FINAL II RADTHERA

Shanks Redhaired · 7問 · 1年前

通報

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Absorbed dose measurement methods

Calorimetry Fricke dosimetry Film dosimetry Ionization method Thermoluminescence dosimetry

is the best technique for absolute and direct measurement of absorbed dose.

calorimetry

It is based on the measurement of the temperature rise of a given volume element of this instrument when it is exposed to a source of radiation.

calorimetry

also called ferrous sulfate dosimetry, is one of the most useful chemical dosimeters in existence. This dosimetry technique depends on the oxidation of ferrous ions (Fe2+) to ferric ions (Fe3+) by ionizing radiation

fricke dosimetry

Fricke dosimetry also called as

ferrous sulfate dosimetry

as been applied to measure relative dose distributions in an anthropomorphic polystyrene breast phantom having cork lungs, simulating a radiation therapy treatment with 6 MV opposing tangential beams. ... These results demonstrate that film dosimetry is a useful tool for treatment planning verification.

film dosimetry

provides a real advantage to radiation therapy departments in that it allows rapid and easy calibration of output at the end of treatment cones.

thermoluminescence dosimetry

Dosimetry Parameters

output factor isodose tpr tar tmr pdd sar smr backscatter factor collimator scatter factor

Define as the ratio of the dose rate at the depth maximum dose for the reference field size to the reference field size.

output factor

It represents points of equal dose.

isodose

It is define as the ratio of the dose at a specific point in tissue or in a phantom to the dose at the same distance in the beam at a reference depth, usually 5 cm.

tpr

It is define as the ratio of the dose at a specific point in tissue or in a phantom to the dose at the same distance in the beam at a reference depth, usually HOW MUCH

5 cm

It is the ratio of the dose at a given point in a medium to the dose at the same point in the free space

tar

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

tissue maximum ratio

It is the absorbed dose at a given depth expressed as a percentage of the absorbed dose at reference depth on the central axis of the field.

pdd

It is the ratio of the scattered dose at a given point in a medium to the dose in air at the same point.

scatter air ratio

It is really just a variation of SAR and, like SAR, is mainly used in calculation of scattered dose in phantom or tissue.

scatter maximum ratio

Is defined as the ratio of dose on the central axis at Dmax to the dose at the same point in air.

backscatter factor

Output measured without a scattering phantom, sometimes referred to as in-air, increases with increase in field size.

collimator scatter factor

Typical Field Arrangement

Single Field Parallel opposed field Multiple field Wedge field Moving Beam Treatment

Superficial targets

single field

Important factors to consider in choosing single field

The range of dose within the tumor The maximum dose in tissues The exit dose

Probably the most commonly used field of arrangement.

parallel opposed

Often used to treat metastatic disease in various sites.

parallel opposed

Frequently employed in treating large fields.

parallel opposed

Also often used during a portion of disease of the brain, pelvis, head and neck, lungs, pancreas, and extremities.

parallel opposed

Often used when the depth of the target is uncertain.

parallel opposed l

The target volume extends throughout a particular area treated.

parallel opposed

Multiple angled fields are possible to set up.

parallel opposed

More reproducible

parallel opposed

Risks of tumor miss are reduced.

parallel opposed

The incidental irradiation of large volume of normal tissues situated within the fields

parallel opposed

High dose areas can be avoided by using a multiple field arrangement in which all beams encompass the target include different areas of surrounding normal tissues.

multiple field arrangements

Certain beam angles are prohibited due to the presence of critical organs in those direction

multiple field arrangements

The setup accuracy of a treatment may be better with what?

parallel opposed

The acceptability of treatment plan depends not only on the dose distribution but also on:

practical feasibility setup accuracy reproducibility of the treatment

Can be designed to produce uniform dose distributions.

multi field arrangements

What field is box technique

multiple field arrangements

Box technique is for what organ

pelvic tumor

Three field technique is for what organs

pancreas bladder rectum

The used of these is use to alter the dose distribution in beam.

wedge field

Originally designed to be used in the treatment of small shallow tumors..

wedge field

Rotation therapy

moving beam

Arc Treatment

moving beam

Combining Fixed and Moving-beam Technique.

moving beam

Treatment preparation

gross tumor clinical target volume planning target volume treated volume irradiated volume

The gross palpable or visible/demonstrable extent and location of malignant growth.

gross tumor volume

Is a tissue volume a demonstrable GTV and/or subclinical microscopic malignant disease must be eliminated.

clinical target volume

Contains the tissues that are to be irradiated to a specific dose according to a specified time-dose pattern.

planning target volume

Is the volume enclosed by an isodose surface, selected and specified by radiation oncologist as being appropriate to achieve the purpose of treatment.

treated volume

Is the volume of tissue that receive a dose considered significant in relation to tissue tolerance.

irradiated volume

Types of beam modification

Shielding Compensation Wedge filtration Flattening

Types of beam modification devices

Field blocking and shaping devices Compensators Beam spoilers Wedge filters Beam flattening Bolus Breast cone Penumbra trimmers Electron beam modification

Field blocking shaping filters

Shielding blocks Custom blocks Asymmetrical jaws Multi- leaf collimators

Refers to the material whose interactions with radiation beam mimic those tissue.

bolus

Bolus devices

Paraffin wax Vaseline gauze Wet gauze or towels Water bags

Bolus of a thickness equal to the depth of maximum dose eliminates WHAT of megavoltage photon beams.

skin sparing effect

It can also be used to compensate variations in contour surface contour to eliminate air gaps in cavities.

bolus

Skewed dose distribution.

compensator

Placed in the head of treatment unit, thus modifying the radiation beam to accommodate the contour of the patient.

compensator

Compensator devices

brass copper lead lucite

The dimension and shape of the compensator must be adjusted to account for

Beam divergenc Linear attenuation coefficient of the filter material and soft tissue Reduction in scatter

As the distance between the skin and compensator increase the thickness ratio what?

decreases

As the distance between the skin and compensator what? the thickness ratio decreases

increases

Compensator consideration

Compensator to surface distance (less than 20 cm) Field size Depth Beam quality

It is designed to change the isodose curve relative to the beam axis at specified depth to the patient. Wedge reduce the dose in areas of overlap between fields that have hinge angles. Less than 180 degrees.

wedges

Sizes of wedges

15, 30, 45 and 60 degrees

Wedges are made of

Tungsten, lead, steel

Wedge Placed how much from the skin surface

15 cm

Wedge Placed 15 cm from what

skin surface

Individual wedges - used in what?

cobalt

used in cobalt

individual wedge

Wedges

Individual wedges Universal wedges Dynamic wedges Virtual wedges Pseudo wedges

In wedge x and y is what

width, legth

Special beam modifiers where shadow trays made from lucite are kept at a certain distance from the skin

beam spoilers

Allow to transmit of predetermined percentage of the treatment beam to a portion of the treatment field and may be used throughout the course of the treatment.

transmission filter

Used to shape photon or electron fields, take several forms. Materials range from spent uranium to lead to lead alloys.

shielding blocks

Used to shape photon or electron fields, take several forms. Materials range from spent what

uranium to lead to lead alloys.

Full shielding blocks are constructed to transmit how much of the original beam

less than 5%

Cerrobend (lipowitz metal) melting point is what?

165 degrees F (74 degrees Celsius)

Its melting point 165 degrees F (74 degrees Celsius)

Cerrobend (lipowitz metal)

Bismuth transmit how many percentage

Leadtransmit how many percentage

26.7

Tin transmit how many percentage

13.3

Cadnium transmit how many percentage

Shielding blocks thickness

7.5 cm

Shielding blocks 9.4 g/cm3 at how many degrees

Shielding blocks how much at 20 degrees

9.4 g/cm3

Two types of shielding blocks

positive, negative

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