IGRT in Lung Cancer Dr Santam Chakraborty Assistant Professor Radiation Oncology
IGRT in Lung
CancerDr Santam Chakraborty
Assistant Professor
Radiation Oncology
IGRT
Image Guided Radiotherapy
Describes a chain rather than a single process
“Exclusive” of the delivery process
Typically “onboard” guidance utilized
Leads to action that improves / verifies accuracy
T. Gupta, C. A. Narayan, Image-guided radiation therapy: Physician’s perspectives. J. Med. Phys. 37, 174–
182 (2012).
Why IGRT
S. S. Korreman, Image-guided radiotherapy and motion management in lung cancer. Br. J. Radiol. 88,
20150100 (2015).
Why IGRT ...
J.-J. Sonke, J. Lebesque, M. van Herk, Variability of four-dimensional computed tomography patient models. Int. J. Radiat. Oncol.
Biol. Phys. 70, 590–598 (2008).
Target Volume Changes due to Imaging
S. S. Korreman, Image-guided radiotherapy and motion management in lung cancer. Br. J. Radiol. 88,
20150100 (2015).
FDG PET CT in Target Volume Delineation
Y. Zheng et al., FDG-PET/CT imaging for tumor staging
and definition of tumor volumes in radiation treatment
planning in non-small cell lung cancer. Oncol. Lett. 7,
1015–1020 (2014).
● 35% have change in stage
assignment
● Fused CT / PET result in target
volume changes in 60%
● Reduced variability seen in
GTV delineation between
observers.
IGRT Technology & Imaging
Image Guided RT
Ionizing Radiation Based Other Technologies
Planar Imaging Volumetric Imaging
KV Fluoro / X ray
MV Fluoro / X ray
KV CT
MV CT
Electromagnetic Tracking
Optical Surface Tracking
Ultrasound Tracking
MRI based Tracking
IGRT Image Technologies
Technology Energy Type Accuracy Comments
EPID MV 2D 1-2 mm Surrogate imaging of soft tissue
KV Xray KV 2D 1-2 mm Better resolution w.r.t. EPID
CBCT KV 3D < 1mm Volumetric “slow” scan.
MVCT MV 3D < 1mm Can be useful for adaptive radiotherapy
Stereoscopic Xray KV 2D < 1mm Useful in tumor tracking. Oblique angles.
USG - 3D 3 mm Main utility in prostate cancers
Surface - 2D 1 mm Surface based optical tracking and localization
Transponders - 2D - Independent system for tumor tracking
IGRT Issues in Lung Cancer
1. Lung tumors are difficult to see with megavoltage imaging.
1. Significant movement of the tumor in all 3 directions in addition to “hysteresis”
1. Significant changes in the course of treatment
1. Lung motion is independent of bony motion
Difficulty in
Visualization
EPID based matching
Difficulty in
Visualization
Changes in
Volume
K. R. Britton et al., Assessment of Gross Tumor Volume Regression and Motion Changes
During Radiotherapy for Non–Small-Cell Lung Cancer as Measured by Four-
Dimensional Computed Tomography. International Journal of Radiation
Oncology*Biology*Physics. 68, 1036–1046 (2007).
Changes in
Volume
L. A. Dawson, M. B. Sharpe, Image-guided radiotherapy: rationale, benefits, and limitations.
Lancet Oncol. 7, 848–858 (2006).
Changes in
Volume
Ways to implement IGRT
IGRT Protocols
Offline Online
Q : Which one can correct for random errors?
➢ Large step
reduction
➢ Limited workload
➢ Mean error
correction
➢ Allows larger dose
through smaller
margins
➢ Daily error
correction
Basic points prior to Imaging
1. Reproducible comfortable positioning with immobilization
2. Tattoos help but skin marks mobile over bone (~ 5 mm)
3. Laser alignment is must
4. Rigid couchtop with indexed immobilization
5. Assume setup is incorrect unless proven otherwise
Bone Matching vs Soft Tissue Matching
M. Guckenberger, Image-guided Radiotherapy Based on Kilovoltage Cone-beam Computed Tomography — A Review of Technology and
Clinical Outcome. European Oncology & Haematology. 07, 121 (2011).
Good CBCT Match
Slide Image
courtesy Dr J P
Aggarwal
(TMH)
What to match on CBCT
4D-CBCT
https://www.aapm.org/meetings
/06ss/documents/SonkeConeBe
am.pdf
Systematic vs Random Error
Systematic error : Reproducible, consistent errors, occurring in the same
direction and of similar magnitude.
It affects the dose distribution by producing a “miss”
Defined as the AVERAGE of a set of displacement.
Random error: Varies in direction and magnitude in each fraction.
It affects the dose distribution by producing a “blur”
Defined as the STANDARD DEVIATION of a set of displacements
Example Systematic & Random Error
https://docs.google.com/spreadsheets/d/1_w1dJzakVPJeMqFFRr5PZs4MVmKrN4lFPIMr0tRHZWA/edit?usp=sharing
NAL correction
workflow
Example of a NAL protocol
Levels of IGRT implementation
0 1 2
RT Planning
Done more
accurately
(e.g. contrast /
PET CT /
4DCT)
3 4
Surrogate
based
matching
using bony
anatomy
Matching
based on
target
anatomy
(implanted
markers /
volumetric)
Adjustment /
correction for
intrafraction
motion
Adaptive
Radiotherapy
National Cancer Action Team, “National Radiotherapy Implementation Group Report IGRT Final Guidance for Implementation and Use”
(NHS, 2012), (available at link).
IGRT Lung Recommendation
Level 0 CT with contrast
PET CT for accurate target delineation
4DCT for accurate capture of motion
For all patients
Level 1 Planar imaging with matching to reliable bony surrogate
± volumetric imaging weekly (tumor morphology / volume changes)*
Pancoast tumors
3DCRT
Level 2 Imaging with offline matching and NAL pathway with target volume
matching (volumetric / fiducial)
± volumetric imaging weekly (tumor morphology / volume changes)*
All other lung tumors
3DCRT
Level 2 Imaging with daily online correction with target volume matching
(volumetric / fiducial)
Complex IMRT /
Boost or reduced
margins
Level 3 Intrafraction motion monitoring SABR
National Cancer Action Team, “National Radiotherapy Implementation Group Report IGRT Final Guidance for Implementation and Use”
(NHS, 2012), (available at link).
Imaging Dose & consequences
Modality Effective Dose (mSv) Daily IGRT (30#)
Diagnostic Chest CT 6.4 -
EPID AP 3.6 246
EPID Lat 4.6
KV CBCT 24.6 738
KV XVI (Elekta) 8.1 243
Estimated life-time probability of 2nd malignancy : 1.2% - 3.7%
M. J. Murphy et al., The management of imaging dose during image-guided radiotherapy: Report of the AAPM Task
Group 75. Med. Phys. 34, 4041–4063 (2007).
Conclusions
● Image guided radiotherapy is an integral part of any conformal radiotherapy
program for lung cancer
● IGRT allows safer radiotherapy in terms of OAR dose reduction.
● IGRT however needs specialized equipment and expertise
● A team effort is needed for commissioning and implementation
● Physics and Technologists need to be a part of the team !!