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CSB093 > Hybrid Breast > Flashcards

Hybrid Breast Flashcards

1
Q

What is the (1) field arrangement for hybrid treatment planning?

A

(1) 4 beams
- 2 tangential open fields without wedging (right anterior oblique + left posterior oblique)
- 2 tangential IMRT fields (right anterior oblique + left posterior oblique)

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2
Q

What is the rationale for IMRT fields?

A
  • IMRT fields act as wedging to reduce hot spots in corners of breast/chest wall (and increase dose homogeneity)
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3
Q

What is the rationale for hybrid treatment planning (i.e. open fields) compared IMRT?

A
  • conformal IMRT does not allow for breast/chest wall inter-fraction variation (i.e. change in size and/or shape due to shrinking or swelling from hormones or side effect of radiation therapy and change in position)
  • conformal IMRT dose not allow for breast/chest wall intra-fraction variation (i.e. motion due to respiration)
  • complex IMRT increases number of MUs (or peripheral and whole-body patient dose)
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4
Q

Why is wedging not used for open fields where patients are treated in DIBH?

A
  • wedging increases DIBH time > 20-25 seconds
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5
Q

What POI are required for breast hybrid treatment planning?

A
  • CT reference point
  • isocentre
  • reference point for open fields
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6
Q

What OAR contours are required for breast hybrid treatment planning?

A
  • lt and rt lung

- heart

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7
Q

What is the rationale for bolus (i.e. external + bolus) for breast hybrid treatment planning?

A
  • to deliver dose to skin surface
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8
Q

What percentage of the dose prescription (40 Gy in 16 #) is prescribed in (1) open fields and (2) IMRT fields?

A

(1) 60-80% of dose prescription to open fields (24 Gy in 16 # to reference point for open fields)
(2) 40-20% of dose prescription to IMRT fields (16 Gy in 16 # to ROI mean of breast/chest wall objective)

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9
Q

Why is dose prescribed to ROI mean of breast/chest wall objective compared to breast/chest wall in IMRT fields?

A
  • breast/chest wall objective = breast/chest wall avoid exterior of contracted external/external + bolus to avoid build-up of dose on skin surface
  • breast/chest wall objective can be trimmed 0.5 cm from posterior border line to remove hot spots in corners of breast/chest wall
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10
Q

What is the rationale for maximum dose objective in IMRT fields?

A
  • to reduce global maximum dose
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11
Q

What are the IMRT parameters for IMRT fields?

A
  • max iterations = 30
  • convolution dose iteration = 10
  • maximum number of segments = 8
  • minimum segment area = 9
  • minimum segment MUs = 10
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12
Q

What is the (1) optimisation type, (2) allow jaw motion, (3) use as current jaw max and (4) split if necessary for IMRT fields?

A

(1) optimisation type = DMPO
(2) allow jaw motion = no
(3) use current jaw as max =
yes
(4) split if necessary = no

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13
Q

What is the (1) optimisation type, (2) allow jaw motion, (3) use as current jaw max and (4) split if necessary for open fields?

A

(1) optimisation type = none
(2) allow jaw motion = yes
(3) use current jaw as max =
no
(4) split if necessary = yes

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14
Q

What are considerations for isocentre placement in hybrid treatment planning?

A
  • position isocentre in the centre of posterior border line

- position isocentre close enough to CT reference point (< 10 cm) to ensure collision with contralateral arm

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15
Q

What is the collimator angle for open fields?

A
  • 0-degrees (to rotate MLCs in left/right direction)
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16
Q

What is the rationale for posterior border = 0 cm and anterior border = + 2 cm overshoot?

A
  • to ensure PTV coverage if variation in breast/chest wall size, shape or position
17
Q

What are considerations for trouble shooting to reduce hot spot/s in breast/chest wall for hybrid treatment planning?

A
  • adjust breast/chest wall objective to exclude hot spots in corners of breast/chest wall
  • decrease Gy value of uniform dose to reduce hot spot
  • move reference point to move hot spot
  • consider 10 MV on open fields with compromise of skin sparing
18
Q

How would you create anterior = + 2 cm overshoot in IMRT fields?

A
  • evaluate control points and combine control points that are similar
  • add skin flash (shift MLC leaves + 2 cm) to control point 1 to create anterior overshoot in IMRT fields
19
Q

What are the challenges for heart shielding in breast/chest wall hybrid treatment planning?

A
  • challenge to decrease dose to heart (or shield heart) without compromise of PTV coverage
  • RO could accept decreased PTV coverage if PTV is more superior and PTV coverage compromised is more inferior

CSB093 (6 decks)

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