Technical Advances in radiotherapy for Lung (and liver) Cancer
Transcript of Technical Advances in radiotherapy for Lung (and liver) Cancer
Technical Advances in Radiotherapy for Lung (and Liver) Cancer
Peter Balter, Ph.D.
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)
Technologies for improvement in XRT of the thorax in the last 10 years
• 4DCT/Respiratory correlated imaging
• Motion management during treatment
• Intensity ModulatedRadiation Therapy
• Image Guided Radiation Therapy (IGRT)
• Protons
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
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.
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
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
4DCT of moving SBRT target
Same patient residual motion during breath-hold
Example: Lung SBRT case that required respiratory motion management
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
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.
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
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
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
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
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.
• The physics of protons may enable better sparing of normal tissues than the best IMRT/VMAT.
Protons: Better treatment through physics
Gillin
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Protons: Better treatment through physics
Protons(120 MeV4cm SOBP)
Electrons (20 MeV)
Photons(6 MV)
Rel
ativ
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ose
Depth in Water (cm)
In contrast to Electrons and Photons there is nearly perfect fall off at the end of the proton range Gillin
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 fractionationGillin
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
Thank you for your attentionAcknowledgments
• 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.