Treatment Techniques - Exam 3

Beam Shaping Devices: Types

- Machine Collimators - Custom Blocks - Standard Blocks - Mulileaf Collimation (MLC)

Electronic Medical Record: R&V

- Prescribe treatments - Create and edit plans - Track doses - Review reference images - Record/monitor and evaluate patients health through out their course of tx >> Weight >> Vital signs >> Labs - Perform chart audits - Scheduling - Charging

"Beam Off" (Interruption)

1. Press "beam off" key 2. Turn key to off position 3. Open treatment room door

Treatment Delivery Procedure

1. Review patient chart 2. Prepare room 3. Check patient ID, verify correct site, markings and procedure to be done 4. Explain procedure 5. Assist patient onto tx. table, locate patient markings 6. Raise couch and set appropriate SSD 7. Align patient with lasers 8. Set gantry and collimator angles 9. Position blocks and confirm with field light 10. Position other beam modifying devices 11. Inform patient you are leaving the room; reassure them of audio and visuals 12. Monitor patient 13. Set machine parameters and verify with R&V system 14. Initiate "beam on" and monitor patient 15. Multiple fields: re-validate all parameters 16. Assist patient off table at completion of treatment 17. Complete patient's treatment chart 18. Prepare room for next patient

Block Cutting Process

1. film place on block cutting system light table 2. appropriate TFD (SFD) is set 3. styrofoam block is placed in cutting system 4. pointer from cutting system is used to trace the outline of the field 5. at same time is cutting the shaped into the styrofoam block 6. styrofoam mold is sprayed with water to prevent cerrobend from sticking

Electron Block Cutting Process

1. obtain outline from DRR or from template 2. template is used to form a mold 3. mold is made from cut styrofoam 4. styrofoam mold placed on top of lucite cut out & held into place while cerrobend is poured 5. after cerroben hardens, cutout is knocked away from styrofoam

POP

180 degree Hinge angle Enter patient from 2 directions - AP/PA - Laterals - Obliques

Double Exposed Sim & Tx Fields (Procedure)

1st Part - set correct field size - put blocks in, or engage MLC's - expose film (this will be the actual treatment area) - take blocks out 2nd Part - open field size - make another exposure with the field size opened - NO BLOCK IN

Stereoscopic Imaging

2 images from different angles focused on the same point - Orthogonal films are an example (Defines isocenter)

Verification Imaging

2 types of radiographic film: - Port film > Film that is placed in a cassette > React more slowly to radiation exposure than diagnostic film allowing images to be created using the linear accelerator energies - Verification film (V-film) > Even slower film that allows film to be left in place during entire treatment Cassettes are positioned in a slot under the treatment couch or cassette holder.

IGRT - EPID

2 types: - Scintillation screen and television camera - Amorphous silicon flat panel detector > Consists of an array of photodiodes that detect light from an x-ray-simulated scintillator System is lightweight - Retractable arm along the gantry's axis - Arm has an image intensifier to improve the image - Better quality than regular port films

IGRT (CBCT)

A linear accelerator with a kilovoltage source on the left and a flat-panel detector on the right. The gantry rotates 360 degrees around the patient while a series of radiographs are taken. These radiographs are constructed into a three-dimensional computed tomography data set.

Lead (Advantages/Disadvantages)

Advantages: - dense - absorbs radiation Disadvantages: - high MP - high BP - toxic & carcinogen

Emergency Procedures

All departments will have an emergency plan to follow in case of machine malfunction or fire. If abnormalities are observed in the radiation output (from outside the room): - Depress the "Beam Off" button on the console and turn disable / enable key to disable position - If that fails, depress "Emergency Off" button on the console - If that fails, place the "Main Circuit Breaker" to the "Off" position - Remove patient from the room (if emergency off button was used, emergency back up pendant will have to be used to lower the treatment table) - Record the monitor units displayed on the front of the console electronics cabinet

Cerrobend

Alloy - bismuth 50% - tin 13.3% - lead 26.7% - cadmium 10% (toxic & carcinogen) Acronym --> "BLT without a Coke" 83% of density of Lead 70 celsius MP

IMRT (Intensity-Modulated Radiation Therapy)

An advanced form of 3-D conformal treatment by using "inverse treatment planning" - oncologist selects the dose parameters to normal tissue and the target volume and the planning computer determines the optimal treatment parameters. Delivers nonuniform exposure across the BEV by using a variety of techniques and equipment Radiation intensity is varied or modulated across the exposed field, allows critical structures dose to be reduced 2 Types: Segmental & Dynamic

Monitoring Patient during Treatment

Audio - 2 way communication Visual - 2 cameras, close up and long view Inform patient of monitoring prior to initiating treatment

Electron Therapy Shielding

Common electron tx sites: - Nares, auricle, eyelids, and lips - Thin structures that require shielding for underlying normal tissues (lens, lacrimal duct, nasal membranes, gingiva etc.) - Place shields between tumor and normal structures Metal shields are covered with a low Z number, it will reduce the low-energy scatter from the shield - Aluminum, tin or paraffin wax

Verify actual treatment being delivered

Compares machine settings with those prescribed and prevents beam on if settings are out of tolerance - Tolerance usually set by physicist Defines and records the patients complete course of therapy.

Compensating Filters

Compensate for a sloped surface Units deliver a dose of radiation across a plane perpendicular to the radiation beam. The dose distribution can be evened out by compensating for the irregular surface. We can use bolus to fill in these areas of irregularities but we loose the skin sparing effect of the higher energy linear accelerators. Compensating filters can be positioned in the head of the treatment unit, which will modify the radiation beam to accommodate the contour of the patient. The compensator should be placed as least 20 cm or more away from the skin surface to preserve skin sparing properties of the megavoltage beam Compensators can be made from a variety of materials as long as the materials equivalence to tissue absorption is known. • Common materials include: • Copper • Aluminum • Brass • Lead • Lucite

Record & Verify Systems

Computers that assist the therapist in verification of parameters - Verify actual treatment being delivered - Computer assisted set up - Records patient data - Allows for data transfer from sim and treatment planning - Assist in quality assurance

Room Prep: Before Patient Arrival

Confirm treatment setup, F.S., gantry, collimator and table positions - Set F.S. - Make sure lasers are visible - Make sure table is positioned the correct way - Big window, tennis racket Make sure treatment table and accessories are cleaned after each patient and new linens used

Wedges

Cut at different angles Made of: - aluminum - lead - plastic Labeled with machine used for, angle, max FS Always computer coded for machine Used for: - compensation for lack of tissue - eliminate hot & cold spots - create a more homogenous dose distribution designed to change angle of isodose curve relative to beam at specified depth Reduce the dose to areas of overlap between fields that have a hinge angle less than 180 degrees Wedges have field size limitations and care should be taken to make sure there is no flash over the heel or the sides of the wedge

Emergency Procedures: In case of FIRE

Depress "Emergency Off" button on console Remove patient to safety (use emergency pendant) and notify personnel in adjacent rooms Activate nearest fire alarm box Determine if evacuation of entire floor is required Use fire extinguisher to try and extinguish fire

Emergency Procedures: In case of Mechanical Failure

Depress "Emergency Off" button on the console Enter treatment room and remove patient to safety (use emergency pendant)

Transmission Filters

Designed to allow the transmission of a predetermined percentage of the treatment beam to a portion of a treatment field and may be used throughout the course of treatment. These blocks are made allowing more than the 5% transmission and act as a filter to some of the radiation. This allows the physician to treat different anatomical structures with different doses in a single treatment field.

Beam Modifiers (+ Types)

Devices that change the shape of the treatment field or distribution of the radiation depth Modify radiation dose across the treatment field Types: Bolus Wedges Virtual Wedges Compensating Filters Transmission Filters

Electron Treatments

Electron beams provide a rapid dose build up, an area of uniform dose deposition, followed by a rapid dose fall-off The gantry is angled to bring the beam surface as close to parallel with the treatment surface as possible and collimation is brought closer to the treatment surface - Special consideration is given to beam collimation, shielding and bolus requirements Due to electron scattering, collimation close to the treatment surface is needed to improve dose distribution by sharpening the dose gradient at the beams edges It is important to know the depth at which electrons deliver a dose to the 80% or 90% isodose line is approximately 1/3 (80%) to ¼ (90%) of it's energy - (12MeV/3= 4 cm depth) The most useful treatment depth or therapeutic range of electrons is given by the depth of the 90% depth dose Shielding for electron blocks is less than that of photons, only several cm's are needed as compared to 6 cm or more for photons Electron cutouts, electron shields, field-defining cutouts - collimation that also shape the electron treatment field - The electron cutout fits into the base of the cone

Verification Imaging (Types)

Electronic portal imaging devices (EPID) - OBI Port films using cassettes In room CT scanner KV cone-beam MV cone-beam Ultrasound

Treating with Electrons / Cones

Electrons used to treat superficial areas - provide rapid dose build up close to skin surface followed by rapid fall-off Collimation needed to decrease scatter from electrons - cone added to increase collimation to treatment surface - electron cutouts are made from template - some standard cutouts

Verification Imaging (Frequency of Films)

Films are taken on the first day of treatment and every 5th treatment to verify the actual treatment portal If marks are unstable, films are taken daily for placement of isocenter If patient loses marks, film must be taken Some patients are imaged daily to check for placement of fiducials and other reference marks within the patient allowing placement of the isocenter

Verification Imaging (Disadvantages)

Films taken with linear accelerators, MV, usually have poor contrast, making landmarks hard to see Films are checked after treatments are given so no chance to correct that treatment If films are taken and checked before treatment, have the worry about patient movement while processing the film

Wedge-Pair technique

Hinge angle between 2 ports is decreased Dose in area of decreased hinge angle is decreased Overlapping isodose lines are not parallel to each other - added to improve dose distribution - dose is reduced in shallow regions so dose is more homogenous throughout the target

Treatment Plan

IMRT protocol, 12 fields

Machine Collimators

Jaws - define x/y dimensions of the beam - limits beam shape to rectangles

Malfunctions or discrepancies in treatment must be recorded and reported

KNOW

Ellis Comp Filter

Made of brass & aluminum blocks Measurements have to be taken of the patient in order to properly construct the ellis comp filter A rod box is used to get the required measurements - positioned within the accessory mount and rods pushed to surface of the patient resulting in a contour of the patient's anatomy

Backup System

Monitor Units Time

Arc Therapy

Multiple field technique Radiation is delivered as the gantry moves through its arc of rotation

IGRT (Brain Lab ExacTrac)

Not attached to the linear accelerator Uses two floor-recessed x-ray units and 2 ceiling-mounted amorphous silicon flat panel detectors Images are analyzed and couch corrections calculated

Initiation of Treatment Dose

Once treatment parameters are confirmed the therapist can "beam on" - Initiation of "beam on" requires a key, pressing a button or both - Console will display >> Dose rate >> Time - Monitor units - Lights will flash outside and inside the room indicating beam on

Patient Transfers

Patient may need assistance onto the table - Wheelchair - Stretcher - Supportive arms to get on table Be aware of O2, tubes and catheters when putting patients on table Use proper body mechanics when assisting patients onto the table

Total Body Irradiation (TBI)

Patients positioned at a great distance to achieve a large field size Patient usually placed in fetal position on stretcher against wall in treatment room Patient is treated with arms down to lower the dose to lungs Patient wraps their arms around their ankles to help hold feet in the field Gantry is angled 90 degrees Patient are treated POP, with repositioning the patient to treat the other side halfway through the treatment Lead shield is placed on treatment tray to block critical structures in the head

Positioning Port Films

Perpendicular to the beam Maximize the SFD Radiopaque markers indicate the position of the port and central ray Graticule is used

"Beam Off" (Termination)

Press an emergency off button located on (this will shut the machine down): - Treatment console - Inside the room, on the treatment couch, gantry stand and room wall >> The emergency button needs to be depressed after pressing for emergency and there will be a time delay for restarting the machine Emergency pendant (located in gantry stand) may be needed to lower patient in the event the machine has been "shut down"

Treatment Console

Provides information regarding treatment - Monitor units - Time - Dose rate - Energy - Interlocks

After Room Prep

Radiation Therapist greets patient Properly identify the patient Verify correct site, markings and procedure to be done Have good, open communication with patient - Explain step by step what you will be doing - Explain care of skin marks, skin care and nutrition Evaluate condition of the patient, daily - Should the patient be treated?

Image-Guided Radiation Therapy (IGRT) - Newest Technology -

Rationale is to image the patient just before treatment and compare the position of external setup marks and internal anatomy to the treatment plan - Shifts in patient position are made before each treatment delivery, if needed Variations that can cause shifts prior to treatment include - Respiratory motion - Movement of body parts - Weight loss - Radiation induced changes (shrinking of the tumor) Used in a variety of forms: - EPID (called interfraction) - In room CT scanner (called intrafraction) >> KV cone-beam CT >> MV cone-beam CT - Ultrasound IGRT tracks changes in pt. positioning due to variations

EPID (+ Advantages/Disadvantages)

Replaced films in the clinic Obtains images in a digital format - Images can be reviewed from multiple locations Advantages - Radiation therapist and physician can verify the isocenter position and location of treatment field prior to treating and is done quickly and accurately - Images can be viewed immediately online at the treatment machine or later with offline tools Disadvantages - High imaging dose - 1 to 5 cGy - Low quality of image due to high energy > Poor image quality (poor contrast) > bony anatomy hard to see

Room Prep: Basic Info

Room engineered around an isocenter Lasers projected from 3 to 4 points Standard and dim lighting is required in room

Verification Imaging

Setup and portal verification imaging necessary - Taken on the treatment unit with the patient in the treatment position - The films are reviewed by the physician who will accept them or make an adjustment Documents the actual treatment given by providing a visual confirmation of the planned treatment Identifying anatomy is vital for comparing on-board images with the DRR or other images used as "masters"

Dynamic MLC IMRT

Sliding Window Technique Moves leaves through one beam on/off sequence Field-in-field technique may be facilitated using MLC's to deliver additional dose to a subset of a larger treatment field - this is a forward planning technique used to achieve a more desirable dose distribution

Custom Blocks (+ Advantages/Disadvantages)

Specific blocks made for each individual patient - made of lead or cerrobend Advantages: - divergent - more accurate - setup faster (blocks lighter) Disadvantages - not readily available - if block is changed or moved, have to make a new one - expensive

Segmental MLC (SMLC)

Step & Shoot Emits beam called beamlet. A small photon intensity element used to subdivide an IMRT beam for calculation purposes Process: - 1st beam is delivered - the beam turns off - the leaves are moved to a new position - again the beam is delivered - the beam turns off and on until all fields are treated

IGRT (kV imaging)

System is installed on the linear accelerator at right angles to the treatment beam > Provides radiographic or cone-beam CT modes for imaging Images resemble conventional simulation images and diagnostic images More info about soft tissue and bony anatomy Uses a source of KV x-rays Flat panel image detector On board imaging of internal fiducial markers help track set up inaccuracies before or after patient treatment With or without fiducials, daily checks of patient positioning can be done before and/or during treatment

Hinge Angles

The measure of the angle between central rays of 2 intersecting treatment beams When a second beam is positioned directly opposite another beam, the combined dose distribution is relatively even throughout the volume. As the hinge angle decreases, dose delivered to overlapping areas will vary significantly creating areas of high and low dose regions in the desired target volume. To reduce the dose in areas of overlap a wedge can be used during treatment. Changing the beam angle can change the area of the hot and cold spots by changing the angle of the two intersecting beams.

Monitor Units (+ factors)

The time the treatment machine is on in order to deliver a prescribed dose Factors effecting the number of monitor units per patient and tx port - Beam energy - Distance from the source of radiation - Field size A calculation is done to determine the amount of MU

Virtual Wedges

The use of a moving collimator jaw to produce a wedged field A moving jaw system is applied, the jaws starts at one end of the field and opens to a full field over delivery of the dose. The side where the jaw movement begins is considered the toe of the wedge (receives more exposure)

Make-Up of Wedges

Thick end called the HEEL - Attenuates the greatest amount of radiation, draws the isodose lines closer to the skin surface Thin end called the TOE - Attenuates the least amount of radiation will give this part of the treatment port more dose than that at the opposite end When using wedges, the heels are typically positioned together - The wedged pair technique changes the volume receiving radiation by decreasing the hinge angle between 2 treatment fields

Useful Landmarks for Image Comparisons (Thorax, C-Spine, Abdomen)

Thorax - Carina located at the level of T4-5 C-spine - C4 - Level with the thyroid cartilage and beginning of the larynx Abdomen - Iliac crest located at the level of L4, greater trochanter can be used to horizontally align the patient

Bolus (+ Made of, Application)

Tissue equivalent material that conforms to treatment surface without air gaps Made of: - wet towel - super flab - water bags - paraffin wax - wet gauze - vaseline gauze Bolus thickness equal to the Dmax dose of the energy being used will eliminate skin sparing effect of the MV beams Will improve dose distribution Application: - entire treatment area - over scars - superficial nodes - areas of concern

4 Field (Box Technique)

Treat deep seated tumors - pelvis - abdomen Fields arranged 90 degrees from each other - AP/PA/RT/LT Lateral Usually requires backs for shaping fields

Electronic Portal Imaging Device (EPID)

Used for imaging on linear accelerators Method of improving treatment field accuracy and verification Used to check internal structures during the entire treatment process, prior to treatment with the aid of computer software Use the machines MV energy, quality not always that good. Used to detect: - Patient movement during treatment - Organ movement - Patient positioning for breast and abdomen setups

Photon Blocks

Used to shape a photon or electron field Mound on clear lucite tray attached with screws - inserted into accessory holder Thickness of block depends on energy being used - should not exceed 5% no matter the E being used

Superficial

Used to treat skin cancers or tumors no deeper than .5cm, due to the rapid falloff of the radiation Application of superficial treatments include the use of a cone or applicator - Cone sizes are usually 2 to 5 cm in diameter - Lead cutouts are made to fit the treatment area. - The cone lies directly on the lead cutout usually at a distance of 15 to 20 cm

Tangentials

Used to treat superficial volumes - Breast - Ribs

Double Exposure

Used to visualize the treatment area as well as surrounding anatomy, increasing the number of landmarks available for interpretation of the film and port placement

Single Exposure

Used when sufficient anatomy for verification are located within the treatment area

Half Value Layer/Thickness (HVL/HVT)

amount of material required to reduce intensity of the beam by 50% can't have more than 5% transmission through a block

Orthogonal Films

an example of Stereoscopic Imaging 2 films taken at 90 degrees of each other; used for patient with multiple beam arrangements to verify the isocenter of the treatment field

Conformal Therapy (IMRT)

applies 3D localization of tumor volume - 6 or more fields - couch & gantry rotations

Stereotactic Body Radiation Therapy (SBRT)

designed to deliver a high-dose of radiation to the target utilizing either a single dose or small number of fractions (as many as 5)

Multileaf Collimators (MLC's) (+ Advantages/Disadvantages)

leaves of lead that close on a field (52-160 leaves) - made of tungsten - each position independently allowing variety of shapes - computer controlled Advantages: - provides more flexibility than blocks - increases safety Disadvantages: - can break easily - not as accurate for shaping irregular fields

Block Cutting Systems (+ disadvantages)

mimic geometrical arrangement of the beam allowing proper divergence & magnification at the treatment site Disadvantages: - space requirements - lifting heavy equipment - exposure to hazardous chemicals - use of power tools - adequate ventilation in room

Lucite Filter

only compensates in one dimension and is done with sheets of plastic compensates for the slope on the surface of the patient When constructing the lucite comp filter, a sagittal contour is taken of the patient. Once the compensator is made it is placed in the accessory mount of the linear accelerator during a patient's treatment.

Stereotactic (SRT stereotactic radiation therapy)

use of high-energy photon beam with multiple ports of entry convergent on the target volume

Image Guided Radiation Therapy (IGRT)

used to image the patient right before treatment Compares external marks and internal anatomy against the treatment plan Shifts or adjustments can be made before treatment (as opposed to the regular port film) DRR's are downloaded from the treatment planning system and used as a comparison with the images obtained on the linear accelerator When comparing, bony anatomy or soft tissues are superimposed to calculate shifts when aligning the patients IGRT can track changes in patient positioning as a result of the following variations: o Respiratory motion o Body movement o Internal structure movement o Weight loss o Radiation-induced changes (tumor shrinkage)

Interlocks

• Closing doors • Placement of proper beam modifiers • Machine operation requirements • MU (with R&V) • Energy (with R&V) • Pendant

Settings with Tolerances

• Gantry • Collimator • Table angle • Monitor units or time • Aperture settings • Beam modifiers • Arc versus fixed treatment