Dose Accumulation

Deformable Registration
and Dose Accumulation
for Liver StereotacticBody Radiotherapy
Michael Velec
Liver SBRT
• Planning:
– Individualized, highly conformal
– Rx based on liver NTCP
– Goal: ↑tumor dose, ↓normal tissue
dose
• Image-guided RT (IGRT):
–
–
–
–
Planning CT
3D soft-tissue targeting
3D motion quantification
Rigid liver registration
Goal: Planned = Delivered dose
Treatment CBCT
9/21/2011
Rationale
• Deformable image registration
(DIR)
– Morfeus: biomechanical DIR
– Accuracy < 2 mm in the liver
– Allows tissue tracking
• 4D CT Dose accumulation
– ∆ in min tumor up to 15%
– ∆ in max normal tissue up to 25%
– Planned Dose ≠ Predicted Dose
How well do the Planned and
Predicted doses compare to
what is actually delivered?
9/21/2011
17 mm
12 mm
8 mm
4D CT Breathing Map
Rationale
• Deformable image registration
(DIR)
– Morfeus: biomechanical DIR
– Accuracy < 2 mm in the liver
– Allows tissue tracking
• 4D CT Dose accumulation
– ∆ in min tumor up to 15%
– ∆ in max normal tissue up to 25%
– Planned Dose ≠ Predicted Dose
How well do the Planned and
Predicted doses compare to
what is actually delivered?
9/21/2011
Predicted – Planned Dose
Methods I – Clinical Data
• N=30 previous SBRT patients
– Primary 50%, Mets 50%, # GTVs 1 – 5
– Free-breathing 36%, Compression plate 64%
• Rx: 27 – 60 Gy in 6 fractions over 2 weeks
– Planned on Exhale 4D CT
– Clinical-IGRT: 2D Fluoroscopy + 3D CBCT
– IGRT tolerance: 3 mm
• Full dose accumulation with MORFEUS
– Daily 4D CBCT in the treatment position
– External, Liver and Spleen contoured on 4D CBCT
9/21/2011
Methods I – Dose Accumulation
Part A
Predicted Accumulated
Dose, Dacc
Dose, Dpred
Planned, Dplan
╳ 6 fractions
Exhale 4D CT
Exhale 4D CBCT
Inhale 4D CT
Inhale 4D CBCT
9/21/2011
Methods I – Dose Accumulation
Part A
Predicted Accumulated
Dose, Dacc
Dose, Dpred
Planned, Dplan
Exhale 4D CT
╳ 6 fractions
Exhale 4D CBCT
Part B
• Extract impact of interfraction geometric
uncertainties on dose:
– Residual Setup Errors
• Rigid liver-liver error
• Exh CT vs Exh CBCT
– Abdominal Deformation
Inhale 4D CT
Inhale 4D CBCT
• Rigid registration vs.
DIR
• Exh CT vs Exh CBCT
– Breathing Variations
• DIR of 4D CT vs 4D
CBCT
9/21/2011
Results I – Geometric Uncertainties
DIR of 4D CBCT revealed geometric uncertainties
for the tumor that exceeded the clinical IGRT
tolerance (3 mm):
• Exhale CT to Exhale CBCT
– 30% of patients (n=9) had residual systematic errors >3
mm (maximum systematic error: 11 mm)
• Exhale CBCT to Inhale CBCT (vs. 4D CT)
– 53% of patients (n=16) had mean ∆ in breathing motion
>3 mm (∆ amplitude motion of -11 to 8 mm)
9/21/2011
Results I – Dose Accumulation
∆ Dose (% of Rx)
*p < 0.05
Dacc - Dplan
Mean (SD)
Dacc - Dpred
Range
Mean (SD)
Range
Tumor min
-0.8 (3.3)
-14.6
4.5
0.2 (4.0) -14.2 13.4
Liver mean
-0.6 (1.6)
-5.8
2.5
-0.1 (1.6)
-5.1
2.6
Bowel max
-3.2 (4.0)
-15.0
2.7
-0.8 (3.8)
-6.6
9.9
*
Duodenum max
-4.6 (8.6)
-41.9
2.6
-0.9 (7.6) -38.4
9.1
*
• Proportion of patients with Dacc |∆| > 5% to any tissue:
– 70% (n=21) relative to the Planned Dose (Dplan)
– 53% (n=16) relative to the Predicted Dose (Dpred)
9/21/2011
Results I – Dose Accumulation
∆ Dose (% of Rx)
*p < 0.05
Dacc - Dplan
Mean (SD)
Dacc - Dpred
Range
Mean (SD)
Range
Tumor min
-0.8 (3.3)
-14.6
4.5
0.2 (4.0) -14.2 13.4
Liver mean
-0.6 (1.6)
-5.8
2.5
-0.1 (1.6)
-5.1
2.6
Bowel max
-3.2 (4.0)
-15.0
2.7
-0.8 (3.8)
-6.6
9.9
*
Duodenum max
-4.6 (8.6)
-41.9
2.6
-0.9 (7.6) -38.4
9.1
*
• Proportion of patients with Dacc |∆| > 5% to any tissue:
– 70% (n=21) relative to the Planned Dose (Dplan)
– 53% (n=16) relative to the Predicted Dose (Dpred)
9/21/2011
Results I – Dose Accumulation
% Δ Max Bowel (0.5 cc)
15
10
5
0
-5
-10
-15
9/21/2011
Accumulated – Predicted
Results I – Dose Accumulation
% Δ Max Bowel (0.5 cc)
15
Accumulated – Predicted
10
5
0
-5
-10
-15
9/21/2011
Residual Setup Errors
Deformation
Breathing Variations
Methods II – DIR-IGRT
1. DIR between exhale CT
and exhale CBCT
•
GTVs
Liver
2. Translate patient model
to correct tumor (‘DIRIGRT’)
•
Tumor
displacement
on
exhale CBCT, modeled with
biomechanical DIR
9/21/2011
Calculate centre-of-mass
(COM) tumor motion
AVG COM ∆ for multiple
tumors
3. Compare Dacc with DIRIGRT to Clinical-IGRT,
relative to Dpred
Results II – Dose Accumulation
Clinical-IGRT Dacc
Vs.
Predicted Dose
DIR-IGRT Dacc
Vs.
Predicted Dose
Pts with
Max Min
Pts with
Max Min
|∆| ≥ 5%
%∆of Rx
|∆| ≥ 5%
%∆of Rx
Min Tumor
10 %
-14
13
7%
-6
4
Mean Liver
3%
-5
3
0%
-4
3
Max Bowel
20 %
-7
10
17 %
-6
8
7%
-38
9
17 %
-21
7
Max Duodenum
DIR-IGRT Dacc Vs. Predicted dose:
50% overall of patients overall have still |∆| > 5%
9/21/2011
Conclusions
• Direct tumor targeting (e.g. DIR-IGRT) for IGRT,
reduces dose deviations relative to the
Predicted Dose
• Deformable dose accumulation over the course
of SBRT is warranted to reduce the
uncertainties in the dose record
9/21/2011
Future Directions
• Optimize the Predicted 4D dose distributions’
treatment margins and dose gradients
• Investigate the potential for margin reduction and
dose escalation with DIR-IGRT
• Adaptive re-planning may be warranted to correct
for deformation and breathing changes
• Correlate accumulated doses with clinical
outcomes
9/21/2011
9/21/2011