Endterm Flashcards by Lee Vincent Neolar

A type of external beam radiation therapy (EBRT), stereo means 3-dimentional and tactic means probe, allows radiation beam to be given to a very specific are usually the brain, best for very small tumors, it can be completed in one-five days rather than over several weeks

Stereotatic radiotherapy

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Delivers a single high dose of radiation to the tumor (called single fraction), this treatment doesn’t envolve surgery. An incision (cut) is not made and tissue is not surgically remove. __ is delivered by a team involving radiation oncologist and neurosurgeon.

Used to treat conditions involving the brain or spine including: CA that starts in the brain (gliomas, and other primary brain tumor, brain metastases, benign tumors arising from membranes covering the brain (meningiomas), abnormal blood vessels in the brain (arteriovenous malformations)

Stereotatic radiosurgery (SRS)

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Gives smaller dose of radiation over a number of treatment sessions (called multiple fraction), until the desired total dose given, it also refers to one or several stereotatic radiation treatment in the body excluding brain or spine.

Small lung CA, lung metastases, liver metastases

Stereotatic radiotherapy (SRT)

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When __ is used the head frame is attached to the skull. A neurosurgeon injects a local anesthesia just under the scalp to numb the area. Then the neurosurgeon places special screws or pins into the skull. These screws or pins fix the head frame to the skull. The skull screws and head frame are removed after the treatment is finished

Stereotatic radiosurgery (SRS)

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When __ is used, a removable head frame or a special mask keeps the head in position

Stereotatic radiotherapy (SRT)

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3 delivery systems

Gamma knife, linear accelerator, cyberknife

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A type of conformal radiotheraphy. Conformal radiotherapy shapes the radiation beams to closely fit the area of the CA. It is an advanced mode of high-precision radiotherapy. Uses a computer controlled LINAC to deliver precise radiation dose to malignant tumor. Allows radiation dose to coform more precisely to 3-dimensional shape of tumor. Allows higher radiation doses to be focused on the regions within the tumor while minimizing the dose to surrounding normal critical structures

Intensity modulated radiotherapy (IMRT)

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Currently, __ is being used most extensively to treat CA of the prostate, head and neck and CNS. Since __ uses a standard radiotherapy machine such as LINAC, it is excellent to use multi-leaf collimator

Intensity modulated radiotherapy (IMRT)

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Persons involved in the procedure in IMRT

Radiation oncologist, medical physicist, dosimetrist, radiation therapist, radiation therapy nurse

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What the px feels during and after the procedure

No pain during the actual treatment with IMRT
machine can be stopped if you experience discomfort due to treatment position or positioning devices
As treatment progress some px may experience treatment-related side effects

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IMRT treatment sessions usually takes between?

10-30 mins

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Early side effects
Depending on the area being treated, other early side effects may include

Hair loss in the treatment area
Mouth problems and difficulty in swallowing
Eating and digestion problems
Diarrhea
Nausea and vomiting
Soreness and swelling in the treatment area
Urinary and bladder changes

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Late side effects
Which are rare, occurs months or years following treatment and are often permanent. They include

Infertility
Brain changes
Spinal cord changes
Lymphedema

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Brachytherapy comes in to 2 treatment procedures:

High dose rate (HDR) brachytherapy and low dose rate (LDR) brachytherapy

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A type of internal radiation therapy, delivers high dose of radiation from implants placed closed to or inside the tumor.

High dose rate brachytherapy

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3 types of HDR brachytherapy

Intracavitary implant
Intraluminal implant
Interstitial implant

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An applicator is inserted into a body cavity to reach the tumor. These are performed in clinic or out patient basis. Local anesthesia and/or conscious sedation is required

Intracavitary implant

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The catheters are inserted into a tube structure such as bronchus, esophagus, or bile duct. These are treated the same as intracavitary implants

Intraluminal implants

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Implants are done in operating room with the px under local, general or spinal anesthesia, interstitial catheters are inserted through the body tissue to encompass tumor. In case of prostate and gynecological cases, a rubber template is sutured to the outside skin to hold the treatment catheters in position, in breast and head and neck cases, the treatment catheters are held in position on the skin by plastic buttons where the catheters enter and exit the skin, it is by means of needles or catheters

Interstitial implant

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Type of internal radiation therapy that delivers low doses of radiation from implants placed closed to or inside the tumor in the body, implants are the same as in the HDR. Sources used are: Ra-226, Cs-137, Ir-192, I-125 and Pa-103. Source handling and loading into the applicator or tissue can be performed manually or remotely by the afterloader with source loading performed by a computerized unit

Low dose rate brachytherapy (LDR)

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In __, tiny radioactive particles the size of rice are implanted directly into the size of the tumor these particles are known as seeds

LDR brachytherapy

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Measurement of the absorbed dose delivered by ionizing radiation calculation and assessment of radiation dose received by the human body used extensively for radiation protection and is routinely applied to occupational radiation workers

Dosimetry

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dose absorbed unit in time. indicates the amount of radioactive dose received by the person within a certain period of time. Expressed in rems or sievert (Sv) per hour.

Dose rate

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Ordinarily measured on the central axis at a standard source surface distance (SSD) at the depth of Dmax in phantom

Dose rate in tissue

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Displays relative doses across the treatment plan consisting of multiple beams

Dose profile

4 radiation quantities and qualities Quantity, (old), name (new), other units

Activity (A), curie(Ci), becquerel (Bq), Ci= 3.7x10^1, Bq 1Bq= dis/s Absorbed dose (D), rad, gray(Gy) Gy= 100 rad j/kg, ms2/s2, 1 Gy= 1j/kg Equivalent dose (H), rem, sievert (Sv) Sv=100 rem Exposure (E), roentgen, coulomb/kg, R=2.58x10-4 c/kg

Used for all kinds of radiation for any material. Energy transferred by ionizing radiation to the interacting medium per unit mass. Unit dose that refers to dose received by the patients

Absorbed dose (D)

D= E= M=

Absorbed dose Energy Mass

Amount of radiation exposure received by the radiation workers, Unit used that refers to the dose received by the radiation workers Formula H=DQN

Equivalent dose (H)

H= D= Q= N=

Equivalent dose Absorbed dose Quality factor 20 for alpha radiation 10 for both proton and neutron 1 for both x-ray and gamma ray Modifiying factor always equal to 1 (no unit)

Device that measure dose distribution within such phantoms The constancy of the machine must have been routinely checked otherwise irreversible harm may be caused either by overdosing – which lead to tissue damage or underdosing – which result in failure to cure. It is advisable to measure the dose actually delivered to the patient by means of __ placed in body cavities or in catheters or needles inserted in the tissues.

dosimeters

at a point is an absorber such as tissue in the energy deposited in small fixed weight of material

Dose or absorbed dose

When radiation beam reaches the patient, the dose delivered to a point within the patient depends on the following.

Dose measurements

depth of calculation point below the surface

a. Depth

penetration power of the beam

b. Energy

type of tissue (muscle, bone, fat) that the beam must penetrate

Density

distance from the radiation source to the skin surface

SSD

size of the field on the skin surface An essential step in treatment planning is to establish measured data tables for each treatment machine that will be used.

Field size

tissue equivalent material or dummy patients The __ material used is often water, which is like soft tissue as far as radiation absorption is concerned.

Phantoms

3 devices most commonly used for dose determination

1. Ionization chamber 2. Thermoluminiscent dosimeters (TLD’s) 3. Photographic film

a comparison between measurements comparison between the standard unit and the unit under test

Calibration

calibrates the safety machine and checks all the safety system so that the characteristics of the machine and dose delivered are known to a highly degree accuracy

Medical Physicist

allows certain judgements to be made relative to the adequacy of the therapy

Accurate calibration

constructed to shield critical organs in the treatment portal commonly used for the treatment of thyroid, kidneys, liver, lens of the eyes and lungs. the blocks are placed in a tray attached to the head near the collimator of the machine

Special blocks

often slopes away from the normal cross-sectional areas of the beam. This creates an air gap.

Skin surfaces

devices to compensate for the air-gap

Bolus and compensating filter

made up from tissue equivalent materials whose properties simulate those of soft-tissue and may be filled with rice or water.

Bolus bag

perform essentially the same functions as bolus bags but are individually designed by the physicist according to the patient contours. §Tissue compensating filter generally preserve the skin-sparing properties of the radiation.

Tissue compensating filter

Probably have the most contact with the patient. Must have a cheerful and sympathetic attitude. Assist the oncologist and the physicist during the first treatment in placing the patient in treatment position. The position of the patient and the size of the treatment will be checked by dimming the lights in the room and making use of field lights located in the head of machine.

Radiologic technologist

lights on the sides of the room which are used to check the height of the treatment table

Sidelights

illuminates an area that coincides with the radiation treatment field on the patient’s skin

Field lights

3 MOST IMPORTANT TISSUE ABSORPTION FACTORS

a. TMR b. TAR c. PDD

Include both primary dose and the dose due to scatter in the irradiation volume.Dependence on the field size increase with a increased FS(field size) Varies inversely with the square of the distance from the source

Dose rates in phantom

TISSUE ABSORPTION FACTORS a. PDD - b. TAR – c. BSF – d. TPR – e. TMR –

percentage depth dose Tissue Air Ratio Back scatter Factor; TAR in Dmax Tissue Phantom Ratio Tissue Maximum Ration

depth dose ratio express in percent absorb dose at a given depth expressed as a percentage of the absorb at reference depth on the central axis of the field. the reference depth on the central axis of the field. affected by energy, field size, SSD and by composition of the irradiated medium PDD also change with depth. dmax – reference depth.

PDD (PERCENTAGE DEPTH DOSE)

as the FS is increased, the absorb dose in a medium is greater due to the increased scatter, thus the PDD is increased.

Dependence on FS and Shape

Higher energy beams have greater penetrating power and thus the PDD at a given depth and SSD is increased

Dependence on energy and depth

absolute dose rate decreases with increased distance from source PDD increase with increased distance

Dependence on distance

ratio of the absorb dose at a given depth in phantom to the absorb at the same point in free space or in air TAR is independent of SSD Is the ratio of the dose at a given point in a medium to the dose at the same point in free space For given energy, the TAR depends on depth and FS but independent of the distance.

Tissue air ratio (TAR)

first introduced by Karzmark in an effort to overcome the limitations of the TAR the ratio of dose at a specified point in tissue or in a phantom to the dose at the same distance in the beam at reference depth, usually 5cm. sometimes used instead of TAR in dosimetry of high energy beams Retains the properties of TAR but eliminates the difficult and unreliable measurements in air.

TISSUE PHANTOM RATIO (TPR)

a special case of TPR where the reference depth is chosen to be at Dmax.

TISSUE MAXIMUM RATIO

ratio of dose rate with a scattering medium (water or phantom) to the dose at the same point without a scattering medium (air) at the level of maximum equilibrium. TAR at the level of Dmax independent of SSD but depends on the energy and the FS

BACK SCATTER FACTOR (BSF)

is the gross palpable visible and/or tissue demonstrable extent and location of malignant growth The volume of known disease

GROSS TUMOR VOLUME (GTV)

is a tissue volume containing the GTV and or subclinical microscopic malignant disease The volume that must always be enclosed by the treatment isodose Untreated portions of the CTV could lead to a local failure of therapy.

CLINICAL TARGET VOLUME (CTV)

also known as standard ionization chamber. instrument used in the measurement of roentgen used for the calibration of secondary instruments designed for the field use. Too delicate and bulky for the routine use.

FREE AIR IONIZATION CHAMBER

Shaped liked a sewing thimble Has a wall-thickness of 1mm or less with closed fitting caps made up of Plexigals §Most commonly used wall materials are graphite, bakelite or a combination of both

Thimble Chambers

Provide a stable and reliable secondary standard for x and gamma rays for all energies in the therapeutic range

Farmer Chamber

Basic method of determining absorbed dose in a medium Used a thermistor to measure in small rise temperature. Thermistors are semi-conductors that shows a large change in electrical resistance with a small change in electrical resistance with a small change temperature about 5% or 1 degree Celcius.

Calorimetry

The energy absorbed from ionizing radiation may produced a chemical change and this can be determined to measure the absorbed dose

Chemical dosimetry

also known as the Fricke Dosimeter Consist of ferrous sulfate or ferrous ammonium sulfate and sulfuric acid

Ferrous sulfate

Radiation chemical yield may be expressed in terms of the number of molecules produced per 100 eV of energy absorbed.

G value

Lithium fluoride is the most extensively studied and most frequently used for clinical dosimetry Has an effective atomic number of 8.2

Thermoluminescene Dosimetry

a geometric volume the dimension believed to always contain the CTV. Includes margin around CTV It allows for target motion and uncertainty in positioning.

Planning target volume

Two types of technique

Sad technique Ssd technique

involves the measurement of radiation based on the change in the thermal energy per unit mass of the medium. It is based on the fact that almost all the energy deposited in the medium by the radiation beam eventually appears as heat within the medium. For water, 1 Gy produces a temperature rise of 2.4x 10-4 Calories/gram which can be measured using a sensitive device called thermistors.

CALORIMETRY

based on chemical changes caused by radiation. The chemical radiation dosimeter most commonly used is Ferrous Sulfate in which it is oxidized by radiation into ferric sulfate. Ferric Ion concentration is measured by absorption spectrometry at 224 nm and 304

FRICKED DOSIMETRY

When x-ray film is exposed to ionizing radiation. the exposed siver bromide crystaIs form a latent image. The degree of blackening of the film is proportional to the energy absorbed and is measured by determining the optical density with a densitometer.

FILM DOSIMETRY

measurement of radiation energy based on ion pairs produced in a given mass of medium.

IONIZATION METHOD

- used for photon beam - used for photon - used for electron beam

Thimble Chamber Farmer Chamber beam Markus Chamber

when a crystal is irradiated, a very minute fraction of the absorbed energy is stored in the crystal lattice. Some of this energy can be recovered later as visible light if the material is heated. This phenomenon of the released of visible photon by thermal means is known as Thermoluminescence

THERMOLUMINESCENCE DOSIMETRY

Treatment through one single field arrangement is the simplest treatment and the dose distribution in tissue is essentially as represented on an isodose chart for the particular energy and the field used. With this field arrangement, Electron is usually the type of radiation used to treat shallow tumors where a rapid drop in dose beyond the 57 depth of the tumor.

Single field

-Is a pair of fields directed along the same axis from opposite sides of the treatment volume. are relatively easy to set-up and to reproduced from day to day.cThe 100% isodose line is with in the entire treatment volume. Advantages- Simplicity and reproducibility of set-up Homogenous dose to the tumor Less chances of geometrical miss Disadvantage- Excessive dose to normal tissues critical organs above and below tumors

Parallel opposed fields

The use of multi-fields directed at the target volume requires that the beam entrance and exit of each field be aimed at different angles/segments, thereby reducing the dose to adjacent tissues. The most popular multi-field arrangement is the "box Technique", which is often used in the treatment of pelvic malignancies. The technique consists of opposed anterior and posterior fields and opposed right lateral and left lateral field.

Mult-field arrangement

Endterm Flashcards

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