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SEMIFINALS - 3RD YEAR TRANSES > RADTHERA > Flashcards

RADTHERA Flashcards

1
Q

Dosimeters Divided into Two:

A
  1. Absolute dosimeters
  2. Secondary dosimeters
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2
Q

here the dose is determined without reference to another dosimeter. Eg: free air ionization chamber, specially designed spherical chambers of known volume, calorimeter, Fricke dosimeter.

A

Absolute dosimeters

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3
Q

these dosimeters require calibration against a primary standard. Eg: thimble chambers, plane parallel ion chambers, TLD’s, Diodes and Films.

A

Secondary dosimeters:

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4
Q

The national standard instruments for the standardization of absorbed dose are of two types:

A
  1. Calorimeters
  2. Free-air ionization chambers
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5
Q

for megavoltage photon and electron beams. Calorimeters are used to provide direct determination of absorbed dose.

A

Calorimeters

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6
Q

for lower energy photon beams from x-ray generators operating at up to 300 kV. These provide direct determination of air kerma from which the absorbed dose to water can be calculated.

A

Free-air ionization chambers

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7
Q

STANDARD CALORIMETER: the relationship between radiation dose and change in temperature is given by:

A

Dose (Gy)=C x δT

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8
Q

Dose (Gy)=C x δT: C is ___ and δT is ___

A

where C is the specific heat of the irradiated matter (the amount of energy needed to raise the temperature of unit mass of a substance through 1 degree, expressed in units of in 1kg C) and δT is the change in temperature in degrees Celsius. The equation above assumes no loss of heat to the surrounding environment or structures.

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9
Q

is an instrument used in the measurement of the roentgen according to its definition.

A

free-air ionization chamber

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10
Q

chambers are too delicate and bulky for routine use.

A

Free-air ionization chambers

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11
Q

their main function is in the standardizing laboratories where they can be used to calibrate field instruments such as a __

A

thimble chamber.

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12
Q

Radiotherapy treatment units, such as linear accelerators and KV therapy units, have in-built dose measuring instruments that monitor and determine the amount of dose delivered these instruments are known as ___

A

monitor chambers

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13
Q

__ are used to calibrate these monitor chambers so that each monitor unit delivers a known amount of radiation. These ___ may be used to determine not only the amount of radiation delivered, but also the pattern of deposition of energy within matter by measuring dose at different points within the matter. They may be used also to calibrate other dose measuring equipment designed for special purpose measurements such as __

A

field instruments; in-vivo dosimeters.

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14
Q
  • It works based on the Bragg –Gray Cavity theory
  • Bragg-Gray cavity theory relates the radiation dose in a cavity volume of material to the dose that would exist in a surrounding medium in the absence of the cavity volume.
A

THIMBLE CHAMBERS

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15
Q
  • is a thimble ionization chamber connected to a condenser.
  • A Victoreen condenser chamber, manufactured by Victoreen Instrument Company.
  • Condenser chambers are suitable for measuring exposure rate in air for relatively lower energy beams (__)
  • The thimble at the right-hand end consists of an approximately air equivalent wall (Bakelite, nylon, or other composition) with a layer of carbon coated on the inside to make it electrically conducting.
A

CONDENSER CHAMBER ; ≤2 MeV

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16
Q
  • In 1955, __ designed a chamber which provided a stable and reliable secondary standard for x-rays and y rays for all energies in the therapeutic range.
  • This chamber connected to a specific electrometer (to measure ionization charge) is known as the Baldwin-Farmer substandard dosimeter.
  • The original design of the Farmer chamber was later modified by ___ to provide better (flatter) energy response characteristics and more constancy of design from one chamber to another.
  • Actual dimensions of the thimble and the central electrode.
A

FARMER CHAMBER ; Aird and Farmer

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17
Q

are parallel-plate chambers with a variable electrode separation.
* They can be used in absolute radiation dosimetry (when embedded into a tissue equivalent phantom).
* He called this chamber an ___

A

EXTRAPOLATION CHAMBER

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18
Q

are similar to the extrapolation chambers except for the variable electrode spacing. The electrode spacing of the parallel-plate chambers is small (__mm) but fixed.

A

PARALLEL-PLATE CHAMBERS ; ~2 mm

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19
Q

The function of the __ is to monitor dose rate, integrated dose, and field symmetry. Since the chambers are in a high-intensity radiation field and the beam is pulsed, it is important to make sure that the ion collection efficiency of the chambers remains unchanged with changes in the dose rate.

A

ion chamber

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20
Q

Dose rate can change by a factor of __ as the collimator jaws are opened to maximum field size limits.

A

two or three

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21
Q

In other systems, the ___ consists of a set of attachable cones of various sizes.

A

auxiliary electron collimator

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22
Q

The term __, in a general sense, means the region, at the edge of a radiation beam, over which the dose rate changes rapidly as a function of distance from the beam axis.

A

penumbra

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23
Q

The ___, mentioned above, is the region irradiated by photons that are transmitted through the edge of the collimator block.

A

transmission penumbra

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24
Q
  • Photon fluence emitted by a point source of radiation varies __as a square of the distance from the source.
  • for external beam therapy has a finite size, the source to surface distance is usually chosen to be large (__ cm) so that the source dimensions become unimportant in relation to the variation of photon fluence with distance.
    the source can be considered as a point at large source to surface distances. Thus, the __from such a source varies inversely as the square of the distance.
A

inversely ; ≥80 cm; exposure rate or “dose rate in free space”

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25
Q

Percent depth dose ___with SSD because of the effects of the inverse square law.

A

increases

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26
Q

When the field is ___ that required for lateral scatter equilibrium, the dose rate __.

A

reduced below; decreases rapidly

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27
Q

__ a portion of the electron beam field, in general, produces changes in the dose rate and dose distribution. The magnitude of the change depends on the __, the __, and the ___.

A

Blocking; extent of blocking; thickness of lead; electron energy

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28
Q

In order to represent volumetric or planar variation in absorbed dose, distributions are depicted by means of __, which are lines passing through points of equal dose

A

isodose curves

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29
Q

isodose curves represent

A

levels of absorbed dose

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30
Q

isotherms are used for

A

heat

31
Q

isobars are used for

A

pressure

32
Q

The charts in the first category are applicable when the patient is treated at a constant source-to-surface distance (SSD) irrespective of beam direction. In the second category, the isodose curves are normalized at a certain depth beyond the depth of maximum dose, corresponding to the axis of rotation of an isocentric therapy unit.

A

isodose chart

33
Q

The dose variation across the field at a specified depth is known as the __
* It may be noted that the __ is defined as the lateral distance between the __isodose lines at a reference depth. This definition is practically achieved by a procedure called the __

A

beam profile; field size; 50%; beam alignment

34
Q

can be measured by means of ion chambers, solid state detectors, or radiographic films.

A

Isodose charts

35
Q

__ is the medium of choice for ionometric measurements

A

water

36
Q

useful in the calculation of dose inhomogeneities due to the differing composition of human tissues, can also be extracted from the CT data set

A

Electron density information

37
Q

The following volumes have been defined as principal volumes related to 3-D treatment planning:

A

gross tumor volume (GTV)
clinical target volume (CTV)
internal target volume (ITV) and
planning target volume (PTV)
Gross tumor volume:

38
Q

is the gross palpable or visible/ demonstrable extent and location of malignant growth”
__ is usually based on information obtained from a combination of imaging modalities (computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, etc.), diagnostic modalities (pathology and histological reports, etc.) and clinical examination.
The gross tumor volume (GTV) is the gross demonstrable extent and location of the tumor. It may consist of primary tumor, metastatic lymphadenopathy, or other metastases. Delineation of GTV is possible if the tumor is visible, palpable or demonstrable through imaging. GTV cannot be defined if the tumor has been surgically removed, although an outline of the tumor bed may be substituted by examining preoperative and postoperative images.

A

Gross tumor volume (GTV)

39
Q

is the tissue volume that contains a demonstrable GTV and/or sub-clinical microscopic malignant disease, which has to be eliminated. This volume thus has to be treated adequately in order to achieve the aim of therapy, cure or palliation”

A

clinical target volume (CTV)

40
Q

consists of the CTV plus an internal margin. The internal margin is designed to take into account the variations in the size and position of the CTV relative to the patient’s reference frame (usually defined by the bony anatomy); that is, variations due to organ motions such as breathing and bladder or rectal contents

A

Internal target volume

41
Q

is a geometrical concept, and it is defined to select appropriate beam arrangements, taking into consideration the net effect of all possible geometrical variations, in order to ensure that the prescribed dose is actually absorbed in the CTV”

A

planning target volume (PTV)

42
Q

is the distance from the source to axis of gantry rotation known as the ___

A

source-axis distance (SAD); isocenter

43
Q

Treatment machines incorporating gamma ray sources for use in external beam radiotherapy are called ___. They are most often mounted __, allowing the beam to rotate about the patient at a fixed SAD

A

teletherapy machines; isocentrically

44
Q

Modern teletherapy machines have SADs of ___

A

80 or 100 cm

45
Q

geometric field arrangements of various megavoltage machines, ranging from 60Co machines with an SAD of __ cm to high energy Linacs with an SAD of__cm

A

SAD of 80 cm ; SAD of 100 cm

46
Q

For parallel opposed equally weighted beams: the point on the central axis __ the beam entrance points.

A

midway between

47
Q

For parallel opposed unequally weighted beams: the point on the central axis at the __ of the target volume.

A

centre

48
Q

. A decrease in the depth dose of one beam is partially compensated by an __ in the other

A

increase

49
Q

The advantages of the parallel opposed fields are the __ of setup,

A

simplicity and reproducibility

50
Q

A disadvantage is the __ to normal tissues and critical organs above and below the tumor.

A

excessive dose

51
Q

allows for a very high dose to be delivered at the intersection of the beams an example of a DVH (Dose–volume histograms) for a rectum in the treatment of the prostate using a

A

four-field box technique.

52
Q

Normal (perpendicular) beam incidence on the patient with flat skin surface.
Bolus is a tissue equivalent material placed directly on the skin surface to even out the irregular patient contour and thereby provide a flat surface for normal beam incidence.

A

Perpendicular

53
Q

roduce a relatively concentrated region of high dose near the isocenter, but also irradiate a greater amount of normal tissue to lower doses than fixed field techniques. The target is placed at the isocenter, and the machine gantry is rotated about the patient in one or more arcs while the beam is on. It is a useful technique used mainly for prostate, bladder, cervix and pituitary lesions, particularly boost volumes.

A

Rotational techniques

54
Q

can be used together with conformal shielding to increase the healthy tissue sparing.

A

Standard beam geometries

55
Q

refers to a portal in which half of the beam has been blocked, as to have the junction point between two adjacent fields at the level of the central axis.
If split fields are employed both the lateral fields as well as the lower neck-supraclavicular portal are split (double split)

A

Split field

56
Q

is the dose is delivered continuously but at a lower dose rate. A method of administration of radiation by delivering it continuously over a relatively long period at a low absorbed dose rate

A

Protraction of radiation treatment

57
Q

is given over a period of weeks rather than in a single session resulting a better therapeutic ratio. However, to achieve the desired level of biological damage the total dose in a fractionated treatment must be much larger than that in a single treatment.

A

Fractionation of radiation treatment

58
Q

The basis of fractionation is rooted in five primary biological factors called the five Rs of radiotherapy:

A

Radiosensitivity
Repair
Repopulation
Redistribution
Reoxygenation

59
Q

(i)uses more than one fraction per day with a smaller dose per fraction

A

Hyperfractionation

60
Q

reduces the overall treatment time, minimizing tumor cell repopulation during the course of treatment.

A

Accelerated fractionation

61
Q

(continuous hyperfractionated accelerated radiation therapy) is an experimental programme used with three fractions per day for 12 continuous days

A

Chart

62
Q

is a form of periodic radiation therapy directed to the same area which is separated into two or more phases by a planned rest interval. The amount of irradiation given during each treatment and the time and number of rest periods vary, but the principle remains the same.
Split-dose irradiation designed to describe the capacity of a __from sublethal damage. For full recovery to occur, the time between such split doses must be at least as long as the cell generation time, usually__

A

Split-dose radiotherapy; cell to recover; 24 hours

63
Q

has been found by several investigators to be a useful and satisfactory approach to the treatment of many neoplasms. This approach appears to be most useful in older patients and in those who do not tolerate therapy well, but seems to be at least as effective as routine continuous radiotherapy with the added advantage of decreased morbidity and better toleration of therapy.

A

Routine split-course therapy

64
Q

aims to remove as much of the cancer as possible and extend the patient’s life expectancy. Radiotherapy may be used in the early stages of cancer or after it has started to spread. It can be used to: try to cure the cancer completely (curative radiotherapy) make other treatments more effective

A

Curative radiotherapy

65
Q

is used to prevent or reduce the risk of cancer cells to spread. It’s often used after surgery to reduce the risk that the cancer will come back. It can also be used to provide relief from pain and other symptoms of cancer.

A

Prophylactic

66
Q

focuses on providing relief of pain and symptom and supporting patients to improve their quality of life. Palliative radiotherapy aims to shrink cancer, slow down its growth or control symptoms. It doesn’t aim to cure cancer.

A

Palliative radiotherapy

67
Q

is applied over five to six weeks in daily fractions of 1.8–2.0 Gy to a total dose of 50–50.4 Gy.

A

Preoperative (neoadjuvant) conventionally fractionated RT

68
Q

can lead to the shrinkage of primary lesion and related lymph nodes with the potential advantage of downstaging.

A

Preoperative radiotherapy

69
Q

is often used after primary treatments, such as surgery, to lessen the chance of your cancer coming back.

A

Post Operative Technique (Adjuvant)

70
Q

(sometimes referred to as plesiotherapy, curietherapy or endocurie therapy) is a term used to describe the short distance treatment of cancer with radiation from small, encapsulated radionuclide sources. This type of treatment is given by placing sources directly into or near the volume to be treated. The dose is then delivered continuously, either over a short period of time (temporary implants) or over the lifetime of the source to a complete decay (permanent implants). Most common brachytherapy sources emit photons; however, in a few specialized situations b or neutron emitting sources are used.

A

Brachytherapy

71
Q

There are two main types of brachytherapy treatment:

A

1.Intracavitary, in which the sources are placed in body cavities close to the tumour volume;
2. Interstitial, in which the sources are implanted within the tumour volume.

72
Q

incorporating gamma ray sources for use in external beam radiotherapy are called teletherapy machines. They are most often mounted isocentrically, allowing the beam to rotate about the patient at a fixed SAD. Modern teletherapy machines have SADs of 80 or 100 cm.

A

Teletherapy machines

73
Q

The main components of a teletherapy machine are:

A

a radioactive source;
a source housing, including beam collimator and source movement mechanism;
a gantry and stand in isocentric machines or a housing support assembly in stand-alone machines;
a patient support assembly; and
a machine console

SEMIFINALS - 3RD YEAR TRANSES (5 decks)

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