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Dosimetry Physics 1 > Field Shaping and Craniospinal Irradiation > Flashcards

Field Shaping and Craniospinal Irradiation Flashcards

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1
Q

What is the shape of a field that utilized just x-rays jaws alone for collimation?

A

Rectangular

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2
Q

How can fields of irregular shaped be created?

A

Secondary Blocking or MLC’s

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3
Q

What are some device examples of secondary blocking?

A

Lead or Cerrobend Block

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4
Q

What is the material utilized for custom blocks?

A

Lipowitz Metal (Cerrobend)

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5
Q

What is the composition of Lipowitz Metal/Cerrobend?

A

Bismuth, Lead, Tin and Cadmium

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6
Q

What is the main advantage of Cerrobend?

A

Low melting point as opposed to Lead

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7
Q

What is the toxic element in cerrobend?

A

Cadmium

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8
Q

What is the ratio of Cerrobend to Lead?

A

1 cm of lead = 1.21 cm of Cerrobend

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9
Q

Positive Block

A

The Blocks are put in place to block out a structure within the inner field (Island block, lung blocks)

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10
Q

Negative Blocks

A

Blocks that are utilized to conform to a structure/shape (MLC conforming)

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11
Q

What are Multi-Leaf Collimators?

A

system of large amount of collimator blocks or leaves that are automatically and independently to generate a field of any shape

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12
Q

What is the typical amount of MLCs?

A

60-80 Pairs

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13
Q

What is size of the individual leafs?

A

0.5 - 1 cm leaves

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14
Q

What is the Collimation system for Varian?

A

Upper Jaw, Lower jaw and MLC

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15
Q

What is the Collimation system for Elekta?

A

MLC, Lower Jaw

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16
Q

What is the Collimation system for Siemens?

A

Upper Jaw, MLC

17
Q

Size of the physical pneumbra is impacted by _________ from the target

A

MLC Distance

18
Q

Does a shorter distance from the target to the MLC leafs create greater or lesser pneumbra?

A

Greater

19
Q

What is the interleaf transmission less than?

A

3%

20
Q

What is intraleaf leakage?

A

Leakage through the leaf itself

21
Q

What is interleaf leakage?

A

Leakage between the leafs

22
Q

What are the two important factors for MLC leaves?

A
  1. Leaves must overlap to prevent any interleaf transmission

2. Leave are focusing in the orthogonal plane and incorporate divergence into design

Dosimetry Physics 1 (6 decks)

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