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Rt Physics > Wk05 EBRT TX Planning > Flashcards

Wk05 EBRT TX Planning Flashcards

1
Q

What are the advantage of opposing fields over single field?

A
  • treat deeper lesions
  • lower hotspot
  • minimises chances of geometrical miss
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2
Q

In parallel opposing fields, maximum dose increases with ____________?

A
  • increasing thickness
  • decreasing beam energy
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3
Q

What is integral dose

A

Integral dose is a measure of the total energy absorbed in the treated volume. ( aka volume of low dose)

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4
Q

What are the 4 methods to achieve dose uniformity in adjacent fields arrangements?

A
  1. Angle fields to match divergence along beam edge
  2. Skin gap for uniformity at depth
  3. Half beam block
  4. Spoilers to moderate dose changes in a field junction region

Application: central nerves system radiotherapy

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5
Q

What are the advantages of 3D planning over 2D planning?

A
  1. More accurate
  2. Greater flexibility of beam arrangement
  3. Conformal treatment possible —> better treatment results
  4. Better assessment of dose distribution
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6
Q

Name the 5 treatment planning procedure

A
  1. Acquisition of patient image / contour
  2. Outlining target and normal structure
  3. Construction of radiation beams
  4. Calculation of dose distribution
  5. Display of dose + plan evaluation
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7
Q

What is the importance of immobilisation systems

A

Minimise the random error and systemic error during patient set up.

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8
Q

GTV?

A

Gross tumour volume
= visible extent and location of the malignant growth

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9
Q

CTV?

A

Clinical target volume
= sub clinical microscopic malignant disease + regional lymph nodes

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10
Q

IM?

A

Internal margin
= a margin to compensate expected movement and variations in size, shape and position of CTV

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11
Q

ITV?

A

Internal target volume
= CTV + internal margin which takes into account CTV variations in position, shape and size.

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12
Q

SM?

A

Setup margin
= a margin to account for uncertainties in patient positioning and alignment of the beams during planning and through treatments

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13
Q

PTV?

A

Planning target volume
= margin accounts for all possible geometrical variations and inaccuracies
= to ensure that the CTV receives the prescribed dose.

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14
Q

TV?

A

Treated volume
= volume enclosed by an Isodose surface that is selected by MO as being appropriate to achieve the purpose of treatment

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15
Q

IV?

A

Irradiated volume
= tissue volume which received a dose that is considered significant in relation to normal tissue tolerance

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16
Q

OAR?

A

Organ at risk
= normal tissue whose radiation sensitivity may significantly influence treatment planning and prescribed dose

17
Q

PRV?

A

Planning risk volume
= expansion of critical structures to increase avoidance regions

18
Q

What are the dose calculation algorithms that are commonly used?

A

Pencil beam convolution (PBC)
Analytical anisotropic algorithm (AAA) (eclipse)
Acuros XB (eclipse)
Collapse cone convolution (CCC) (Pinnacle, CMS, Xio)
Monte Carlo (MC) (Monaco)

19
Q

What are the 3 criteria of an ideal plan?

A
  1. High dose zone enclose the target volume
  2. Low dose to the neighbouring normal structures
  3. Uniform dose inside the target volume
20
Q

What is the use of dose volume histogram (DVH)?

A
  • check dose adequacy and uniformity in target volumes
  • extent and value of any hotspot in OARs
  • dose comparison between rival plans
21
Q

What is conformity index and its normal range?

A

Normal situation : CI = 1-2
CI>1 = normal tissue included in high dose
CI<1 = target volume is partially irradiated
Unacceptable: CI >2.5 or <0.9

22
Q

What is homogeneity index?

A

D2 = dose to 2% of PTV (max dose)
D98 = dose to 98% of PTV (min dose)
D50 = dose to 50% of PTV

HI = 0 (ideal homogeneity)

23
Q

What are the benefits of IMRT?

A
  1. Better normal tissue sparing and sharp dose fall-off —> reduce side effects without decrease local tumour control
  2. Can perform multiple simultaneous treatment (SIB = simultaneously integrated boost)
24
Q

What are the pros and cons of eclipse fluence-based optimisation?

A

Pros
- faster, interactive and offers better direct control (manual fluence editing)

Cons
- dose from optimal fluence is not real, often different from final dose calculations

25
Q

What variables can be adjusted during beam on in VMAT?

A
  • MLC positions
  • gantry speed
  • dose rate
  • collimator angle (elekta only)
26
Q

Why do we need additional QA for IMRT?

A
  • MLC motion complexity
  • transfer information from TPS to Linac
  • complex delivery
27
Q

Name 2 2D array detectors

A
  1. MapCheck
  2. Matrixx
28
Q

name 2 3D array detectors

A
  1. ArcCheck
  2. Delta4

Rt Physics (13 decks)

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