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Radiation Dosimetry > Final Exam > Flashcards

Final Exam Flashcards

1
Q

For TMR, where is the field size measured?

A

at treatment SAD

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2
Q

For TMR, where is the machine output measured?

A

at treatment SAD

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3
Q

What is the TMR equation?

A

Tumor Dose/ (MO)x(Sc)x(Sp)x(TMR)x(any aborption factor)

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4
Q

What is rotation therapy?

A

a treatment where the radiation source is moving around the patient during treatment

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5
Q

What is a full rotation defined as?

A

traveling 360 degrees

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6
Q

What a distance traveled less than 360 degrees?

A

Arc

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7
Q

What is it called when isocenter is placed 2.0-2.5 cm beyond the middle of the tumor during partial rotation?

A

Past pointing

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8
Q

Explain past pointing

A

During partial rotation, the isocenter is placed 2-2.5 cm past the middle of the tumor

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9
Q

What is an Arc

A

a rotation less than 360 degree

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10
Q

Define gantry speed

A

Monitor Units/Degrees in the arc (or rotation if 360 degrees)

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11
Q

What is the Clarkson technique and its function?

A

Calculation utilized to adjust the scatter air ratio for irregular (blocked) fields

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12
Q

What is the other name of the Clarkson technique?

A

Irregular Field Calculation

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13
Q

What is the Clarkson technique equation?

A

TAR= TAR0 + SAR

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14
Q

How many HVLs in order to transmit less than 5% of beam?

A

5 HVL

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15
Q

In new linac, what device is utilized to shield normal tissue?

A

MLC

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16
Q

What are the most cited irregular fields?

A

Mantle, Helmet and Inverted Y

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17
Q

What does the mantle field treat?

A

All lymph nodes about the diaphragm

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18
Q

What does the inverted Y field treat?

A

subdiaphrahmatic lymph nodes, can include spleen

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19
Q

What does the helmet field treat?

A

whole brain and all/part of the c-spine

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20
Q

What is cerrobend also known as?

A

Lipowitz Metal

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21
Q

What is the composition of cerrobend?

A

Bismuth, Lead, Tin and Cadmium

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22
Q

What is the ratio of cerrobend to lead?

A

1.25 cm of Cerrbond= 1 cm of lead

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23
Q

What is the advantage of using cerrobend over lead?

A

lower melting point

24
Q

What is a negative block and give example?

A

Negative block is central opening and peripheral blocking, Ex. Electron cut out

25
Q

What is a Positive block and give example?

A

Positive block is central blocking and peripheral opening, Ex. Photon Block

26
Q

What is a divergent block?

A

blocks have slanted edges to mimic beam divergence

27
Q

What is a non-divergent block?

A

blocks have straight edges

28
Q

When projecting the size of the block on the film tray or tray, what type of relationship does it have?

A

Direct Proportion

29
Q

What is the most accurate modality to utilize for treatment planning?

A

CT Scan

30
Q

What are the three directions of a CT scan image?

A

Coronal, Transverse/axial and Sagittal

31
Q

What is the most commonly utilized beam modifying device

A

Wedge

32
Q

What is a universal wedge?

A

centrally mounted wedge, can accommodate all field sized

33
Q

What is an individualized wedge?

A

seperate wedge for each beam width, toe of the wedge aligns with field edge, used on Co60 machines

34
Q

What is a dynamic wedge?

A

wedge effect by varying dose rate and mechanical motion of the collimator during the treatment

35
Q

What is a wedge angle?

A

Angle through which an isodose curve is tilted at the central ray of a beam at a specified depth.

36
Q

What is the range of the wedge angles?

A

15-60 degrees

37
Q

What is the wedge angle formula?

A

90-(.5 x Hinge angle)

38
Q

What is a hinge angle?

A

angle between the central ray of two fields

39
Q

What is the optimum hinge angle formula?

A

180-(2 x wedge angle)

40
Q

What is the defintion of a gap or field separation calculation?

A

calculation done to match abutting fields at some depth to reduce cold/hot spots

41
Q

What is the gap calculation equation?

A

Gap= ((F1/2) x (Depth/SSD1)) + ((F2/2) x (Depth/SSD2))

42
Q

Electrons are generally used for what type of treatment?

A

boost

43
Q

What is the rule of thumb used to determine the electron isodose line coverage to the deepest part of a tumor?

A 
Mev/4= 90% IDL
Mev/3= 80% IDL
Mev/2= 10% IDL
44
Q

What is the area of the 80-90% IDL called?

A

Therapeutic Range

45
Q

What is the area of the 10% IDL called?

A

Practical Range

46
Q

The therapeutic range covers what area?

A

80-90% IDL

47
Q

The practical range covers what area?

A

10% IDL

48
Q

What are isodose curves?

A

lines pass through points of equal dose in order to represent volumetric or planar variations in absorbed dose

49
Q

What are multiple isodose curves called?

A

Isodose chart

50
Q

What factors affect Isodose Curves?

A

Beam energy, Field Size, Source Size, Source Diaphragm Distance (SDD), AND Source to Skin Distance (SSD)

51
Q

What is penumbra?

A

the region at the edge of a radiation beam where the dose rate change rapidly

52
Q

Penumbra is located between what range of IDL?

A

20-90% IDL

53
Q

What is the penumbra formula?

A

s(SSD+depth-SSD)/SDD

54
Q

What is GTV and what does it include?

A

Gross Tumor Volume and Tumor or demonstrable disease extent

55
Q

What is CTV and what does it include?

A

Clinical Tumor Volume and GTV + Subclinical disease

56
Q

What is PTV and what does it include?

A

Planning Target Volume and CTV+ margins for setup uncertainties and patient/organ motion

Radiation Dosimetry (2 decks)

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