2SimulationThe 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 shieldsA virtual workstation, equipped with a CT scanner, software to perform target volume definition and treatment planning dose calculation, and production of DRRs
3DefinitionsLocalization: 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.
4DefinitionsRadiopaque 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.
5DefinitionsSeparation (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 tumorMeasured with a caliperField size: the dimensions of a treatment field at the isocenter, represented by width x lengthDetermined by the field-defining wires
6Specific Target Volumes Gross tumor volume (GTV): indicates the gross palpable or visible tumorClinical target volume (CTV): indicates the gross palpable or visible tumor and a surrounding volume of tissue that may contain subclinical or microscopic diseasePlanning target volume (PTV): indicates the CTV plus margins for geometric uncertainties, such as patient motion, beam penumbra, and treatment setup differences.
7SimulatorPrimary function: to localize the tumor volume in three dimensionsShould 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.
8CT/MRICross-sectional information provided by CT and MRI imaging contributes considerable information to the radiation oncologist:DiagnosisTumor and normal tissue localizationTissue density data for dose calculationFollow-up treatment monitoringConventional CT: provides detailed diagnostic information used by the radiologist and radiation oncologist to evaluate the extent of the disease.
9CT 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 surfaceVirtual simulation package that generates DRRs used to evaluate and simulate the casethe target is defined first, then fields are shaped to conform to the target
10Conventional Simulation The field locations are determinedTarget is definedThe fields are shaped to treat the targetMay use fluoroscopy to initially view the areaRadiographs document what has been done during the simulation process and used as “masters” when comparing port films
11Conventional 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 treatmentRequires tumor localization in two dimensions only, because all tissues within these fields are treated and the exact depth of the tumor is not critical.
12Conventional Simulation Localization Methods SAD (isocentric technique): provides tumor localization in three dimensionsThe isocenter is placed within the target volume with the aid of fluoroscopy and other imaging modalitiesOrthogonal films taken: two radiographs taken at right angles to one another.
13ContrastVisually enhance anatomic structures that would normally be more difficult to see.Barium sulfate:not absorbed by the GI tractAdministered orally or rectallyPatient should be advised as to the use of a laxativeIodinated contrast materials:Used for kidneys, bladder, and prostate, GI when barium contraindicatedSterile procedures must be followedMay be administered intravenously or through bladder catheterizationNegative contrast agents:Carbon dioxide, oxygen, and airAppear as dark areas on a radiograph
14Conventional Simulation Procedure Presimulation planningRoom PreparationExplanation of procedurePatient positioning and immobilizationOperation of simulation controlsSetting field size parametersSelecting exposure techniqueRadiographic exposureDocumenting pertinent dataFinal Procedures
15Presimulation 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.
16Preparing the RoomProper 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
17Explanation 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 stateNervous, withdrawn, fearfulRequire oxygen, medicationDifficulty standing, sitting, walking
18Explanation of procedure Communication: therapeutic communication can establish an environment conducive to communicationIntroduce staff and explain the simulation procedure in detail and an explanation of what procedures to follow after simulation and treatmentHow to take care of skinFullness of bladderFollow-up instructions for bariumKeep the conversation directed at the patientAvoid close ended questionsFace the patient and maintain eye contact whenever possibleCheck for understanding, restate or repeatReduce unwanted noiseSpeak clearly, confidently, and at a rate and tone conducive to listening
19Explanation of procedure Observation: noting facial expressions, body gestures, space relations, and contradictions in patients communicationCultural 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 aspectsSimulation is an opportunity to educate the patient and answer questions concerning the treatment process, side effects and skin care.
20Patient PositioningPatient positioning should be communicated along with an explanation of why that position is needed- facilitates patient’s cooperationThree directional lasers are used for patient alignmentA persons age, weight, general health, and anatomic area can affect positionInk tattoos, visible skin marks, references to topographic anatomy used to delineate the areaIf 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.
21ImmobilizationImmobilization 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 reproducibilityEnsure that immobilization of the patient or treatment area is done with a minimum of discomfortAchieve the conditions prescribed in the treatment planEnhance precision of treatment with minimal additional setup timeAre rigid and durable enough to withstand an entire course of treatmentTake into consideration the patient’s condition and treatment unit limitations
22ImmobilizationPositioning aids: devices designed to place the patient in a particular position for treatmentVery little structure, widely available, easy to use, may be used for more than one patientHead holders, pillows, cushions, sandbag, L-shaped arm boardSimple immobilization: restrict some movement but usually require the patients voluntary cooperationTape, Velcro, rubber band, arm to foot strapsBite 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
24Setting 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 SADOrthogonal films, which provide three dimensional information may be used with the SAD
25Producing 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 compositionOrienting the film: grid use, fast screen?Centering the film, reducing the size of the diaphragm opening, and setting an appropriate source-film distance, collimationPhototiming: form of automatic exposure control in which one or more ionization cells automatically stop the exposure at pre-selected densityProcessing the filmDocumenting the radiographic images: information on the film
26Documenting Pertinent data Essential to accurately reproduce the geometry of the setup on the treatment unitTo maintain accurate medical recordsTo aid in the treatment planning and dose calculation processesIncludes bothMarking patientDocumentation in chart
27Documenting Pertinent data IFD: directly influences the dose to both the tumor and other normal tissuesUsing 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 landmarksA resimulation is not required if the skin marks are lostThe treatment field can be easily reconstructed ling after the current course of therapy.
28ContoursContour: a reproduction of an external body shape, usually taken through the transverse plane of the CA of the treatment beamProvides 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
29Types of Contours Material/Method Advantages Disadvantages Solder Wire Reusability, pliabilityPliability (distortions)Plaster stripsInexpensive, transferability of surface ink markingsDrying time, messy, not reusableAquaplast contour tubesInexpensive, reusable, shapes wellDrying time, not well suited for intricate areasPantograph contouring deviceTime-saving operation, reproduces detail wellCost, size, storage space requiredCTAccurate transverse viewsCost of interfaceMRIAccurate transverse, coronal, and sagittal contoursUltrasoundDiscernable transverse correlation of internal structuresPoor quality of imaged deep structures
30Record 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