IMRT Protocol

Clinical implementation of
intensity-modulated
radiation therapy
Disclaimer
• This presentation is intended for internal
training.
• It is not intended for presentation to
customers.
IMRT solution
• Components
– CT simulator
– Eclipse treatment planning system for
3DCRT
– Helios inverse planning system for IMRT
– VARiS Vision information system
– Clinac linear accelerator
•
•
•
•
Millennium MLC (52, 80, or 120)
Dynamic MLC software
Exact Couch
PortalVision
Case presentation
• To illustrate the IMRT process, imagine
following a patient through this process:
• Patient selection
• Immobilization
• CT Simulation
• Treatment planning
• Plan review and approval
• Treatment delivery
• Portal imaging
Patient selection
•
•
Not all patients can nor should receive IMRT
Patients not suited for IMRT include:
– uncooperative patients
– patients in pain (unable to remain still throughout
treatment)
– obese patients
(entire external contour must be visualized on the CT
scan)
Patient selection
• Ideal patients for IMRT have these types of
tumors:
–
–
–
Irregularly-shaped tumors
Tumors that wrap around healthy organs
the body easy to setup
(Head and neck tumors are easy to setup. Tumors in the
abdomen are difficult to setup.)
– Tumors that are nearby critical normal structures
Immobilization
IMRT requires high-precision immobilization devices to ensure
patient setup reproducibility.
• All devices are fixed to the
treatment table and
indexed.
– Digital photographs are
used to communicate the
setup and immobilization.
– CT scanner, Acuity, Clinac
have matching Exact Couch
table tops.
• Time to construct: 30 min.
Varian’s patented Exact Couch table top
CT simulation
• A CT scan of the region of
interest is acquired.
– 3 mm slice thickness, or less,
for high-quality DRRs
– Intravenous contrast
• Improve tumor visualization
•
by increasing soft-tissue
contrast
Improve visualization of
vasculature which serves as a
surrogate for lymph node
location
– Time to scan: 20 min.
CT image at level of isocenter
Anatomy
• Anatomical structures contoured by the physician and
•
dosimetrist
Time to create: 60 min. for MD; 30 min. for dosimetrist.
3D rendering of target
and critical structures
Planning goals
•
•
•
1.8Gy/fraction
Total dose to target
55.8 Gy
Dose limit of critical
structures
Structure
Spinal cord
Brain stem
Parotis
Partial PTV
Limit (Gy)
45
45-50
Dmean <26
47.5-53.2
Gantry positions
• 5, 7 or 9 equally•
•
spaced, nonoverlapping fields
Coplanar, no
couch rotation
Remote gantry
rotation and Auto
Field Sequencing
decrease time
required for
treatment delivery
5 field IMRT (1000 segments) delivered
in less than 5 minutes
Treatment planning
• Setup the
•
•
beams in
Eclipse
Define dose
prescription
Select
“Optimize” to
start Helios
Dose constraints
• Example: Head and
•
•
•
•
neck
CTV
53.2<D<58
T-PTV
47.5<D<53.2
Spinal cord
D<45
Parotis
Dmean<26
Dose constraint library for class
solutions
Inverse planning
• Time to enter
•
planning goals:
2-10 min.
Begin inverse
planning.
Prepare to calculate dose
Helios returns an optimal fluence map for each beam
Leaf Motion Calculator (LMC) converts optimal map to actual fluence map
Leaf end shape
Leaf transmission
Output factors
Jaw transmission
Leaf speed
Leaf acceleration
Optimal fluence map Acutal fluence map
LMC
Isodose distributions
Isodose lines are:
50% dark blue
60% sky blue
70% teal
80% blue-green
90% green
92, 94, and 96% yellow
and orange
98% red
100% pink
Time to review a plan:
10-15 min. per plan
IMRT treatment plan for PTV1
Plan review
• Typically, start with DVH’s
– Examine target dose homogeneity
– Examine dose to critical structures
– May choose to renormalize the plan, based on DVH
analysis
• Important to review isodose distribution on
every slice
– As dose conformation increases, so does dose
heterogeneity in the target
• Look for hot spots and cold spots
– Where are they located?
– How hot/cold are they?
Treatment plan
Gantry
• MU/field are high.
• Number of
segments/field is high.
• Time to treat = 30-60
sec./field
200
240
280
320
0
40
80
120
160
This plans has more than 1000 segments and
is delivered in 7-8 minutes.
MU
58
99
83
101
112
98
74
71
112
Segments
70
122
102
148
134
142
104
94
150
Transfer to record & verify
system
• If the plan is accepted, it is transferred to
VARiS
• Electronic transfer of treatment plan details to record
and verify system.
–
–
–
Patient safety
Efficiency
With VARiS and Eclipse v6.5, there is no transfer. The
VARiS database IS the Eclipse database.
• Time to prepare record and verify system: 10-30 min.
QA of record & verify data
• After data are entered into VARiS, custom
reports are used for QA
DRRs for setup verification
• Treatment planning CT scan used to create AP and lateral
•
DRRs.
Time = 10 min.
With VARiS and Eclipse v6.5, DRRs are automatically
created and associated with treatment fields. Time = 0!
AP DRR
Lateral DRR
Independent MU check
• Software is used to
perform independent
MU check.
First day of treatment
• Patient is setup using lasers and a set of orthogonal
•
films or PV images is acquired.
To verify the setup, films/images are compared to
DRRs.
Reference images
Acquired images
Patient setup verification
First day of treatment
• If setup accuracy is critical, therapists may
decide that small adjustments would improve
the setup, make the adjustments, and then
acquire a second set of images.
• When the therapists are satisfied that the
setup is correct, attending physician can be
called for final approval.
Collision avoidance
• After the setup is approved, therapists perform a visual check of
•
treatment plan to ensure adequate clearance. Then, they leave
the treatment room and deliver the IM plan.
First day of treatment: (Setup, setup verification and correction,
treatment) 30-45 min.
Other treatment days
• If care is taken to verify the patient setup and treatment
plan on the first day, then all other days proceed quickly
and smoothly.
• Other treatment days: (Setup and treatment) 10-15 min.
Portal imaging
• Some clinics use PortalVision to verify the patient setup,
every day, before treatment.
–
–
Improves accuracy of treatment delivery
Allows smaller planning margins to be used and thus spares
normal tissue irradiation
• Most clinics use PortalVision or film only once per week
to verify the patient setup.
• Most clinics are using AP and lateral views to verify
patient setup.
IMRT QA
• Verify intensity map of each beam
• Verify delivered dose in phantoms
– Point dose measurement using ion chamber
or TLD’s
– Qualitative verification of isodose distribution
using film
Film or PV used to verify intensity
maps
Calculated by computer
Recorded on film
Recorded using PV
PV used to verify intensity maps
• PV Dosimetry provides quantitative
analysis tools
Calculated by computer
Recorded using PV
Verify dose
• Patient’s plan is projected
•
•
•
•
onto phantom.
Physicist places ion
chamber in target or critical
structure.
Or he may use TLDs or film.
The patient’s treatment
plan is delivered to the
phantom.
Ion chamber
Measured and calculated
doses are compared.
Patient’s plan cast into phantom
Results
• Ion chamber, TLD results should agree to within
•
± 3-5%
Film dosimetry results should be good, too
Calculated and measured
isodose lines
Conclusion
• IMRT is a process.
– Immobilization
– CT Simulation
– Treatment planning
– Plan review and approval
– Treatment delivery
– Portal imaging
• Precision and care required at each step.
• Careful quality assurance is essential to
IMRT.