IMRT For Prostate Cancer

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IMRT For Prostate Cancer
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Prostate CancerSeveral Basic Postulates

• Dose escalation is important
• Prostate is a moving target
• It needs to be hit with high precision every day
• DVH assessment
• Seminal vesicles to treat or not to treat

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Dose Escalation Is Important
M.D.Anderson figures 78 vs. 70Gy
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Some Images from Internet Sites
University of Nebraska internet site
Variantm Website
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The Prostate Is a Moving Target
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Margins
Margins 0.7cm LR 0.7cm SI 1.1cm AP
Antolac at al, IJROBP,42661, 1998
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What Could the IMRT Offer?

• Wraps the isodoses around critical structures

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Rectal Sparing
95
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What Is Rectum and How The Definition Is
Related to the DVH
Solid organ Hollow
organ
IMRT
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95
95
3D
95
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DVH Is a Form of Statistics
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The Way Ahead

• More sophisticated planning
• 3D (4 field brick is not good enough)
• IMRT
• when seminal vesicles to be treated
• Daily verification is more important

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Daily Verification Cone Beam Reconstruction

• Megavoltage CBR - Siemens
• MVision Megavoltage Cone Beam Imaging
• No extra attachments
• Dose per image 8MU
• Flat panel dependent

Orthovoltage CBR - Siemens Varian Additional
low energy system Better soft tissue
definition Lower dose per image Higher BED
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Fan vs. Cone Beam Reconstruction
detectors
detectors
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Cone Beam Uses Cone Beam of X-rays
This is volume acquisition All slices are
obtained in one go Actually slices do not
exist Single gentry rotation 210 degrees
(270-110)
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45 Seconds

• Uses the standard imaging plate
• Higher dose - better image
• Beautiful images - 15MU
• Useful images - 8MU
• With experience - 4MU

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Cone Beam Images are Good Enough for RT Planning

• Good CT density representation
• Metal hips are not a problem (pair production)
• Only problem - no patients contour (small field
  of view)

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Megavoltage Cone Beam ImagesMVision
Megavoltage Cone Beam Imaging
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Megavoltage Cone Beam ImagesMVision
Megavoltage Cone Beam Imaging
Seeds Insertion
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Cone Beam Image Dose Distribution

cone beam
original plan
no optimization
simple optimization
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Dose Escalation by Being More Accurate

• Prostate tumors stay posteriorly
• We are missing the tumor in at least 10 of the
  cases even with 1cm post margin
• Assuming daily verification eliminates the
  geographical miss
• By daily verification affectively we are
  increasing the tumor dose with 10
• Rectal dose would be the same or lower

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Summary

• The jury is still out on the role of IMRT in
  prostate cancer
• IMRT plans should be compared with good 3D plans
• Protons treatment becomes strongly promoted
  alternative
• IMRT certainly is very helpful for RT to the
• Seminal vesicles
• Pelvic nodes
• Pelvic nodal treatment is used less and less
• There is huge monetary drive behind IMRT in
  prostate cancer
• Daily verification is the next big thing in
  prostate radiotherapy

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• This presentation is done with close co-operation
  with