sbrt position monitoring with exactrac following...

Gundersen Lutheran Medical Center, Inc. | Gundersen Clinic, Ltd.

SBRT Position Monitoring with

ExacTrac Following CBCT

John Wochos, MS, DABR

Casey Abing, MS, DABR

Gundersen Health System

La Crosse, WI


Equipment at Gundersen

• GE Lightspeed CT Sim

• RPM gating system

• Varian Clinac 21EX

• BrainLAB ExacTrac System

• BodyFix immobilization system

• Mosaiq R&V

• 4DTC

• On-Board Imaging system


SBRT Workflow

1. CT Simulation (gated vs. no gating)

2. Planning (IMRT vs. non-IMRT)

3. Gantry/Couch clearance check

4. Patient specific QA

5. Treatment


CT Simulation

• Arms overhead

• No respiratory coaching

• Rarely use abdominal compression

• Phase-based gated CT scan (RPM system)

• Physician and physicist review gated scan

together to determine efficacy

• Roughly 30% of patients are gated for

treatment


Planning 1• Non-gated treatement: planning is done on the 0% – 90% Average

Intensity Projection (Ave-IP)

• Gated treatment: the Ave-IP of the desired phases for gating (e.g. 30% - 60%)

• Contouring is assisted using the Maximum Intensity Projection (MIP) CT

• Roughly 33% are treated “IMRT” (1-3 segments per beam, minimize interplay effect)

• Use 12-15 non-coplanar beams to conform to RTOG 0813 (couch kicks at 330°, 30°, and 90°)

• Prefer Pinnacle CC algorithm over Eclipse AAA


Planning 2 – Example 1

– 13 field, non-coplanar, step and shoot IMRT, 21 total segments, non-gated, 600 MU/min, thinner patient (i.e. ideal situation)

– Patient in/out time: 25-30 minutes• Setup: 5 minutes

• CBCT, review, kV orthogs: 8 minutes

• Treatment Delivery: 12 minutes


Planning 3 – Example 2

– 15 field, non-coplanar, step and shoot IMRT, 25 total segments, gated 30%-60% phases, 600 MU/min, (i.e. worst situation)

– Patient in/out time: 50-60 minutes• Setup: 5 minutes

• CBCT, review, kV orthogs: 15 minutes

• Treatment Delivery: 34 minutes


ExacTrac System Background 1

Dual floor-mounted kV x-ray tubes

Ceiling-mounted

aSi flat panel

detectors

Video and IR camera

Orthogonal/oblique images at isocenter


ExacTrac System Background 2

• Advantages

– Fast acquisition

– Accurate and precise with respect to BONY landmarks in 6 degrees of freedom

– Auto-fusion very good, no manual adjustment needed

– Independent of the treatment machine

– Low patient dose

• Main disadvantage

– No direct soft tissue matching

– Images are not intuitive to interpret (trust the system)


OBI CBCT Background

Click Here for OBI Demo

• Advantages• High contrast images (especially for lung)

• 3D images

• Auto or manual fusion options

• Full window/level ranges

• Images are very easy to interpret

• Disadvantages• SLOW acquisition

• Data transfer to Mosaiq R&V

• Increased patient dose


SBRT Treatment Workflow

• Initial patient setup

• CBCT (fuse to bone, shift to tumor using ITV from

Ave-IP 0 – 90%)

• kV orthogonal pair (double checks CBCT)

• Initial ExacTrac sets a baseline (no shifts applied)

• Follow-up ExacTrac done every 2 – 3 fields

• Re-CBCT if follow-up ExacTrac differs from

baseline ExacTrac by more than 2mm


Data 1Patient: Posterior Left Lower Lobe Lung

Dose: 1000cGy x 5 fractions

ITV => PTV margin: 10mm sup/inf and 5mm radially

Treatment fields: 12 field non-coplanar 3D conformal

Gating: 30%-70% phases

Treatment time: setup (5 mins), IGRT (12 mins), beam on (20 mins)

In/Out time = around 45 mins

Baseline – First Verification Baseline – Second Verification Baseline – Third Verification Baseline – Fourth Verification

Fraction Vert Long Lat Vector Vert Long Lat Vector Vert Long Lat Vector Vert Long Lat Vector

1 0.23 -0.11 0.22 0.34 0.48 -0.10 0.37 0.61 0.45 0.26 0.18 0.55 - - - -

2 -0.02 -0.15 -0.26 0.30 -0.16 0.08 0.05 0.19 0.22 -0.14 -0.40 0.48 0.37 -0.33 -0.37 0.62

3 0.02 0.08 0.14 0.16 0.10 -0.33 0.39 0.52 0.09 -0.48 -0.15 0.51 - - - -

4 -0.07 -0.14 -0.47 0.50 -0.01 -0.20 -0.25 0.32 -0.01 -0.51 -0.06 0.51 0.06 -0.67 -0.06 0.68

Max

Deviation0.23 0.08 0.22 0.50 0.48 0.08 0.39 0.61 0.45 0.26 0.18 0.55 0.37 -0.33 -0.06 0.68


Data 2Patient: Left Lower Lobe Lung

Dose: 1000cGy x 5 fractions

ITV => PTV margin: 10mm sup/inf and 5mm radially

Treatment fields: 12 field non-coplanar 3D conformal

Gating: 30%-60% phases

Treatment time: setup (5 mins), IGRT (15-20 mins), beam on (25-30 mins)

In/Out time = around 50 mins

Baseline – First Verification Baseline – Second Verification Baseline – Third Verification Baseline – Fourth Verification

Fraction Vert Long Lat Vector Vert Long Lat Vector Vert Long Lat Vector Vert Long Lat Vector

1 -0.10 -0.88 -0.24 0.92 0.29 -0.18 0.18 0.39 0.11 0.05 -0.52 0.53 - - - -

2 0.50 0.95 -0.80 1.34 0.00 4.04 -0.50 4.07 - - - - - - - -

2reCBCT -0.50 0.30 0.30 0.66 0.10 -0.80 1.00 1.28 - - - - - - - -

3 0.00 0.80 0.04 0.80 0.70 0.70 0.32 1.04 0.60 1.20 1.02 1.69 0.50 1.30 1.32 1.92

4 0.00 0.10 -0.20 0.22 -0.77 0.60 -0.90 1.33 - - - - - - - -

5 0.34 0.85 -0.40 1.00 0.85 0.70 -0.10 1.11 1.76 1.07 -0.77 2.20 1.26 1.17 -1.52 2.29

Max

Deviation0.50 0.95 0.30 1.34 0.85 4.04 1.00 4.07 1.76 1.20 1.02 2.20 1.26 1.30 1.32 2.29


Conclusion

• The ExacTrac relative positioning workflow

gives us fast, accurate and precise information

regarding intra-fraction motion

• With four patients and eighteen fractions,

only one patient needed a new CBCT, indicates

our immobilization system is working well


Winter is Coming


2013 AAPM Summer School

• Quality & Safety in Radiotherapy

• How to Apply at Gundersen’s Radiation

Oncology Department without Physicists

becoming Safety Engineers….


Gundersen Safety Initiative

• First; attempt to make better use of Incident

data

• Have been recording Incidents (Major, Minor

and in-between) for >15 years.

• Early on we found trends and made system

changes

• Over the past 5 years few obvious trends or

“system issues”


Incident Data

• Re-encourage staff to report

• Determine, from AAPM recommendations the

“Causality Classifications” for each incident

• Try to determine the Root Cause of each

Incident


Avoid the Next Major Incident

• How to determine what it will be?

• Survey ALL staff in the department

• Request feedback on 2 or 3 items

• Either most likely or most risky thing that is

occurring from your perspective

• This can also achieve staff involvement in a

Safety Culture. Encouraged input from

everyone.


Avoiding Incidents, Results

• Over 90% of staff replied

• Over 50% of staff have volunteered to be

involved in follow-up.

• Staff at ALL levels will be involved in follow-up

(MAs, RNs, PA, Physics, Dosimetry, MD,

Therapists).


Data

Item Frequency Item Frequency

Emergency Response (Code) 1 Overall communication 1

Incorrect patient 2 Wrong site/ dose SRS 1

Patient slipping, falling, transfer 2 Wrong site/ dose LDR 1

Confientiality 1 HDR Calibration 1

HDR Source gets stuck 1 Friday BIDs inconsistancy 1

HDR catheter mis-measure 1 Wrong site 1

Late , hurried dosimetry 3 Linac Miscalibration 2

Wrong Dose delivered 0 Correct bolus informatioin Dosim to treat 1

Short staff (MAs) 2 CT contrast reaction 1

ExacTrac transfer Room to room 1 Communication (human & computer) 1

Rm 1 no bar code (gate, bolus,couch angle) 7 Lifting patient On/Off table 1

Staff hour reductions 1 Bathroon doors, no auto openers 1

Technology upgrades 6 Missing / delayed boost dosimetry 1

Advanced Care Planning involvement 1 Gating incorrect 2

Patient mis identified (name only no ID#) 1 Changing MD contours or beams in dosim 1

Incomplete/Excessive scheduling on orders 2 Wrong CT coordinates Rm 1 4


Categorized Data

Linac Technical Communication

Item Frequency Item Frequency

Rm 1 no bar code (gate, bolus,couch angle) 7 Incorrect patient (or misidentify) 3

Technology upgrades 6 Confidentiality 1

Wrong CT coordinates Rm 1 4 Overall communication 1

Gating incorrect 2 Friday BIDs inconsistency 1

Linac Miscalibration 2 Communication (human & computer) 1

Correct bolus informatioin Dosim to treat 1

ExacTrac transfer Room to room 1 Non-radiation safety

Item Frequency

Brachytherapy Patient slipping, falling, transfer 3

HDR Source gets stuck 1 Short staff (MAs) 2

HDR catheter mis-measure 1 Incomplete/Excessive scheduling on orders 2

HDR Calibration 1 Emergency Response (Code) 1

Wrong site/ dose LDR 1 Staff hour reductions 1

Advanced Care Planning involvement 1

Dosimetry CT contrast reaction 1

Item Frequency Bathroom doors, no auto opener 1

Late , hurried dosimetry 3

Wrong Dose delivered 1

Changing MD contours or beams in dosim 1

Wrong site/ dose SRS 1

Wrong site 1

Missed/ delayed boost 1


Failure Mode & Effects Analysis

• Occurrence = Likelihood event will occur, to

the undesired result: 1=Remote/ 10=For sure

• Severity: 1=No effect, 2=Minor, 7=serious,

10=death

• Detectability: 1= always, 10=Never


Evaluation of Data

Linac Technical Occurance OxSxD

Item Frequency Likelihood Severity DetectabilityRiskPriority

Number

Rm 1 no bar code (gate, bolus,couch angle) 7

Technology upgrades 6 7 8 4 224

Wrong CT coordinates Rm 1 4 3 7 2 42

Gating incorrect 2 3 6 7 126

Linac Miscalibration 2 2 10 2 40

Correct bolus informatioin Dosim to treat 1 5 3 9 135

ExacTrac transfer Room to room 1

Brachytherapy

HDR Source gets stuck 1 2 9 2 36

HDR catheter mis-measure 1 3 9 6 162

HDR Calibration 1 2 9 2 36

Wrong site/ dose LDR 1 2 7 2 28

Dosimetry

Item Frequency

Late , hurried dosimetry 3 9 9 5 405

Wrong Dose delivered 1 3 8 6 144

Changing MD contours or beams in dosim 1 3 4 5 60

Wrong site/ dose SRS 1 3 9 5 135

Wrong site 1 3 9 4 108

Missed/ delayed boost 1 2 2 2 8


Safety Initiative, Conclusions

• None to date

• We’ve had an explosion in workload; what

happens to safety when extremely busy?

• Survey � same events, just more of them or

higher probability

• If this initiative is successful, we will never

know because the major event will not

happen!


Thank you

• Questions

• Comments

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