Sim Procedures Lecture 2

1
Sim Procedures Lecture 2

• Elizabeth Small B.S.R.T.T.

2
Considerations

• Factors that can affect patients position
• Age
• Weight
• General health
• Anatomical area

3
Reference Marks

• Delineate Treatment Area
• India ink tattoos
• Sharpie-marker
• Use of topical anatomy
• Sternal Notch
• Xiphoid Tip
• Iliac Crests
• Mentum
• EAM
• Symphysis Pubis

4
Positioning Errors

• Immobilization Devices- maintain patient position
• Increase accuracy
• Increase reproducibility
• One or two patient positioning errors can
  possibly cause the tumor volume to be missed.
• Tumor dose can be reduced by 10

5
Simulator Controls

• Mechanical components
• Gantry
• Collimator
• PSA
• Optical components
• Laser system
• ODI
• Field light indicator

6
Simulator Controls

• Radiographic controls
• State regulations require the use of technique
  charts
• Guidelines
• kVp, mA, and time exposure factors
• Some departments have Sim Therapists

7
Sim Issues

• ODI light bulb burns out
• Mechanical limits
• Radiographic exposure limits

8
Setting Field Parameters

• Familiarity with the controls
• Efficient
• Smooth
• Accurate
• Field Parameters necessary for both SSD and SAD
  setups
• Field width, length, gantry angle, collimator
  angle, isocenter

9
Setting Field Parameters

• Starting point
• Put iso in area of interest
• SSD iso
• SAD iso within body - most setups
• Field size can be set (X and Y)
• Straighten the patient
• Precise with fluoroscopy
• Orthogonal films- define the isocenter in 3
  dimensions

10
Setting Field Parameters

• Next Step Depends
• Simple setup
• Complex
• CT info
• V-sim
• DRRs
• Radiographs
• More complex - more time required
• Tattoo??
• Documentation is critical

11
Producing Quality Radiographs

• Radiographs
• Ortho set-
• may or may not be a treatment field
• Document the treatment field
• All treatment fields should be filmed if possible
• Part of the medical record
• Used as master to compare port films taken on the
  unit

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Producing Quality Radiographs

• Exposure Factors
• 5 main factors
• kVp
• mA
• Time
• Distance
• Patient body habitus

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Producing Quality Radiographs

• Attenuation of x-rays varies depending
• Patient thickness
• Body composition
• Disease processes
• Pneumonia or CHF - increase exposure
• Emphysema and osteoporosis - decrease exposure

14
Producing Quality Radiographs

• Film considerations
• Centering the film
• Size of diaphragm opening
• SFD - 140 cm common

15
Producing Quality Radiographs

• Phototiming
• AEC-automatic exposure control-preprogrammed
  density
• Anatomically programmed radiography- computerized
  technique charts- pick body type
• These provide more consistency of radiographs
  with appropriate contrast and density

16
Mechanical Issues

• Know where emergency off buttons are
• Know where the circuit breaker is
• Controls power to mechanical components and x-ray
  generator
• Anti-collision devices
• Collimator
• Delcalix (delc) - image intensifier

17
Film Processor

• Requires quality control
• Chemicals filled and right mixtures
• Some departments
• Weekly cleaning/processing
• Outside company
• Therapists responsibilities

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Radiograph-Information

• Pertinent info
• Name
• Date
• Field-AP/PA, Lt Lat
• SSD
• MTH
• Shifts from Iso
• Field size (f.s.)
• Gantry angle/Collimator angle
• SFD
• Therapists Initials
• Machine
• Physician/resident
• Physicians Signature

19
Documentation of Pertinent Info

• Documentation
• Why????
• Worksheets used
• Designed to include info necessary to setup the
  patient
• Address all the setup parameters
• See pg 455

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Important Parameters

• IFD
• Intrafield distance (separation)
• Directly influences the dose to the tumor and
  other normal tissues
• Correct caliper use is critical
• Measures patient thickness
• Flat area- need only one measurement
• Sloped surface multiple measurements

21
Identifying Location of Treatment Fields

• Two schools of thought
• 1. External marks
• Tattoos- India ink, small gauge needle, (1mm in
  size is better than skin marks)
• Sharpie, carfusion (silver nitrate)
• sticker Xs
• 2. References bony landmarks
• Ca and field edges referenced to anatomical
  landmarks or scars
• EAM, Gonion, SN, SOM, IOM, IC, OC, tragus,
  commissure of the mouth, mastoid process, xiphoid
  tip

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Advantages of Using Anatomical Landmarks

• 1. Skin marks highly mobile, whereas bony anatomy
  is not
• Obese pts
• Wt loss
• Tumor shrinkage
• 2. No resim necessary if skin marks lost
• 3. Tx field easily reconstructed later time

23
Contours

• Purpose
• Necessary to properly calculate the dose to the
  area
• Accounts for the patients anatomy from any
  treatment angle
• What is a contour?
• An external representation of the patients shape
• Who gets the contour?
• Therapist, dosimetrist, physics
• Questions about where to contour?
• Ask Dosimetrist, physician, physics

24
Contours

• A contour is usually the last step in a clinical
  sim
• Breast
• Rectum
• Larynx
• H N
• CTs have replaced all of the conventional
  contours
• Simulate when in sim
• Plaster of Paris
• Solder wire
• Rods
• Pantograph

25
Treatment Verification

• Another simulation
• Used to be done for all CT planned cases
• CT Sims have changed this
• Sims are all done in one step now

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Treatment Verification

• Almost all verification occurs on the treatment
  units first day
• Blocks or MLCs checked on treatment unit when
  films are taken

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Treatment Verification

• Dosimetry will use info from the CT(or MRI) scan
• Come up with moves based on the reference when
  CTed (identified by placing CT catheters on skin
  to designate the reference point)
• All tx info- gantry angle, f. s., has been
  determined
• The treatment plan is complete
• BEV plots created
• Critical anatomy
• Treatment volume identified
• SFD is important when filming V-sim

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Treatment Verification

• Therapist will
• Review all info on the plan
• Review patient position
• Must be setup exactly like was CTed
• Review and make moves to be made-establish
  isocenter where tattoos will be placed
• SSD to set
• Proceed to set parameters
• Get a good ortho set first
• Dosimetry will check films

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Treatment Verification

• Each treatment field
• Will be setup- gantry, collimator, f.s, pedestal
• Filmed
• at correct SFD (BEV plot will have SFD on it)
• Exposure factors set
• Shutters open
• Delc centered (sometimes necessary to offset it
  to get treatment field)
• Must show all field edges
• Pertinent anatomy must be visible

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Treatment Verification

• SSD taken
• Film compared to BEV
• More moves may be made and redo filming
• Keep doing until films match BEVS
• Get a good orthogonal set first, then go on to
  film all treatment fields
• The V-sim films will be compared to the treatment
  ports taken on the units
• Tattoo, documentation
• Verify all components in chart

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Emergencies in Sim

• What are they???
• Anaphylactic shock
• Crash Cart location
• Emergency kit
• CPR
• Call a CODE- know numbers to call

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Sim

• Treatments are directly affected by the
  simulation process
• Good sim
• Allows for accurate setup
• Reproducible setup
• Patient will be reasonably comfortable

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Final Steps- Sim

• Getting the patient up
• Verifying next appointment day/time
• Restating that daily treatment times will be
  setup by the therapist on the machines
• What to do when they come in
• Checking in, family, wear to change and wait, etc.

34
Final Steps-Sim

• How to dress if no changing needed
• Assure them that they can eat before
• Bladder empty, full or other instructions
• Length of time start- one hr typically
• Give phone numbers
• Introduce to machine therapists
• Skin care, nothing on for tx
• Return them to their family

35
Questions

• The device that projects a scale onto the
  patients skin, corresponding to the SSD is called
  what?
• A. PSA
• B. Gantry
• C. ODI
• D. Collimator Assembly

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Questions

• 2. To control scatter radiation during
  fluoroscopy the _________should be adjusted.
• Isocenter
• PSA
• Field defining wires
• Beam restricting diaphragm

37
Questions

• 3. All of the following are optical devices used
  during the sim process except
• A. Patient table top
• B. ODI
• C. Light field
• D. Lasers

38
Questions

• 4. The accessory holder on the simulator may
  serve which of the following purposes?
• I. Function as an electron cone adapter
• II. Simulate custom block verification
• III. Absorb scatter radiation from thicker body
  parts
• IV. Provide scanning movements for the imaging
  system
• A. I and II only
• B. I and III only
• C. II and IV only
• D. I-IV

39
Questions

• 5. Which of the following factors are not taken
  into consideration when determining shielding
  requirements for a simulator?
• A. Use factor(U)
• B. Occupancy factor (T)
• C. Workload (W)
• D. Inverse scattering intensity (I)

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Questions

• Which of the following involve three-dimensional
  treatment planning?
• I. Virtual simulation
• II. AP radiographs
• III. CT simulators
• IV. Portal radiographs
• A. I and II only
• B. I and III only
• C. II and III only
• D. II and IV only