Treatment verification and set up errors

1
Sailakshmi.P
MSc Radiation Physics
Calicut University

IN SLIDES
 Importance of Treatment Verification
 Treatment Verification
 Machine set-up
 Monitor units and dose
 Patient positioning and imaging
 Process of Treatment Verification
 Set-Up Error
 Systematic error
 Random error
 To Reduce the Treatment Errors
2

IMPORTANCE OF TREATMENT VERIFICATION
 All radiotherapy involves risk because even a small error in treatment
Planning, Delivery, or Dosimetry can lead to negative consequences.
 This is because the human body is a complex organism and tumors are
often located in close proximity to sensitive normal tissues and critical
organs.
 So this process enables us to be certain that, we are treating the tumor
volume as planned.
 In ensuring that the right radiation dose has been given to the right
place .
3

TREATMENT VERIFICATION
 Machine set-up (including table)
 Monitor units and dose
 Patient position and imaging (image comparison)
4

MONITOR UNITS AND DOSE
 MUs represent a special case of machine set-up parameters because they are
permanently increasing during beam delivery.
 Prescribed MUs must be delivered during the treatment.
 If the prescribed number of MUs has been delivered, the beam must be
terminated. In case the beam is terminated prior to delivery of the requested
number of MUs, the actually delivered number of MUs should be recorded.
 The missing number of MUs might be automatically displayed and delivered
subsequently, after the problem causing the treatment interruption has been
solved.
5

MACHINE SET UP
 Machine set-up should be consistent with the treatment parameters
specified during treatment planning or simulation.
 Machine set-up parameters that are usually verified include beam
quality, beam energy, field size and leaf settings, collimator and gantry
angles, presence of beam modifiers, table position and table angle.
 If there is any variation to these parameters that should be within the
tolerance limit.
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PATIENT POSITION AND IMAGING
(IMAGE COMPARISON)
 Verification of the patient’s position is partly achieved via table coordinates
including the table angles.
 Table angle and vertical position can be verified for all patients, but accurate
verification of longitudinal and lateral table positions requires the application of
immobilization devices.
 Table coordinates of the first session serve as the standard for all subsequent
sessions.
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PATIENT POSITION AND IMAGING
(IMAGE COMPARISON)
 In the light of advanced radiotherapy techniques, accurate verification of the
patient’s position is essential.
 This requires that images(e.g. portal images or volumetric image information)
are frequently acquired throughout the treatment to verify and correct patient
set-up.
 It is common practice to compare or register ‘images of the day’ with reference
images and to calculate translation and rotation displacements to be applied to
the table parameters to correct the patient set-up.
 With modern radiotherapy equipment, set-up corrections might be performed
automatically from the treatment console.
8

AN EXAMPLE OF A TYPICAL FLOW CHART FOR THE
PROCESS OF TREATMENT VERIFICATION
PRETREATMENT
Acquire Reference Image
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Acquire treatment images
#1
#2
#3
Error
level
above
action
?
Continue with current set
up
Review image against ref.
YesNo
STOP
Revise set up & re-image
Calculate mean displacement
in all 3 axes
Error
level
above
action?
up
Adjust set up
Re-image for at least next
2#
No Yes
10

#4 No imaging
Acquire treatment
images
#5 No imaging
Acquire treatment
images
Error
level
above
action?
up
STOP
Investigate further
Review image
against ref.
No Yes
Calculate mean displacement
for 2 images in all 3 axes
Acquire treatment
images
weekly
Out of
tolerance
?
up
STOP
Investigate further
No Yes
11

SET-UP ERROR
 It is used to describe the discrepancy between intended and actual
treatment position.
 Normally calculated as a shift in treatment field position when a treatment
image is compared against it corresponding reference.
 It may be determined relative to the isocenter, the field borders or both.
 It comprises a Systematic and Random error.
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SYSTEMATIC ERROR
 Systematic component of any error is a deviation that occurs in the same direction
and similar magnitude for each # throughout the treatment course.
 Systematic errors may be introduced into patient treatment at the localisation,
planning or treatment delivery phases.
 For this reasons these type of errors are referred to as treatment preparation
errors.
 Once frozen into the process, systematic error will occurs in each treatment
fraction.
14

SYSTEMATIC ERROR
 Generally introduced at planning and therefore propagated
throughout treatment.
 Patients movement during CT scan.
 Interobserver variability in contouring.
 Jaws/MLCs in wrong position.
 planning and treating the wrong site.
15

RANDOM ERROR
 The random component of any error is a deviation that can vary in
direction and magnitude for each delivered treatment fraction.
 Random errors occurs at the treatment delivery stage and for this reason
are often referred to as treatment or daily execution errors.
 Daily variable movements – internal and external!
 Mis interpreting set-up instructions.
 Poorly immobilised patients.
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TO REDUCE TREATMENT ERRORS….
 After the diagnosis of CA take the images accurately using immobilisations
(if needed). (CT simulator /simulator used for imaging purpose)
 Then the Doctors would draw GTV, PTV ,CTV and OARs according to the
protocol using CT images.
 After contouring, Medical Physicist would plan the treatment perfectly
understanding the situation.
 The produced plan need to be checked and verified by Physicist and
Doctors.
 Only after the double verification send the optimal plan to the console.
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TO REDUCE TREATMENT ERRORS….
 Before setting the patient conform the patient name and RT number .
 In the console the Technologist should be set the machine and patient as
per the plan by the help of reference image with MV/kV image.
 If there is any machine set-up error or patient set up error occurs that
should be within the tolerance limit otherwise investigate and solve the
problem before treatment delivery.
 And follow the above mentioned (flow chart procedure) way of treatment
verification.
 To reduce the machine errors the Quality Assurance of the machine should
be verified by the Medical Physicist as per QA protocol.
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Nothing Is Completely Perfect…..!
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REFERENCES
• On target: ensuring geometric accuracy in radiotherapy by IPEM
• Record and Verify Systems for Radiation Treatment of Cancer : Acceptance
Testing, Commissioning and Quality Control, Human Health Report No 7 by
IAEA.
• Measurement and detection of radiation by Nicholas.
• Physics of Radiation Therapy by F M Khan.
• Prescribing , Recording and Reporting Photon Beam Therapy, ICRU 62.
• The importance of accurate treatment planning, delivery, and dose
verification by Julian Malicki.
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Treatment verification and set up errors

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