Simulation Lecture, Lab, Block Cutting (ch21) REVIEW

Primary Purposes of Simulation

•Place patient in appropriate treatment position for area being planned and treated

•Assist the physician in the treatment planning process

•Establish and document appropriate volume to be treated

•Identifying the normal structures within or adjacent to the tumor volume

•Preliminary procedure of a patient treatment with radiographic documentation of the treatment portals

What is a CT Simulator?

•Dedicated CT scanner used for Radiotherapy treatment planning.

•CT Scanner is used to acquire a volumetric CT Scan of a patient which gives the “virtual” or digital information of the patient.

•CT simulation software provides virtual representation of the geometric capabilities of the treatment machine.

CT Simulation Components

1 Gantry

2.  Bore aperture

3.  Table/couch (table is made of carbon fiber)

4.  Controls

5.  Scanner lasers

6.  LAP lasers (external lasers)

7.  Remote control console and monitors

8.  Virtual simulation/focal workstation (isocenter- where the doctor wants the beam to hit)

CT Simulation External Components

1.  Couch Movement Controls

2.  Emergency Off

3.  Localizing Lasers

CT Workstation Console

1.Multiple monitors and controls for CT

•Patient data and info for each scan

•View and manipulate the reconstructed images before storing or transferring to virtual workstation

2.Virtual Workstation

•Ability to set isocenter for treatment field

3.Hardware necessary to produce high qualityDRRs (digitally reconstructed radiographs)

CT Simulator Data Acquisition

A. Axial

•Utilizes a fan-shaped beam

•Patient stays in a fixed position

•Tube rotates 360 degrees to capture a single transverse image

B. Spiral/Helical

•Involves volumetric scanning

•Captures more anatomy in the same timeframe

Reduces imaging duration

Helical scanning lessens the possibility of skipped anatomic data collection. (better for rad therapy)

Images may be visualized in any anatomic plane; axial, coronal, or sagittal

Axial Scanning

•Fan like beam (loaf of bread)

•Patient remains at a fixed point

•Tube rotates 360 degrees and collects a single image in the transverse plane

Spiral/Helical CT Simulator

•Volumetric scanning

•More anatomy included in same amount of time

•Shorter imaging times ( so better for patients in pain or that have breathing instructions)

Continual Scanning

•Continual scanning and movement of table

•

Tube rotates continuously as patient moves through the scanner “slinky or coil effect

Pitch 

is the distance the table moves between each slice.

is usually identified in departmental protocol

CT Laser

mounted on walls and ceilings of sim and tx rooms assist in localization.  Lasers converge at the point of SAD or isocenter.

Patient marks are placed on the laser light to indicate where the iso is located.

Move in three different ways

XYZ COORDINATE SYSTEM

X – Sagittal axis separates right to left in the patient
Y – Transverse axis separating head to foot in the patient

Z – Coronal axis separating  anterior/posterior in the patient

USED IN SIM

X

Sagittal (right to left)

Y

transverse (separates head to foot in patient)

z

coronal (separates anterior/posterior)

localization

Delineation of the tx target and the placement of the isocenter relative to the target is referred to as

Delineation=the act of clearly describing, drawing, or setting the boundaries of something

Marking the Patient

The isocenter marks and leveling marks must be recorded for reproducibility on the linear accelerator

Image reconstruction and Isocenter placement

•Check on patient

•Remind them to remain still

•Waiting for the physician to look over scan and place isocenter

•Information is then sent to LAP lasers

•Physician has selected the isocenter

•LAP lasers will shift to isocenter position in Sagittal(X) and Coronal planes(Z)

•Transverse plane (Y)

•Given a number to shift the table in or out

Laser Assisted Positioning (LAP)

Contrast Media & It’s Purpose

•Enhance the visibility of internal tissues for imaging

•Highlight abnormality

•Use Iodine, Barium or Air

•Oncologist depend on these agents to pinpoint target areas for radiation treatment planning

Patient History

Accurate patient history before administration of contrast is extremely important

•Name/Date of Birth

•LMP (Must be within 30 days)

•NPO status

•Past Medical History

ØDiabetes

o? Insulin

•Past Contrast Allergy

ØIs the Patient allergic to Iodine?

•Recent Labs

ØBUN (normal range 7 – 20 mg/dl)

ØCreatinine (normal range 0.5 - 1.2 mg/ dl)

Additional questions that may be asked

Prior surgery history

Prior history of cancer, recent chemo

 Prior CT scans

Personal History of Renal Disease

ØChronic Kidney Disease (CKD)

ØHistory of Acute Kidney Injury (AKI)

ØPrior renal surgery / ablation

ØDialysis

Intravenous Contrast Sample Questionnaire

1. Have you ever received iodinated contrast media before?

2. Have you ever had a reaction to iodinated contrast media?

3. Do you have any allergies to food or medications?

4. Do you have any of the following conditions?

• Allergies (Have you had an allergic reaction to contrast in the past?)

• Asthma • Kidney problems  • Cardiac disease 

• Diabetes • High blood pressure • Sickle cell anemia

• Multiple myeloma • Pheochromocytoma

5. Is there any chance you are pregnant?

6. Have you had anything to eat or drink within the last 4 hours?

•Radiolucent-Negative Contrast Agent

•Low atomic number (Z) (radiolucent)

•Easily penetrated by x-rays

•Areas affected by contrast appear dark on CT scan

•Radiopaque-Positive Contrast Agent

•High atomic number (Z) (shows up white, radiopaque)

•Absorb x-rays

•Areas affected by contrast appear white on CT scan

•Create star artifacts on the CT scans

Atomic Number (Z)

•

•Based on the number of protons in the nucleus

•Higher the Z number-the more likely it is to absorb x-rays during CT scan

•High-atomic number contrast media can create star artifacts on the CT scans

•Oral (barium)

•Intracavitary (Rectally) (barium)

•

•Intravenous (IV) (omnipaque)

Contrast Media Administration used in Radiation Therapy

GI Tract Contrast

•Barium Sulfate

•not water soluble

•Most commonly used contrast agent for GI tract exams

•Delivered Orally & Rectally in a water-based suspension

•Coats lining of alimentary organs

•High atomic number Z=56

•Generates high level of contrast

•Low solubility protects the patients from absorbing harmful amounts of metal

•

•Gastrograffin-water soluble

patients with a high risk of gastrointestinal perforation would not receive barium sulfate and instead would receive an aqueous iodinated agent such Gastrograffin

Heavy Metal Salt

•Barium Sulfate

•Most commonly used contrast agent for GI tract exams

•Delivered Orally & Rectally in a water-based suspension

•Coats lining of alimentary organs

•High atomic number Z=56

•Generates high level of contrast

•Low solubility protects the patients from absorbing harmful amounts of metal

Barium Patient History Factors

Factor	Importance
Age	Ability to communicate, hear, and follow directions ↑Risk of colon perforation caused by loss of tissue tone
Diverticulitis or ulcerative colitis	↑Difficulty in holding an enema ↑Risk of colon perforation
Long-term steroid therapy	↑Risk of colon perforation
Colon biopsy within previous 2 weeks	Lower gastrointestinal series contraindicated
Mental retardation, confusion, or dizziness	↑Risk of aspiration during upper gastrointestinal series
Recent onset of constipation or diarrhea	↑Risk of colon perforation or tumor rupture
Nausea and vomiting	↑Risk of aspiration during upper gastrointestinal series

Intravenous Contrast

Iodine

High atomic number (Z=53)

Absorb x-rays

Appear light gray to white on CT scan

Generally viscous, esp at room temperature

Injected using power injector

Proven to be one of the best contrast elements for imaging

Typically classified based on their chemical composition and influence of osmotic activity

Toxic to Kidneys

Iodine-based contrast materials are typically injected into a vein (IV)

Enhance the visualization of vascular organs and structures

Typically classified based on their chemical composition and influence of osmotic activity

Osmolality

measure of total number of particles in solution per kilogram of water

a low osmolatiry such as nonionic iodine decreases risk of side effects

Power Injector

Dual Syringe Injector

•Accurate injection of contrast and saline

•Offers various injection rates

•PSI (pounds per square inch)

•Measurements for patient safety

•300 psi pressure limit

Power Injector Steps

. Check to be sure the patient questionnaire was completed. Note any precautions as stated by the therapist, nurse or physician.

2. Have an anaphylactic kit on hand.

3. Retrieve appropriate contrast media from warmer.

4. Check expiration date of contrast to be injected. Do not use if expired.

5. Place syringe in power injector according to manufacturer specifications.

  a. Remove covering of syringe. The tip of the syringe is sterile. Connect tubing to syringe by using sterile technique.

  b. Remove air in syringe and intravenous line.

  c. Connect to patient's intravenous site.

6Position and immobilize patient.

  a. Select protocol for rate and amount of contrast to be injected. These are often predetermined based on the protocol for the department.

  b. If a smaller needle was used in the patient, the rate of administration is decreased.

7. Prepare scanner. Do not begin scan yet.

8. Begin power injection.

  a. Depending on what needs to be visualized, the scan will begin as dictated by the physician.

  b. Some departments will not inject the contrast unless a physician or nurse is present.

Patient Prep for contrast

•May include

•Fasting

•Enemas

•Compliance

•Helps lead to diagnostic-quality images with least amount of contrast media possible

Contrast Reactions

Minor, Moderate, Severe

Minor Contrast Reaction

Resolve without any intervention

•Urticaria (hives)

•Limited swelling/edema

•Limited “itchy/scratchy” throat

•Nausea

•Retching

•Mild Vomiting

Moderate Contrast Reaction

More pronounced and require intervention

Fainting

Chest pain

Abdominal pain

Headache

Chills

Sever vomiting

Dyspnea (difficult breathing)

Extensive urticaria

Edema (swelling) of face and or larynx

Severe Contrast reaction

Life-threatening if not managed appropriately

Syncope (fainting)

Convulsions

Pulmonary edema

Life-threatening cardiac arrhythmias

Cardiac or respiratory arrest

Important points to remember:

• Have patients complete a questionnaire to identify any risk of a reaction to contrast

• Ensure patients have fasted if necessary

• Perform a CT scan without contrast and complete again with contrast for treatment planning purposes

Positioning Aids

•Very little structure with design

•Not Custom for patient

•Immobilize patient to prevent as much voluntary movement as possible

•Increases comfort but does not ensure the patient will not move

•Requires patient’s voluntary cooperation

•Most of these devices are used for more than one patient

Positioning Aids/Devices List

•Headrest

•Duncan (prone)

•Timo (solid)(Do not treat through)

•Silverman (Clear)(Treat through)

•Sponge

•Prone Pillow

•Accuform

•Thermoplastic Mold/Mask

•Closed Face (short/long)

•Open Face (short/long)

•Sframe Head Holder

•U-Frame Head Holder

•Wingboard

•Vaclok

•Breast Board (Supine Angle)

•Prone Breast Board

•Belly Board

•Sponges/Wedges

•Biteblock

•Shoulder Pulls

•O-rings

•Table Pad

•Knee Sponge

•Log

•Red Knee Sponge (Index)

•Angled knee sponge

•

Simple Immobilization Devices

Commonly used in addition to positioning aids

•Provide some restriction of movement and stability in cooperative patients

•Still does not prevent the patient from moving

•Can be used with more than one patient

•Cost effective

Has settings, but can use it on all patients

For example, knee sponge

Intermediate Immobilization Devices

Can be used with more than one patient

•The settings can be customized to the patient’s position

•Cost effective

•Commonly used with positioning aids

wing board, prone breast board, supine breast board

Breast Board Supine/Prone

•Adjustable settings on both of these

•Angled Breast Board used to help with larger breast that when lying flat the tissue falls up in the neck area.  Using the angle allows gravity to help pull the breast tissue inferior away from the shoulder/neck area.

•Prone Breast Board used for breast where the tumor might be close or on the chestwall.  This position allows the tissue/tumor bed to pull away from the chestwall decreasing lung dose.

Complex Immobilization Devices

Use most often with each treatment due to the complexity of treatment planning

•Each device is individualized

•More costly because some can not be reused

•Custom=Complex

Masks, bite lock (keeps tongue down while treating), Vaclok

Vaclok

•Vacuum pump and outer rubber bag filled with plastic minispheres

•Vacuum with fine mesh filter takes all the air out causing the minispheres to lock together around the patient position

•Vacuum procedure is complete when the bag is rigid

We reuse but its customizable

Indexing

•Improves setup accuracy and consistency from simulation to treatment across sessions

•Ensures precise patient positioning on the couch during treatment

•Allows dosimetry to enforce stricter tolerance in the record and verify process

•Reduces overrides

More consistent- makes patient be in same place everyday

Having the bar

What is index, what is not?

Index- makes it so the patient gets on the table every time vs if not indexed, the patient can move all over

Indexing

•The tabletop features several indentations labeled H3, H4, and so on

•H=head of table

•F=foot of table

​

This Sframe would be documented as indexed at H3

Allows for increased accuracy in treatment set-up reproducibility from simulation to treatment delivery

Linac

 After the patient has completed the simulation process, a “dry run” is usually done the day before treatment starts.

“Sim and Start”

Sim and 1^st treatment are done on the same day.

Reproducibility

Daily reproducibility is essential

•Patient’s age

•Weight

•General health

•Anatomic area to be simulated

•

All of these things matter in selecting positioning for effective treatment

If the patient is not (somewhat) comfortable and does not remain still during treatment administration,

 then the sophisticated treatment plan and fancy immobilization devices are not effective

Some examples- someone with a broken shoulder cause of metastic cancer. Or older lady really skinny, need to put a pad on table to make more comfortable

Effective Immobilization

•Aids in daily treatment setup and reproducibility

•

•Reminder to the patient to remain still

•

•Should be of minimal discomfort to the patient

•

•Increases precision and accuracy of treatment on daily basis

Patient Positioning

One of the weakest links in treatment planning is …

•Advancements in medical imaging

ADVANCEMENTS – Image fusion is often used on modern planning.

•Radiation oncologists define the target not just in 2 dimensions but also in 3 and 4 dimensions (4th being motion).

IGRT & IMRT allow dose escalation

•Goal of radiation therapy and simulation procedures

In many cases, the ultimate success of treatment is directly related to the effectiveness of the simulation procedure. This procedure determines and documents patient immobilization and positioning for their course of treatment.

Intensity-modulated radiation therapy (IMRT)

treatment technique. can modulate intensity of beam within a tumor volume. Allows us to give more dose to certain areas

Image-guided radiation therapy (IGRT)

before treating patient, you need to image right before beam on

Usually IMRT and IGRT go hand in hand

Localization-

used to identify the tumor (usually done with CT scanner) helps determine what angles to deliver the dose

Contour-

outline structures/ tumor

OARs-

Organs at risk

Verification-

makes sure treating correct tumor

Radiopaque marker-

helps define where we want to expose

Separation-

want to know the thickness being treated: from where the beam will enter to exit: can use calipers, but usually done with CT scanner

Field size

size of treatment area

Interfraction motion-

any motion (especially as changes come as treatment goes on) if patient is in more pain etc

GTV

Gross Tumor Volume

CTV Clinical Tumor volume

cancers can potentially grow outward, so we want to include this area in treatment

PTV

Planning target/tumor volume

Do we still use conventional simulations?

yes

•Conventional simulations

Designed to simulate:

•Mechanical factors

•Geometric factors

•Optical conditions

CONS:

Fluoroscopy-based simulations

Physical measurements

2D imaging

EPID (Electron portal imaging device)

replaced the fluoro tube on the conventional simulator

CT Sim or Virtual Sim

•View of anatomic data in 3 dimensions

•All tissue densities are easily visualized and manipulated

•Much more efficient

Simulation

 should define the anatomic area to be treated so that it is reproducible for daily treatment. An elaborate and complicated simulation is of no value unless it is reproducible on the treatment unit.

Simulation Procedures

•Team approach

•Equipment requirements

oCT scanner with fast acquisition time, multi-slice technology, axial and helical scanning capability, and a wide bore larger than 75 cm, flat couch top

oOther options include gating technology (4DCT) and SGRT technology

•Verification of a treatment field- The localization and verification of a treatment field during CT simulation must reflect precisely what will happen in the treatment room when a prescribed dose of radiation therapy is delivered.

•Immobilization

•Policies and procedures

Benefits of CT Simulation

•Outline critical structures

•Delineate target volume

•Achieve optimal beam placement

•Boost fields planned without patient present (treats just small field within a field)

•Beam’s eye view (BEV)- (looking at the tumor field from the view of the beam)

•Electronic field shaping

•Construction of digital reconstructed radiographs (DRRs) (Digitally reconstructed radiograph)

•Calculation of dose distribution

BEV (beams eye view)-

looking at tumor field from the view of the beam

Boost field-

treats small field within a field

Considerations and Limitations
of CT Simulation

•Bore size (depends on what immobilization device used and position)

•Width and shape of couch

•Laser system (isocenter)

•Acquisition and patient marking time (better than in conventional sim)

•CT numbers in dose inhomogeneity corrections

•Setup parameters and treatment accessories unable to be verified

•Must visualize entire contour (need to make sure nothing is bumping up against scanner)

the more immobilization for safety and accuracy

The higher the dose

•Special Procedure Immobilization

–Stereotactic radiosurgery

–Stereotactic body radiation therapy (SPRT) (anywhere to 5 treatments, with super high dose)

Computed Tomography Scans (1 of 5) POSITIONING

•Patient Positioning

–Lock patient and immobilization device into place on the table.

–Position patient carefully with the treatment area in the center of the CT bore and scan field of view.

–For diagnostic CT imaging, FOV offsets are common.

–Clinically straighten the patient by using the external laser system and any useful topographic anatomy. Temporary reference marks can then be drawn on the patient.

–Know if the immobilization should and can fit through the bore of the CT scanner.

Computed Tomography Scans (2 of 5)

•Topograms (scout)

–The first images acquired during the CT simulation

–It may be an AP scan, lateral scan, or both

–Used to assess alignment of the patient in the CT bore

–Geometric tools in the scanner software aid in patient readjustment

•Data Acquisition

–Select an appropriate scan protocol (usually site specific) with parameters (that may be adjusted)

–Once CT images have been acquired, they are exported via DICOM and imported into simulation software

Topogram

AKA surviews, pilots, scouts, scanogram images

•Methods of Simulation With Computed Tomography Images

–Shift Method

–No-Shift Method

–Techniques for Isocenter Localization

–Integration With Treatment Planning

Shift method-

have to go a certain distance because it is not marked

No-shift method-

line up at original marks. The doctor lines up and marks it

Computed Tomography Scans (5 of 5)

•Patient Marking System

–Isocenter or field edge marking systems are available for CT

–Using temporarily marked reference points, the computer calculates the isocenter with reference to the temporary marks

ØLAP laser company’s CT positional laser system

•Documenting Data

–Organized per institutional standard

–Immobilization devices must be documented

–Also recorded: exact field size, gantry position, shielding, and isocenter

–Completed treatment plan is exported in the record-and-verify system

DOCUMENT IN PICTURES AND WRITING

Use of Four-Dimensional Computed Tomography in Virtual Simulation

•Respiratory Gaiting

–Breathing motion artifacts

–Four-dimensional scanning

–Spirometer

–Maximum intensity projection (MIP)

•Surface Imaging in Radiation

•Magnetic Resonance Imaging in Simulation

•Magnetic Resonance Imaging—Only Simulation

•Positron Emission Tomography-Computed Tomography Imaging

Respiratory Gaiting-

how much does the tumor move while breathing so we know how much to treat

Room Design

•Space Allocations

–The room should accommodate the machine, its components, and its full range of motion.

–Space should be allocated for a good-sized counter with sink, workspace, writing area.

–There should be ample storage for simulation equipment, spare simulator parts, and immobilization devices.

–The control area should be large enough to house several pieces of equipment, a work area, and several personnel.

•Other Considerations

–Appropriate room ventilation per simulator manufacturer

–Correct lighting system that is adjustable

–CT simulator external positioning and patient marking lasers

–Shielding design

Quality Assurance

•AAPM Radiation Therapy Committee Task Group 66

•Daily warm-up and QA

•Monthly QA

•Yearly QA

Electrons block

treat more superficial

Photon blocks

penetrate deeper

STD

Source to tray distance

Electron block

lThickness is much less-not as much block is needed because the energy used is lower

lThere is NO divergence

lSource to Tray Distance (STD) is 95cm.

Photon block

lMuch thicker block is needed because you are using stronger energy

lThere is divergence.

lSource to Tray Distance (STD) is 60-65cm.

Positive or Negative

**The acceptable range (%) of beam transmission through a block is 2-5%

Positive block-

when an actual structure is blocked

so we are treating everything around what is blocked

Negative Block-

block-blocking everything except the area to be treated. Ex Primary brain, electron

Electron field blocking

lCustom cutouts

lStandard cutouts

lLead

Electron Beam Accessories

1.Cones – limited to a few select sizes

2.Electron cutouts – Custom made to collimate and shape the treatment field

3.External shields – Placed to shape and protect critical structures

4.Internal shields – Tissues directly in front of the shield may receive 30% to 70% higher dose. Internal shield must be covered with low atomic # material to reduce backscatter ex. Eye shields, dental wax

5.Tissue Compensator – even out irregular surface placed directly on patient (bolus)

Internal shields-

shields- put lead inside for example for a eye or nose so the radiation doesn’t keep going

Decreases irritation