Importance of 4D CT in stereotactic lung radiotherapy...
Transcript of Importance of 4D CT in stereotactic lung radiotherapy...
Importance of 4D CT For Target
Volume Definition in Stereotactic Lung
Radiotherapy
Derya Çöne, RTT
Acıbadem Kozyatağı Hospital
Istanbul, Turkey
Introduction
SBRT
• High local control rates for early
stage NSCLC
• High doses in1-5 fractions
• Limited margins
Introduction
Target delineation accuracy is very
important for success of the treatment
Intrafractional tumor movement
caused by breathing must be taken
into account when treating lung
tumors.
Introduction
Various techniques are being used for lung tumor target delineation including
4DCT, 3D MIP, 3D insp-exp or 3D free+margin.
However, the accuracy of some of these techniques to delineate the target is
controversial.
Introduction
Recommendations about delineation lung tumor for SBRT treatment
intend.
Introduction Another recommendation is coming from AAPM TG 101.
And it is directing us to the TG 76
Considerations of Breathing
Motion in CT Sim
Breath Hold CT Scan
• Voluntery breath hold
• Active breathing control
• Combine inhale and exhale GTVs to get ITV
Considerations of Breathing
Motion in CT Sim
Breath Hold CT Scan
• Voluntery breath hold
• Active breathing control
• Combine inhale and exhale GTVs to get ITV
Slow CT scan
• 4 seconds per slice for axial scan
Considerations of Breathing
Motion in CT Sim
Breath Hold CT Scan
• Voluntery breath hold
• Active breathing control
• Combine inhale and exhale GTVs to get ITV
Slow CT scan
• 4 seconds per slice for axial scan
Gated CT scan
• Images at only one phase, 4-5 times longer acquisition time
Considerations of Breathing
Motion in CT Sim
Breath Hold CT Scan
• Voluntery breath hold
• Active breathing control
• Combine inhale and exhale GTVs to get ITV
Slow CT scan
• 4 seconds per slice for axial scan
Gated CT scan
• Images at only one phase, 4-5 times longer acquisition time
4D CT scan
• 3D CT scans at multiple breating phases
Considerations of Breathing
Motion in CT Sim
Breath Hold CT Scan
• Voluntery breath hold
• Active breathing control
• Combine inhale and exhale GTVs to get ITV
Slow CT scan
• 4 seconds per slice for axial scan
Gated CT scan
• Images at only one phase, 4-5 times longer acquisition time
4D CT scan
• 3D CT scans at multiple breating phases
Processed image data sets
• Maximum intensity projections
• Avarage intensity projections
• Minimum intensity projections
Aim
In this study, we investigated if the ITV volume defined on 4D CT
images, received the prescription dose, when the target volume was
determined on Free Breath CT and MIP images for SBRT for lung
tumors.
Patients and Setup
Twelve patients treated with fractionated stereotactic body
radiotherapy for early-stage lung cancer or lung metastasis in our
clinic between June 2013 and December 2014 were included in this
study
Median age 69.5 (range 42-86y)
6 primary lung cancer, 6 metastases
Patients were immobilized with a vacuum bag in supine position,
arms extended above the head.
Methods CT scans were performed with 3mm slice thickness for 4D and free
breathing CT using Varian RPM system (Siemens Somatom
Sensetion 64).
Free Breathing CT GTV-FB contoured on Free Breathing CT
4D CT ITV was created by merging GTV contours defined on each phase of
the respiratory cycle (8 phases on 4D CT)
MIP 4D CT images were digitally processed to obtain maximum intensity
projection (MIP). GTV-MIP contoured on MIP images.
Methods: Contouring
PTV-FB and PTV-MIP volumes were created on free breathing (FB)
and MIP planning CT scans respectively (GTV+5mm).
CTV contour was not defined.
PTV-4D was generated by adding 5 mm margin to ITV
FB, MIP and 4D CT data sets were automatically matched
according to DICOM coordinates.
Methods
PTV-MIP and PTV-4D contours were transferred on the free breathing
CT scan
Plans were constructed on FB datasets for PTV4D (95% of PTV-4D
volume to receive 100% of the prescription dose).
This plan was defined as a reference plan.
Two treatment plans were generated for PTV-FB and PTV-MIP
volumes (95 % of PTV–FB and PTV-FB volumes to receive
100% the prescribed dose) on free breathing CT dataset.
Methods
Red GTV-FB
Magenta: GTV-MIP
Cyan: ITV
Methods: Planning
Prescription dose defined as 7x850 cGy=6000 cGy.
For treatment plans, 'RapidArc' technique was performed using 2
noncoplanar partial arcs (Eclipse Version 11).
AAA algorithm was used for dose calculation.
Grid size: 0.125 cm
Heterogeneity correction: ON
The ITV volume that received the prescription dose and dose received
by 95% of ITV volume (D95) were recorded for each plan.
Methods
Dose distribution for PTV-FB plan
Methods
Dose distribution for PTV-MIP plan
Results
Mean PTV-4D, PTV-MIP and PTV-FB volumes were 23.2 cc, 15.4cc
and 11cc, respectively
Plans for PTV-MIP volume: P PTV-MIP,
Plans for PTV-FB volume : P PTV FB
Conclusion
We found the ITV volume was not covered by the prescription dose if
the target volume was not defined on each phase of 4D CT .
Even, the MIP datasets constructed via 4DCT images were not
sufficient to reflect the respiratory effect.
4D CT scans should be considered as standard imaging modality for
stereotactic lung radiotherapy.
Thank you...