IMRT and Retreatment

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• IMRT and Re-treatment

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Retreatment

• One of the most challenging areas in radiotherapy
• Frequently needs to be done on semi-urgent basis
• The normally quoted organ tolerances still needs
  to be respected

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Organ Tolerances

• What is radiation tolerance
• Is 45Gy really the tolerance of the spinal cord
• How much repair occurred since the last treatment
• We do not have good answers to all these
  questions but as doctors we have to make a
  decision

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Organ tolerance vs. Physician ToleranceThe
Spinal Cord Example

• TD5/5 vs TD100/5
• 45Gy will never cause damage of spinal cord (50Gy
  is probably TD5/5)
• 70Gy will almost always cause damage of spinal
  cord
• Walking the thin line between 45 and 70Gy

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Things to consider

• The risks of retreatment need to justified on
  clinical basis
• Consequences if we dont treat
• The chance of response
• The tumor already had radiotherapy
• We may have selected resistant clones
• The patient view
• There is no substitute for good informed consent
• Technology available
• IMRT
• Daily verification

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Technology availableIMRT

• Sparing the organs at risk
• Sparing of the previously irradiated tissues
• Delivering of highly conformal treatment

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Previously irradiated tissues

• IMRT is able to consider previous isodose clouds
  as sensitive structures
• DICOM-RT problem two different entities
• The dose matrix
• The organ contours
• None of the current planning system can bridge
  the gap between isodose clouds and structure sets

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Lets do it by handExample

• 25y old man with rhabdomyosarcoma of the left
  ethmoid sinus
• Chemotherapy
• Radical course of radiotherapy 50.4Gy
• Now presents involvement of the CSF and symptoms
  of spinal cord compression
• MRI diffuse meningial involvement
• Deposit at T8 level
• No visceral disease
• For craniospinal radiotherapy

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The problem
The base of the brain has been already irradiated
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Dose tolerancesWalking the thin line

• The patient needs radiotherapy
• Without treatment the outcome is fatal
• Chemotherapy is unlikely to control the disease
• Beyond 66Gy brain necrosis is very likely
• 60-66Gy is the ceiling of the total dose
• The rest of the craniospinal axis needs at least
  36Gy

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The Prescription

• Craniospinal axis 36Gy
• Extra boost to 50.4Gy to the spinal deposit
• Area that previously was irradiated
• To 47Gy 20Gy
• To 35Gy 31Gy
• To 25Gy 36Gy
• To 12Gy 36Gy

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Manually draw the isodose lines as contours
Planning CT in the same position
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The final cranial plan
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Re-treatment of lesions close to spinal cord

• The problem with tolerances is still the same as
  with brain
• Usually larger fractions have already being used
• The accurate fixation is not really possible
• We need to hit with high precision a moving
  target
• IMRT
• IGRT

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Spinal column lesions re-treatmentExample

• 62 year old man
• Presented with symptoms of early spinal cord
  compression 1 year earlier
• CT
• lung lesion involving the vertebral body of T4
• several small lung lesions in keeping with
  metastatic disease
• Biopsy Squamous Cell Carcinoma
• Urgent course of radiotherapy 30Gy in 10
  fractions - POP

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Further History and Current Presentation

• Very good initial responce
• full power recovery
• pain resolution
• radiological improvement
• Resent presentation
• again symptoms of early spinal cord compression
• difficult to control pain
• CT scan
• progression of the disease at T4
• very minimal visceral disease

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The Dilemma

• The spinal cord already received 30Gy in 3Gy per
  fraction
• Equivalent ID2 dose 36Gy
• The useful palliation would need around 30-36Gy
  in view of previous treatment

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The Prescription

• Spinal Cord - to be avoided
• Area Around the actual cord - 20Gy
• The tumor - 36Gy in 20

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The plan
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The Positioning Part - Axial View
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Sagital and Coronal View
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Fusing CB with Planning CT
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• This presentation is done with close co-operation
  with