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Simulation Procedures

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1 Simulation Procedures
Chapter 20 Simulation Procedures

2 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

3 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.

4 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.

5 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

6 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.

7 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.

8 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.

9 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

10 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

11 Conventional Simulation Localization Methods
SSD: positions a fixed treatment distance of 80 or 100 cm on the patient’s 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.

12 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.

13 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

14 Conventional Simulation Procedure
Presimulation planning Room Preparation Explanation of procedure Patient positioning and immobilization Operation of simulation controls Setting field size parameters Selecting exposure technique Radiographic exposure Documenting pertinent data Final Procedures

15 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.

16 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

17 Explanation of procedure
Assessment: assess patient’s 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

18 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

19 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.

20 Patient Positioning Patient positioning should be communicated along with an explanation of why that position is needed- facilitates patient’s 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.

21 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 patient’s condition and treatment unit limitations

22 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

23 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

24 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

25 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 body’s 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

26 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

27 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.

28 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

29 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 Ultrasound Discernable transverse correlation of internal structures Poor quality of imaged deep structures

30 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

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