within tolerance (gating window)

DIBH Technique

Coaching view with real-time deltas

Strengths and Weaknesses

Strengths:

Non-ionizing

Therapists find it to be very useful for setup

Faster

More efficient, fewer re-ports

Intra-fraction monitoring capability

Motion management option

Can capture charges for image guidance

Setup

Monitoring

Strengths and Weaknesses

Weaknesses:

ROI selection is very tricky, learning curve

Position readouts can become unreliable when

gantry interferes in camera line of sight

- Especially problematic in gating patients

Learning curve for developing troubleshooting

techniques

The system is very “Black Box”, requires

physicist to develop a thorough QA procedure

Strengths and Weaknesses

Black Box: Manufacturer’s calibrations and

constancy checks give only RMS error

output

TG 147 Report on QA for non-radiographic

radiotherapy localization and positioning

systems has detailed recommendations

TG 147 QA

Thorough guidance on commissioning

Daily QA – Safety & Static Localization

Phantom positioned at isocenter and can track

movement to isocenter from offset

Accuracy should be w/in 2 mm

Monthly QA –

Safety: Gating terminates, Couch motion

Static Localization: Localization test based on

radiographic analysis (i.e. hidden target test)

Dynamic localization: Motion table or manual

couch motion of monthly phantom by known

distances

TG 147 QA

Annual QA -

Safety: Camera mounting secure

Integrity: Check camera settings

Stability: Drift Measurement (min 1 hr),

reproducibility of localization

Static localization: Full end-to-end testing,

translation and rotation correct w/in clinical range

Dynamic (for gating): Use of motion phantom

Data transfer functionality

Quality assurance for nonradiographic radiotherapy

localization and positioning systems: Report of Task

Group 147 Medical Physics, Vol 39, Issue 4

Thank You!!

Any Questions??