Simulation Procedures

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Chapter 20

• Simulation Procedures

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Simulation

• The success of treatment is directly related to
  the effectiveness of the simulation procedure.
• Helps in determining the location and extent of
  disease relative to adjacent critical normal
  tissues.
• The precise mockup of a patient treatment may
  include
• The selection of immobilization devices,
  radiographic documentation of treatment ports,
  measurement of the patient, construction of
  patient contours, and shaping of fields.
• Artificially duplicates the actual treatment
  conditions by confirming measurements, verifying
  treatment, and confirming shields
• A virtual workstation, equipped with a CT
  scanner, software to perform target volume
  definition and treatment planning dose
  calculation, and production of DRRs

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Definitions

• Localization geometrical definition of the
  position and extent of the tumor or anatomic
  structures by reference of surface marks that can
  be used for treatment setup purposes.
• Verification a final check that each of the
  planned treatment beams does cover the tumor or
  target volume and does not irradiate critical
  normal structures.

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Definitions

• Radiopaque marker a material with a high atomic
  number (lead, copper, or solder wire) used on the
  surface of a patient or placed in a body cavity
  to delineate special points of interest for
  calculation purposes or to mark critical
  structures requiring visualization during
  treatment planning, often used to mark specific
  points on a patient during the CT acquisition.

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Definitions

• Separation (intrafield distance IFD) the
  measurement of the thickness of a patient along
  the central axis or at any other specified point
  within the irradiated volume.
• Helpful in calculating the amount of tissue in
  front of, behind, or around a tumor
• Measured with a caliper
• Field size the dimensions of a treatment field
  at the isocenter, represented by width x length
• Determined by the field-defining wires

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Specific Target Volumes

• Gross tumor volume (GTV) indicates the gross
  palpable or visible tumor
• Clinical target volume (CTV) indicates the gross
  palpable or visible tumor and a surrounding
  volume of tissue that may contain subclinical or
  microscopic disease
• Planning target volume (PTV) indicates the CTV
  plus margins for geometric uncertainties, such as
  patient motion, beam penumbra, and treatment
  setup differences.

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Simulator

• Primary function to localize the tumor volume in
  three dimensions
• Should define the anatomic area so that it is
  reproducible for daily treatment.
• The location of a treatment field during
  simulation must reflect precisely what will
  happen in the treatment room.

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CT/MRI

• Cross-sectional information provided by CT and
  MRI imaging contributes considerable information
  to the radiation oncologist
• Diagnosis
• Tumor and normal tissue localization
• Tissue density data for dose calculation
• Follow-up treatment monitoring
• Conventional CT provides detailed diagnostic
  information used by the radiologist and radiation
  oncologist to evaluate the extent of the disease.
  

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CT Simulation

• No image receptor such as film or image
  intensifier,
• A collimated x-ray beam is directed at the
  patient, and the attenuated beam is measured by a
  detector whose response is transmitted to a
  computer.
• The computer analyzes the signal from the
  detector, reconstructs the image and then stores
  and/or displays the image.
• Components of a CT simulator workstation
• Target localization routine that allows the
  target to be defined and transfers the
  appropriate mark to the patient skin surface
• Virtual simulation package that generates DRRs
  used to evaluate and simulate the case
• the target is defined first, then fields are
  shaped to conform to the target

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Conventional Simulation

• The field locations are determined
• Target is defined
• The fields are shaped to treat the target
• May use fluoroscopy to initially view the area
• Radiographs document what has been done during
  the simulation process and used as masters when
  comparing port films

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Conventional Simulation Localization Methods

• SSD positions a fixed treatment distance of 80
  or 100 cm on the patients skin for each field.
• Requires repositioning the patient for each field
  before treatment.
• usually single field, two laterals or an AP/PA
  treatment
• Requires tumor localization in two dimensions
  only, because all tissues within these fields are
  treated and the exact depth of the tumor is not
  critical.

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Conventional Simulation Localization Methods

• SAD (isocentric technique) provides tumor
  localization in three dimensions
• The isocenter is placed within the target volume
  with the aid of fluoroscopy and other imaging
  modalities
• Orthogonal films taken two radiographs taken at
  right angles to one another.

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Contrast

• Visually enhance anatomic structures that would
  normally be more difficult to see.
• Barium sulfate
• not absorbed by the GI tract
• Administered orally or rectally
• Patient should be advised as to the use of a
  laxative
• Iodinated contrast materials
• Used for kidneys, bladder, and prostate, GI when
  barium contraindicated
• Sterile procedures must be followed
• May be administered intravenously or through
  bladder catheterization
• Negative contrast agents
• Carbon dioxide, oxygen, and air
• Appear as dark areas on a radiograph

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Conventional Simulation Procedure

1. Presimulation planning
2. Room Preparation
3. Explanation of procedure
4. Patient positioning and immobilization
5. Operation of simulation controls
6. Setting field size parameters
7. Selecting exposure technique
8. Radiographic exposure
9. Documenting pertinent data
10. Final Procedures

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Presimulation Planning

• An assessment of all relevant patient information
  and an evaluation of possible treatment
  approached before the patient arrives.
• Minimally, the patients history and physical
  examination notes should be reviewed, other
  available information (CT, X-rays, pathology
  reports and operating reports)
• The preparation of specialized immobilization
  devices.

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Preparing the Room

• Proper room preparation can aid in the effective
  use of simulator time.
• Sanitize materials used from previous patient.
  
• Clean cloth or paper sheet placed on simulator
  couch.
• Anticipated immobilization devices prepared and
  ready

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Explanation of procedure

• Assessment assess patients needs, cultural
  differences, nonverbal communication, and then
  attempt to communicate therapeutically and
  effectively with the patient.
• Physical condition and emotional state
• Nervous, withdrawn, fearful
• Require oxygen, medication
• Difficulty standing, sitting, walking

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Explanation of procedure

• Communication therapeutic communication can
  establish an environment conducive to
  communication
• Introduce staff and explain the simulation
  procedure in detail and an explanation of what
  procedures to follow after simulation and
  treatment
• How to take care of skin
• Fullness of bladder
• Follow-up instructions for barium
• Keep the conversation directed at the patient
• Avoid close ended questions
• Face the patient and maintain eye contact
  whenever possible
• Check for understanding, restate or repeat
• Reduce unwanted noise
• Speak clearly, confidently, and at a rate and
  tone conducive to listening

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Explanation of procedure

• Observation noting facial expressions, body
  gestures, space relations, and contradictions in
  patients communication
• Cultural diversity be aware of cultural
  differences in both verbal and nonverbal
  communication to avoid being misunderstood,
  offending someone, or being offended by someone.
• Educating the patient and family about the
  physical aspects of radiation therapy but also
  the emotional aspects
• Simulation is an opportunity to educate the
  patient and answer questions concerning the
  treatment process, side effects and skin care.

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Patient Positioning

• Patient positioning should be communicated along
  with an explanation of why that position is
  needed- facilitates patients cooperation
• Three directional lasers are used for patient
  alignment
• A persons age, weight, general health, and
  anatomic area can affect position
• Ink tattoos, visible skin marks, references to
  topographic anatomy used to delineate the area
• If a CT scan is performed on a conventional CT,
  the therapist must accompany the patient to
  ensure the patient is in the same treatment
  position when scanned.

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Immobilization

• Immobilization is used to achieve true
  reproducibility and accuracy.
• Once the threshold dose for tumor response has
  been reached, small increases in the absorbed
  dose may make large differences in tumor control.
• Once the threshold for normal tissue injury has
  been reached, small increases in dose may greatly
  increase the risk of complications.
• Effective immobilization devices
• Aid in daily treatment setup and provide
  reproducibility
• Ensure that immobilization of the patient or
  treatment area is done with a minimum of
  discomfort
• Achieve the conditions prescribed in the
  treatment plan
• Enhance precision of treatment with minimal
  additional setup time
• Are rigid and durable enough to withstand an
  entire course of treatment
• Take into consideration the patients condition
  and treatment unit limitations

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Immobilization

• Positioning aids devices designed to place the
  patient in a particular position for treatment
• Very little structure, widely available, easy to
  use, may be used for more than one patient
• Head holders, pillows, cushions, sandbag,
  L-shaped arm board
• Simple immobilization restrict some movement but
  usually require the patients voluntary
  cooperation
• Tape, Velcro, rubber band, arm to foot straps
• Bite block helps the patient maintain the
  position of the chin, and moves the tongue out of
  the treatment field.
• Complex immobilization are individualized
  immobilizers that restrict patient movement
  (plaster, plastic, Styrofoam)
• Vac-loc, foaming agents, aquaplast

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Operating Controls

• Mechanical components gantry rotation,
  collimator movements, treatment couch
• Optical components laser system, optical
  distance indicator (ODI), field light indicator
• Radiographic components kVp, mAs

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Setting Field Parameters

• Field parameters such as width, length, gantry
  angle, collimator angle, and position of the
  isocenter should be established for both the SSD
  and SAD setup.
• The isocenter is positioned at the CA on the
  patients skin for an SSD approach and within the
  patient for SAD
• Orthogonal films, which provide three dimensional
  information may be used with the SAD

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Producing Quality Images

• Selecting exposure technique vary from one
  clinical site to the next and from one simulator
  to another.
• Body habitus attenuation of the x-rays will
  vary, depending on the patients thickness and ,
  to a lesser degree to the bodys composition
• Orienting the film grid use, fast screen?
• Centering the film, reducing the size of the
  diaphragm opening, and setting an appropriate
  source-film distance, collimation
• Phototiming form of automatic exposure control
  in which one or more ionization cells
  automatically stop the exposure at pre-selected
  density
• Processing the film
• Documenting the radiographic images information
  on the film

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Documenting Pertinent data

• Essential to accurately reproduce the geometry of
  the setup on the treatment unit
• To maintain accurate medical records
• To aid in the treatment planning and dose
  calculation processes
• Includes both
• Marking patient
• Documentation in chart

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Documenting Pertinent data

• IFD directly influences the dose to both the
  tumor and other normal tissues
• Using bony landmarks as reference has advantages
• Skin marks are highly mobile, especially for
  obese patients, whereas the location of the
  target volume remains essentially constant with
  respect to bony landmarks
• A resimulation is not required if the skin marks
  are lost
• The treatment field can be easily reconstructed
  ling after the current course of therapy.

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Contours

• Contour a reproduction of an external body
  shape, usually taken through the transverse plane
  of the CA of the treatment beam
• Provides the therapist and dosimetrist with the
  most precise replica of the patients body shape
  so that accurate information may e gathered
  concerning the dose distribution within the
  patient.
• The treatment volume and internal structures are
  transposed within the contour using data from the
  simulation images and/or CT or MRI films.
• Assists in repositioning the patient

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Types of Contours
Material/Method Advantages Disadvantages
Solder Wire Reusability, pliability Pliability (distortions)
Plaster strips Inexpensive, transferability of surface ink markings Drying time, messy, not reusable
Aquaplast contour tubes Inexpensive, reusable, shapes well Drying time, not well suited for intricate areas
Pantograph contouring device Time-saving operation, reproduces detail well Cost, size, storage space required
CT Accurate transverse views Cost of interface
MRI Accurate transverse, coronal, and sagittal contours Cost of interface
Ultrasound Discernable transverse correlation of internal structures Poor quality of imaged deep structures
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Record and verify systems

• Tolerances may be set on many of the treatment
  units positions, such as couch height and couch
  positions in the left/right and inferior/superior
  direction