This document summarizes recent technical advances in radiotherapy for lung and liver cancer, including: 4DCT imaging to account for tumor motion; motion management techniques like gating and breath-holding; intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) to improve dose conformity; image-guided radiation therapy (IGRT) to reduce margins and enable adaptations; and proton therapy which may further reduce normal tissue dose due to its physical properties, though proton techniques are still evolving to address motion and anatomical changes. The document outlines the benefits and challenges of each technique through examples and studies.
2. Disclosure
• Dr. Balter is PI on a sponsored research
agreement with Philips Medical Systems.
• Dr. Balter is co-PI on a sponsored
research agreement with Varian Medical
Systems (who is sponsoring my presence
in Thailand for the SBRT conference)
3. Technologies for improvement in XRT of
the thorax in the last 10 years
• 4DCT/Respiratory
correlated imaging
• Motion management
during treatment
• Intensity Modulated
Radiation Therapy
• Image Guided
Radiation Therapy (IGRT)
• Protons
4. 4DCT/Respiratory correlated imaging
• Allows determination of the position of tumor
over the entire respiratory cycle with respect to
– Critical structures
– Boney Anatomy
• Allows the design of a treatment plan
– Resilient to respiratory motion
– Timed with respiratory motion (gating)
• Demonstrates the need to mitigate motion
– Breath-hold
– Abdominal compression
5. General approach to 4-D image acquisition
• Acquire image data continuously during respiration
• Reconstruct the image data at specific phases in the
respiratory cycle for each patient location.
• Combine image data at same phase from several
respiratory cycles.
• Result: A series of 3-D CT scans each representing a
different phase in the respiratory cycle.
6. Standard Treatment
Internal Target Volume (ITV) approach:
• Treat track of tumor motion
• Based on a 4-D dataset
• Custom margins for each tumor
ITV
Motion management during treatment
7. Gating
• Dynamic: Deliver dose when tumor is within the beam
portal
• Breath-hold: Ask or force the patient to hold their breath
at a given level then deliver the beam
Generally done with visual feedback
Motion management during treatment
8. 4DCT of moving
SBRT target
Same patient
residual motion
during breath-hold
Example: Lung SBRT case that required
respiratory motion management
9. Intensity Modulated Radiation Therapy (IMRT)/
Volumetric Modulated Arc Therapy (VMAT)
• A computer optimizer with a skilled operator
designs a plan based on clinical requirements
(inverse planning)
– create highly conformal dose distributions
– simultaneously treat to several dose levels
– compensate for non-uniform
scatter at the lung tumor interfaces
– To quantify and control
normal tissue dose
10. IMRT/VMAT learning curve
• Observations and prospective :
– MDACC: IMRT plan quality in 10 years ago is
significantly different from the plan quality now with
the same planning and delivery systems.
– Publications:
• An external audit of IMRT plan showed that an
experienced center can yield superior IMRT plans
• Doismetrists with higher level of IMRT experience
produced a better quality head and Neck IMRT plan.
11. Automated IMRT Optimization Tools
• Auto-plan Systems (In-house and commercial)
– Improves consistency and overall quality of plans
• Multicriteria Optimization (commercial)
– Provides real-time feedback of plan objective
trade-offs
• These tools allow all centers to achieve high
quality IMRT
12. Image Guided Radiotherapy (IGRT)
• High quality/low dose imaging has become
a standard feature of our linear accelerators
• Enables:
– Reduced margins
– Gating with verification
– Hypo-fractionation (SBRT)
– Adaptive planning
• Adapt to changing anatomy
13. IGRT based targeting in the Thorax
• Projection Imaging
• Allows setup to boney
anatomy
• Allows setup to implanted
markers
• Has been show to greatly
reduce systematic setup
errors
• Volumetric Imaging
• Allows direct setup to soft
tissue lesions
• Allows evaluation of
anatomical changes
14. Adaptive Planning-Thorax
• Many tumors/patients change size and shape during
the course of radiotherapy
• Normal anatomy/breathing pattern can change more
• If we do not adapt to these changes
– We may miss tumor
– We may overdose normal anatomy
– We may miss an opportunity to dose escalate
• Thorax – big cavity where tumor, fluid and air
can all change places with no external
indication
– Often the goal of radiotherapy is to open airways
which then cause changes in internal anatomy
15. 10/11/2010 – 0 days treatment-4 days after sim
Simulation CT
Daily CBCT Daily CBCT
Daily CBCT
On-treatment soft tissue imaging demonstration of the need for
adaptive planning due to changes in breathing pattern.
16. • The physics of protons may enable better sparing
of normal tissues than the best IMRT/VMAT.
Protons: Better treatment through physics
Gillin
17. -20.0
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Protons: Better treatment through physics
Protons
(120 MeV
4cm SOBP)
Electrons
(20 MeV)
Photons(6 MV)
RelativeDose
Depth in Water (cm)
In contrast to Electrons and Photons there is nearly
perfect fall off at the end of the proton range Gillin
18. Example thorax case: Protons have a limited range,
which should limit toxicity (no low dose bath)
Patient with T2, N0, MX
COPD
87.5 CGE
Limited dose to the non-
involved lung
Note:
Penetration
through
lung
3 fields,
Lateral
and 2
Posterior
obliques
Standard fractionation
Gillin
19. Protons: Opportunities
• The same physics that helps protons better spare tissues makes them
much more sensitive to uncertainness
– Scattered protons have poor proximal coverage, sine the beam is
designed for distal edge
– Respiratory motion
– Anatomical changes
• Protons technologies are still evolving quickly to mitigate these issue
– Intensity modulated proton therapy
– Robust optimization
Dong
20. Thank you for your attention
Acknowledgments
• Zhongxing Liao, M.D.
• Joe Chang, M.D., Ph.D.
• James Cox, M.D.
• Ritsuko Komaki, M.D.
• many others
• Lei Dong, Ph.D.
• Radhe Mohan, Ph.D.
• Michael Gillin, Ph.D.
• George Starkschall, Ph.D.
