Improving precision in imaging and treatment for radiotherapy - - PowerPoint PPT Presentation

Improving precision in imaging and treatment for radiotherapy

Marcel van Herk E-mail: portal@nki.nl On behalf of the image-guidance team Netherlands Cancer Institute Amsterdam, the Netherlands

Classic radiotherapy procedure

Tattoo, align and scan patient Draw target and plan treatment on RTP Align patient on machine on tattoos and treat (many days)

In principle this procedure should be accurate but …

Things are uncertain!

Imaging and delineation Treatment

Improving precision in imaging

• Improve image acquisition to collect representative data
• MRI: DTI, CE
• 4D CT, 4D PET
• Image post-processing
• Training and consensus
• Gather clinical knowledge
• Can we close the diagnostic gap ?

Advanced imaging under treatment conditions: 4D PET/CT

Free-breathing treatment requires free-breathing imaging

• Shows correct tumor shape

and its components

• Shows range of respiratory

motion

• Allows optimal tumor

targeting taking motion into account

Post-processing to Mid-position CT: clinical at NKI since 6 months

4DCT 4D DVF Deform 4DCT to local mean pos. Mid-position CT

Average frames Deformable registration Wolthaus et al, Med Phys 2008

7

Mid-ventilation versus mid-position reconstruction (deformable registration) for free-breathing CT

Mid-ventilation (one bin) Median of all bins deformed pixel by pixel to mid-position

CT (T2N2) SD 7.5 mm CT + PET (T2N1) SD 3.5 mm

Delineation variation: CT versus CT + PET

Steenbakkers et al, IJROBP 2005

Effect of training and peer collaboration on target volume definition

teacher students groups

Material collected during ESTRO teaching course on target volume delineation

But what about the CTV ?

• By definition disease between the GTV and

the CTV cannot be detected

• Instead, the CTV is defined by means of

margin expansion of the GTV and/or anatomical boundaries

• Very little is known of margins in relation to

the CTV

• Very little clinical / pathology data
• Models to be developed

Hard data: microscopic extensions in lung cancer

30% patients with low grade tumors (now treated with SBRT with few mm margins), have spread at 15 mm distance

Having dose there may be essential!

100% 50% 25%

The impact of microscopic disease on the tumor control probability in non-small-cell lung cancer. Christian Siedschlag et al, R&O 2011

N=32

10 20 30 40 50 60 70 80 90 100 5 10 15 20 25 30 35 40 45

distance from GTV [mm] % cases with extensions

Deformation corrected

Estimate pattern of spread from response to incidental dose in clinical trial data (high risk prostate patients)

Average dose no failures – average dose failures ≈ 7 Gy p = 0.02

72 60 48 36 24 12 1.0 0.8 0.6 0.4 0.2 0.0

< median (53.1 Gy)

Treatment group IV, Hospital A (n=67)

≥ median

p = 0.000 100%

0%

3 6 Y 80% 60% 40% 20%

• =

PSA controls PSA failures

Witte et al, IJROBP2009; Chen et al, ICCR2010

How to detect microscopic disease ?

• Closing the diagnostic gap: the cancer spread

too big to respond to drugs but too small to be visible on diagnostic images

• Optical techniques such as optical coherence

tomography may be the future

In vivo esophagus; 10 µm voxel size

Image guidance thoughts

• There is currently a trade-off between IGRT

imaging speed and quality of information Fast: 2D for bone / markers Slower: 3D for soft tissue guidance Still slower: 4D for moving structures Slowest: ART: use many days scans to adapt to deformations

Optimal choice depends on frequency distribution of organ motion

Are markers perfect ?

Apex Base

• Sem. Vesicles

à +/-1 cm margin required van der Wielen, IJROBP 2008 Smitsmans, IJROBP 2010

Best: combine markers with low dose CBCT

Seeds allow low dose imaging

0.35 mm Visicoils Seeds and soft tissue (seminal vesicles) visualized in low dose 1 minute scan Daily image guidance using markers for prostate body ART after one week based on position of the seminal vesicles

0.4 cGy 3 cGy

3D imaging is problematic when motion occurs during scanning

Alternative: 4D IGRT imaging, but scan time is quite long

Reconstructed 3D CT image One backprojection

Challenge: 3D acquisition blurred and 4D acquisition slow

Reconstructed CT image One backprojection

Solution: in-line motion compensated reconstruction (motion estimated prior in 4D planning CT)

Long scan (4 min) Short scan (1 min)

Non-corrected (3D) CBCT

Long scan (4 min) Short scan (1 min)

Motion-compensated CBCT

In clinical use at AVL since January, 2012

Differential motion

No couch correction can solve this problem

Planning CT 4D-CBCT CTV

Adaptive RT using an average patient model

<DVF> DVF

Open issue: efficient implementation for those patients that need it

Conclusions

• Target volume definition is by far the weakest link in

radiotherapy

• New imaging tools, but in particular consensus and

consultation are important ways to improve this situation

• To improve CTV definition, analysis of large outcome

databases is necessary

• Improvements in image guidance are still being

made: but the most difficult step - adaptation to complex deformations - remains to be made in clinical practice

Thank you for your attention