Title: Hit or Miss: Is there a role for CT/MRI fusion in Sarcoma radiotherapy planning?
1Hit or Miss Is there a role for CT/MRI fusion in
Sarcoma radiotherapy planning?
B.C. Cancer Agency, Vancouver, Canada
Musculoskeletal Tumour Group C. Candish, K.
Goddard, C. Grafton, L. Weir
2Outline
- Background
- Study Design
- Results
- Conclusions
3BackgroundSarcoma Radiotherapy Planning
- The delineation of tumor from normal tissues is
critical to the radiotherapy planning process - In Sarcoma treatment planning, improper
delineation of tumour can lead to - Over-treatment of normal tissues
- Severe late effects of treatment
- (fibrosis, fracture, edema)
- Under-treatment of tumour
- Tumour recurrence
4BackgroundSarcoma Radiotherapy Planning
- Appropriate imaging is essential to properly
delineate tumour volumes - Majority of current radiotherapy planning systems
are CT based - With CT images alone it can be difficult to
differentiate between tumor and normal tissue - Sarcomas are routinely imaged using MRI
- MRI correlates with tumour extent and invasion
into local structures - MRI shows peritumoral edema, which is included as
part of target volume
5BackgroundCT vs. MRI
Tumour is better defined by MRI compared to CT
MRI
CT
6BackgroundHow 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
MRI
CT
7BackgroundHow is Fusion Done?
CT
MRI-Fusion
8BackgroundCT/MRI Fusion for Sarcomas?
- There are no published studies describing the use
of CT/MRI - Fusion for sarcoma treatment
- CT/MRI Fusion studies in other tumor sites have
shown - Improved tumor delineation with fusion
- More accurate representation of gross disease
- Decreased interobserver, intraobserver variation
with fusion - More reproducible
- Is there a benefit for CT/MRI fusion in sarcoma
radiotherapy planning?
9Study Questions?
- Is CT-MRI Fusion useful in sarcoma planning?
- Does Fusion alter the tumour volumes?
- Does Fusion improve consistency between observers
(interobserver variation)? - Does Fusion improve consistency within observers
(intraobserver variation)? - Is CT/MRI fusion felt to be valuable to the
planning process? - Radiation Oncologists opinion
- Radiation Therapists opinion
10Study Design
- In 2004 a BCCA protocol was developed for fusion
- sarcoma patients
- Coordination of planning CT and MRI on the same
day, in treatment position, with an
immobilization device - Best MRI image series selected in consult with
radiology and fused with a planning CT
11Study Design
- 19 patients were planned and treated from May
2004 to February 2005 at Vancouver Cancer Centre
(BCCA) with the CT-MRI fusion protocol - Identified all patients who had been treated
according to protocol - Excluded patients who had received chemotherapy
or surgery prior to radiation planning - Excluded tumours located in the thorax or head
and neck - 9 patients met study criteria
- 6 patients treated preoperatively, 3 patients
had radiotherapy as definitive treatment - 5 MFH, 3 Fibromatosis, 1 Liposarcoma
12Study Design
- Original non-contrast planning CT images and
- MRI images retrieved and then co-registered to
produce CT/MRI fusion images - 2 image sets for each patient created
- CT image set
- CT/MRI fusion image set
13Study Design
3 Radiation Oncologists (ROs)
9 CT Image Sets 9 Patient Summaries Contour
tumour volumes Complete Survey
9 Fusion Image Sets, 9 Patient Summaries Contour
tumour volumes Complete 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 ? Minimum 2 week delay between
contouring on image sets
14RESULTS
15ResultsMean Contoured Tumour Volume By Patient
CT volumes were 20 larger then fusion volumes
16ResultsContoured Tumour Volumes
CT
Fusion
- Oncologists included more NORMAL TISSUE if unsure
- of volume on CT vs. MRI
- This accounted for larger overall CT volumes
17ResultsContoured Tumour Volumes
Fusion
CT
- CT contours not always inclusive of MRI signal
changes - GROSS TUMOUR EXCLUDED
18Interobserver VariationMaximum Variation Ratio
Compare Max/Min Contoured Volume for each patient
between observers
- More Interobserver Variation with CT
19Interobserver VariationMaximum Variation Ratio
CT
Fusion
- Volumes contoured with Fusion more consistent
between observers
20Intraobserver VariationMaximum Variation Ratio
Compare Max/Min Contoured Volume for each patient
within observers
- More Intraobserver Variation with CT
21ResultsContoured Tumour Volumes
- Contoured Tumour Volumes (GTV)
- Mean CT volumes by pt were larger then Fusion
volumes - Mean CT gross tumour volumes for each patient
were 1.2 times larger (range 0.90-1.56) then
CT/MRI fusion images - p0.04
- Interobserver Variation (Maximum Variation Ratio)
- CT 3.72 (range 1.19- 9.0)
- Fusion 1.72 (range 1.16-3.07)
- Less interobserver variation with fusion p0.001
- Intraobserver Variation (Maximum Variation Ratio)
- CT 1.41 (range 1.03-1.72)
- Fusion 1.10 (range 1.01-1.27)
- Less intraobserver variation with fusion p0.02
22ResultsSurvey
- 10 question survey completed by Radiation
Oncologists and Radiation Therapists involved in
sarcoma planning after completing planning - Radiation Oncologists unanimously felt better
able to delineate tumour from normal tissue with
fusion - Radiation therapists felt fusion aided in their
ability to prepare images (contour critical
structures) in preparation for planning by
Radiation Oncologists
23 Conclusions A Role for Fusion in Sarcoma
Planning?
- One of first studies to formally evaluate use
fusion for planning sarcomas - Results justify use of fusion
- Fusion allows Radiation Oncologists to define
smaller more accurate volumes which may - decrease dose to normal tissues
- Improve tumour coverage
- Fusion increases consistency and reproducibility
of treatment planning - Results show the optimal modality for planning
- sarcoma is CT-MRI Fusion to ensure gross disease
- appropriately represented
24Thank you
- CTOS Abstract Review Committee
- BCCA Musculoskeletal Tumour Group
- Dr. C. Candish
- Dr. K. Goddard
- Dr. C. Grafton
- Dr. L. Weir
- Dr. C. Keogh (Radiology)
- C. Marlowe, K. Dahle, C. Mengerink (Radiation
Therapy) - V. Morovan (Statistics)
Imaging Matters
25Questions?
26Supplementary Slides
27ResultsCT with Bowel Contrast
CT with Contrast
MRI
28ResultsCT with IV Contrast
CT with Contrast
MRI
29ResultsImaging and Registration
Registration Error 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
30ResultsContoured Tumour Volumes
CT
Fuse
31ResultsContoured Tumour Volumes PTVs
CT
Fuse
32Results Underestimate Tumour Extent
33ResultsContoured Tumour Volumes
34ResultsGross Tumour Volumes by Observer
35ResultsGross Tumour Volume By Patient
36ResultsMean Gross Tumour Volume By Patient
- CT volumes 1.2 times larger then fusion, p0.04
37ResultsMean PTV By Patient
38ResultsMeasuring Variation
39ResultsMEAN X,Y,Z Variation
Standard Deviation smaller for fusion all
directions All dimensions smaller for Fusion
(sup/inf most significant)
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
40ResultsVariation Superior to Inferior
41ResultsMedial 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
42ResultsCompletion Survey
- Survey completed for each image set at completion
of contouring (N88) - Linear Analog Rating Scale
- Rate the general quality of this CT (fusion)
image set? - (1 poor, 5-meets expectations, 10 exceeds
expectations) - CT score 4.9, Fusion 6.7
- 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 volume
- CT 4.0, Fusion 7.8
- b. Critical Structures
- CT 4.2, Fusion 7.4
Indicates Subjectively Better" Delineation of
Tumour and Critical Structures with Fusion
43ResultsRadiation 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
- CT 4.0, Fusion 7.8
- Normal Tissues
- CT 4.2, Fusion 7.4
Fuse
Fuse
CT
CT
poor meets expectations
exceeds
poor meets expectations
exceeds
Improved Delineation of Tumour and Normal
Structures with Fusion
44ResultsRadiation Therapists Opinions
- 8 question survey for Radiation therapists (n4)
involved in sarcoma fusions - Average time for fusion
- 35.5 minutes
- Usefulness of Fusion for delineating normal
structures - Extremely useful
- Difficulty of Performing Fusions compared to
other sites - Slightly more difficult, (extremities the most
difficult) - Important factors in image fusion
- Tumour location, MRI quality, time available
- IMMOBILIZATION and Position
-
45ConclusionsA Role for Fusion in Sarcoma Planning?
- CT/MRI fusion is valuable to the planning process
for sarcoma - Contoured Tumour Volumes
- More normal tissue included in the target volumes
with CT - Disease excluded on CT
- Volume Variation
- More consistency in contours with Fusion
- Completion Survey
- Radiation Oncologists and Therapists felt fusion
was valuable