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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0.0

20.0

40.0

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80.0

100.0

120.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0

120 Mev 4 cm SOBP20 MeV

Protons: Better treatment through physics

Protons(120 MeV4cm SOBP)

Electrons (20 MeV)

Photons(6 MV)

Rel

ativ

e D

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.