Hit or Miss: Is there a role for CT/MRI fusion in Sarcoma radiotherapy planning?

Paris-Ann Gfeller

B.C. Cancer Agency, Vancouver, Canada Musculoskeletal Tumour Group

C. Candish, K. Goddard, C. Grafton, L. Weir

Outline

o Background

o Study Design

o Results

o Conclusions

BackgroundSarcoma Radiotherapy Planning

o The delineation of tumor from normal tissues is critical to the radiotherapy planning process

o In Sarcoma treatment planning, improper delineation of tumour can lead to:

Over-treatment of normal tissues o Severe late effects of

treatment(fibrosis, fracture, edema)

Under-treatment of tumouro Tumour recurrence

BackgroundSarcoma Radiotherapy Planning

o Appropriate imaging is essential to properly delineate tumour volumes

o Majority of current radiotherapy planning systems are CT based

o With CT images alone it can be difficult to differentiate between tumor and normal tissue

o Sarcomas are routinely imaged using MRIo MRI correlates with tumour extent and invasion into local structureso MRI shows peritumoral edema, which is included as part of target

volume

BackgroundCT vs. MRI

CT MRI

Tumour is better defined by MRI compared to CT

BackgroundHow Can We Combine CT and MRI?

By co-registering (fusing) CT and MRI images, Radiation Oncologists can contour on CT and MRI simultaneously, using imaging information from both modalities

CT MRI

BackgroundHow is Fusion Done?

CT MRI-Fusion

BackgroundCT/MRI Fusion for Sarcomas?

There are no published studies describing the use of CT/MRIFusion for sarcoma treatment

o CT/MRI Fusion studies in other tumor sites have shown:

o Improved tumor delineation with fusion o More accurate representation of gross disease

o Decreased interobserver, intraobserver variation with fusion o More reproducible

o Is there a benefit for CT/MRI fusion in sarcoma radiotherapy planning?

Study Questions?

1. Is CT-MRI Fusion useful in sarcoma planning?o Does Fusion alter the tumour volumes? o Does Fusion improve consistency between observers

(interobserver variation)? o Does Fusion improve consistency within observers

(intraobserver variation)?

2. Is CT/MRI fusion felt to be valuable to the planning process? o Radiation Oncologists opiniono Radiation Therapists opinion

Study Design

In 2004 a BCCA protocol was developed for fusion

sarcoma patientso Coordination of planning CT and MRI on the same

day, in treatment position, with an immobilization device

o “Best” MRI image series selected in consult with radiology and fused with a planning CT

Study Design

o 19 patients were planned and treated from May 2004 to February 2005 at Vancouver Cancer Centre (BCCA) with the CT-MRI fusion protocol

o Identified all patients who had been treated according to protocol

o Excluded patients who had received chemotherapy or surgery prior to radiation planning

o Excluded tumours located in the thorax or head and neck

o 9 patients met study criteriao 6 patients treated preoperatively, 3 patients had

radiotherapy as definitive treatmento 5 MFH, 3 Fibromatosis, 1 Liposarcoma

Study Design

o Original non-contrast planning CT images and MRI images retrieved and then co-registered to produce CT/MRI fusion images

o 2 image sets for each patient createdo CT image seto CT/MRI fusion image set

Study Design

3 Radiation Oncologists (RO’s)

9 CT Image Sets9 Patient Summaries

Contour tumour volumesComplete Survey

9 Fusion Image Sets, 9 Patient Summaries

Contour tumour volumesComplete Survey

54 Image Sets

Volumes Analyzed for:

Difference in Mean Volumes

Max/Min Ratio, X/Y/Z

Observers repeated contours on CT and Fusion for Intraobserver Δ

Minimum 2 week delay between contouring on image sets

RESULTS

ResultsMean Contoured Tumour Volume By Patient

0200400600800

100012001400160018002000

1 2 3 4 5 6 7 8 9

Patient Number

Mean Volume (cc)

CT Fusion

CT volumes were 20% larger then fusion volumes

ResultsContoured Tumour Volumes

Oncologists included more NORMAL TISSUE if unsureof volume on CT vs. MRI

o This accounted for larger overall CT volumes

CT Fusion

ResultsContoured Tumour Volumes

CT contours not always inclusive of MRI signal changes

oGROSS TUMOUR EXCLUDED

CT Fusion

Interobserver VariationMaximum Variation Ratio

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9

Patient Number

Max/Min Volume Ratio

CT Fusion

Compare Max/Min Contoured Volume for each patient between observers

o More Interobserver Variation with CT

o Volumes contoured with Fusion more consistent between observers

CT Fusion

Interobserver VariationMaximum Variation Ratio

Intraobserver VariationMaximum Variation Ratio

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1 2 3 4 5 6 7 8 9

Patient number

max/min ratio

ct fuse

Compare Max/Min Contoured Volume for each patient within observers

oMore Intraobserver Variation with CT

o Contoured Tumour Volumes (GTV) o Mean CT volumes by pt were larger then Fusion volumes o Mean CT gross tumour volumes for each patient were 1.2 times

larger (range 0.90-1.56) then CT/MRI fusion images o p=0.04

o Interobserver Variation (Maximum Variation Ratio) o CT 3.72 (range 1.19- 9.0)o Fusion 1.72 (range 1.16-3.07)o Less interobserver variation with fusion p=0.001

o Intraobserver Variation (Maximum Variation Ratio) o CT 1.41 (range 1.03-1.72)o Fusion 1.10 (range 1.01-1.27)o Less intraobserver variation with fusion p=0.02

ResultsContoured Tumour Volumes

ResultsSurvey

o 10 question survey completed by Radiation Oncologists and Radiation Therapists involved in sarcoma planning after completing planning

o Radiation Oncologists unanimously felt better able to delineate tumour from normal tissue with fusion

o Radiation therapists felt fusion aided in their ability to prepare images (contour critical structures) in preparation for planning by Radiation Oncologists

Conclusions A Role for Fusion in Sarcoma Planning?

o One of first studies to formally evaluate use fusion for planning sarcomas

o Results justify use of fusion o Fusion allows Radiation Oncologists to define smaller more

accurate volumes which may:o decrease dose to normal tissueso Improve tumour coverage

o Fusion increases consistency and reproducibility of treatment planning

Results show the optimal modality for planningsarcoma is CT-MRI Fusion to ensure gross diseaseappropriately represented

Thank you

o CTOS Abstract Review Committee

o BCCA Musculoskeletal Tumour Group

o Dr. C. Candisho Dr. K. Goddardo Dr. C. Grafton o Dr. L. Weir

o Dr. C. Keogh (Radiology)o C. Marlowe, K. Dahle, C. Mengerink

(Radiation Therapy)o V. Morovan (Statistics)

“Imaging Matters”

Questions?

Supplementary Slides

ResultsCT with Bowel Contrast

CT with Contrast MRI

ResultsCT with IV Contrast

CT with Contrast MRI

ResultsImaging and Registration

    Registration Error

Patient #  MRI Type avg error (cm) max error (cm)

1 T2FS 0.15 0.33

2 STIR 0.34 0.41

3 T1FS 0.28 0.61

4 T2FS 0.26 0.38

5 T2FS 0.31 0.63

6 T2FS 0.4 0.77

7 T2FS 0.57 0.79

8 T2FS 0.16 0.23

9 T2FS 0.28 0.45

    0.305556 0.511111

MRI slices 5mm

ResultsContoured Tumour Volumes

CT Fuse

ResultsContoured Tumour Volumes PTV’s

CT Fuse

Results Underestimate Tumour Extent

ResultsContoured Tumour Volumes

ResultsGross Tumour Volumes by Observer

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

MRI Volume (cc)

CT Volume (cc)

ResultsGross Tumour Volume By Patient

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9

Patient Number

Volume cc

doc1 ct doc2 ct doc3 ct

doc1 fuse doc2 fuse doc3 fuse

ResultsMean Gross Tumour Volume By Patient

o CT volumes 1.2 times larger then fusion, p=0.04

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9

Patient Number

Volume cc

CT Fusion

ResultsMean PTV By Patient

0

1000

2000

3000

4000

5000

6000

1 2 3 4 5 6 7 8 9

Patient Number

Volume cc

CT Fuse

ResultsMeasuring Variation

ResultsMEAN X,Y,Z Variation

  CT   Fusion  

  avg SD avg SD

med 3.74 1.12 3.63 0.4

lat -4.44 1.63 -4.28 0.4

     

ant 4.93 0.7 4.3 0.4

post -3.91 1.4 -3.78 0.6

     

sup 7.43 1.8 6.57 0.8

inf -7 2.36 -6.28 0.8

Standard Deviation smaller for fusion all directions

All dimensions smaller for Fusion

(sup/inf most significant)

ResultsVariation Superior to Inferior

-15

-10

-5

0

5

10

15

20

0 5 10 15 20 25

Series2

Series3

Series4

Series5

Series6

Series7

Series8

Series9

Series10

Series11

Series12

Series13

Series14

Series15

Series16

Series17

Series18

Series19

Series20

Series21

Series22

ResultsMedial and Lateral Variation

ct ct   fuse fuse

med lat   med lat

6 -5.5   5 -4

1 -1.5   1 -2

3 -2.67   3 -2

3.333 -6.33   5.2 -5

2 -2.67   0 -3.167

1.333 -1.83   1.3 -3

6 -6   5.5 -7.333

5 -5.5   4.7 -5

6 -8   7 -7

3.741 -4.44   3.6 -4.278

ResultsCompletion Survey

Survey completed for each image set at completion of contouring (N=88)Linear Analog Rating Scale

Rate the general quality of this CT (fusion) image set? (1 – poor, 5-meets expectations, 10 – exceeds expectations)

o CT score 4.9, Fusion 6.7o Both image sets were “acceptable” for contouring

Rate the quality of this CT (fusion) image set for delineating: (1- can not delineate to 10 –exceeds expectations)

a. Tumor volumeo CT 4.0, Fusion 7.8

b. Critical Structures o CT 4.2, Fusion 7.4

Indicates Subjectively “Better" Delineation of

Tumour and Critical Structures with Fusion

ResultsRadiation Oncologists Completion Survey

Using a linear analog scale (poor to exceeds expectations)

rate the quality of this CT (fusion) image set for delineating:

Tumour Volumes

o CT 4.0, Fusion 7.8

1 2 3 4 5 6 7 8 9 10

1

Fuse

CT

1 2 3 4 5 6 7 8 9 10

1

Fuse

CT

Normal Tissues CT 4.2, Fusion 7.4

Improved Delineation of Tumour and Normal Structures with Fusion

poor meets expectations exceeds poor meets expectations exceeds

ResultsRadiation Therapists Opinions

8 question survey for Radiation therapists (n=4) involved in sarcoma fusions

1. Average time for fusiono 35.5 minutes

2. Usefulness of Fusion for delineating normal structureso Extremely useful

3. Difficulty of Performing Fusions compared to other siteso Slightly more difficult, (extremities the most difficult)

4. Important factors in image fusiono Tumour location, MRI quality, time availableo IMMOBILIZATION and Position

ConclusionsA Role for Fusion in Sarcoma Planning?

o CT/MRI fusion is valuable to the planning process for sarcoma

o Contoured Tumour Volumeso More normal tissue included in the target volumes with CTo Disease excluded on CT

o Volume Variation o More consistency in contours with Fusion

o Completion Survey o Radiation Oncologists and Therapists felt fusion was

valuable