Chapter 20

1. 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

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