Radiation Protection in Radiotherapy

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Radiation Protection in
Radiotherapy
Albert Lisbona
Medical Physics Department
CLCC Nantes Atlantique
44805 – Saint-Herblain
France
[email protected]
Centre de Lutte Contre le Cancer
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Radiation therapy
• The lecture is oriented to the patient
optimisation radiation therapy treatment :
– Intensity Modulated Radiation Therapy (IMRT)
• Head and Neck, prostate,
– Respiratory gated radiotherapy
– Image Guided Radiation Therapy (IGRT)
which is not a treatment technique but an
imaging technique used for patient setup
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External Radiotherapy
Dose variations between 5
to 10% to the target
volume can lead to a
significant change in the
local tumor control and/or
in the toxicity
• Random errors
– Human factor
• Systematic errors
– Network, TPS, beam
calibration,...
IMRT medical Justification
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• Medical justification :
– IMRT two objectives :
• Dose limitation to OAR to decrease toxicity,
• Dose escalation to target to increase local control
– Dose limitation to :
• Spinal cord,
• Parotids (to preserve salivary function)
• Rectal wall and bladder wall
IMRT
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• IMRT : to modulate static or rotational xray
beams in order to get a better target
coverage AND a good healthy tissue
sparing
– Prostate cancer
• rectum, bladder,
– H&N cancer
• parotids, cord, oral cavity.
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Qualitative and quantitative
3D CRT
IMRT
evaluation
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3D CRT
Qualitative and quantitative
evaluation
IMRT
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Qualitative evaluation
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3D CRT
IMRT
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Quantitative evaluation
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3D CRT
IMRT
3DCRT 4 beams 90°
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3DCRT 5 beams 72°
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5 beams 72° + IMRT
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Respiratory gated radiotherapy
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Respiratory gated radiotherapy
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Justification
¾ Problems with 3D CRT or IMRT
• How to reduce radiation field size to protect closed healthy
tissue ?
• Limitation : lack of precise data on organs movements =>
empirical margins from 1.5 cm à 2 cm
¾ Main organs concerned by respiration
• Chest : lungs, heart, esophagus, diaphragm, mediastinum,
breasts
• Abdomen : liver, kidneys, pancreas, spleen
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Tumor position variation during respiratory cycle
Right lung dilatation variation
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M. Ayadi CLCC Lyon
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M. Ayadi CLCC Lyon
Dose distribution calculated from Internal Target
Volume defined on CT
ITV superposition obtained from a 4D CT showing
=> Under coverage of 4DITV
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M. Ayadi CLCC Lyon
"Respiratory" lung showing the superposition of calculated
isodoses lines from a 3DCRT on an "averaged" 4DCT
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M. Ayadi CLCC Lyon
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IGRT
• IGRT is an advanced technique (using
imaging devices) that allows radiation to be
delivered to tumors with more precision
than is traditionally possible.
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IGRT
• If we can :
– Improve, patient setup (reproducibility),
– Reduce uncertainties on patient movements (intra,
interfractions),
– Reduce uncertainties on target movements (intra,
interfractions).
• So we could :
– Reduce margins around targets used to take into account
movement,
– Obtain a possible strategy to adapt to target modifications,
or to the patient,
– Obtain the opportunity to increase dose.
Imaging techniques for IGRT
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• Electronic Portal Imaging Device :
– Portal images of radiation patient fields
– Implanted fiducials (gold seeds)
• Stereoscopic kV imaging
• Cone Beam Computed Tomography (CBCT)
– kV
– MV
• Echography
• CT Scanner in linac vault
• MVCT Tomotherapy
Cone Beam Computed Tomography
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Setup
Adjustment
Patient alig
Reconstruction
Acquisition
CBCT
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Example : prostate
CT slices
CBCT slices
CBCT Reconstruction
Skull
H&N
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Lung
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Bladder
Spine
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Conclusion
• Optimisation in radiotherapy for patient can be apply :
– To reduce target margins,
– To increase (or at least to keep) dose to the targets,
– To reduce dose to healthy tissues (organs).
• From medical community we need more evaluation
studies :
– tumor control, treatment complication rates, and patient
survival.
• Adequate staff, and sufficient training for all the members of
the team involved.
• Guidance, recommendation on quality assurance for new
techniques.
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GRACIAS
THANK YOU