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CSB069 > Tomotherapy > Flashcards

Tomotherapy Flashcards

1
Q

What is tomo?

A
  • form of CT guided IMRT
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2
Q

How does tomo work?

A
  • 6MV photon
  • radiation delivered in helical manner
  • 64 binary MLC
  • max treatment width = 40cm
  • max treatment length = 160cm
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3
Q

What is the slip-ring gantry?

A
  • continous radiation through 360 degrees
  • MLC’s change every 7 degrees
  • max 64 beamlets per projection
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4
Q

What are the advantages of helical delivery?

A
  • by delivering dose in narrow rotating beam, high speed MLC and from multiple angles around the target
  • able to bend dose to conform tightly to the PTV and avoid OAR
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5
Q

What are the sim considerations for tomo?

A
  • all patient have CT sim
  • reproducible and stable
  • visually straight
  • good fit shell
  • vacbag for all patients
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6
Q

What are the disadvantages inside the treatment room?

A
  • noisy 78dB
  • cold 20C
  • pinch hazzard at top of bed
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7
Q

What are the advantages inside the treatment room?

A
  • personal control panel touch screens, auto load convenience
  • no applicators or heavy equipment thus no lifting
  • no gantry to rotate so eliminate crash hazard
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8
Q

What IGRT is used for tomo?

A
  • MVCT
  • mean energy 1MV
  • 0.5 to 2.5cGy per scan
  • slice thickness 2, 4, 6mm
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9
Q

What is a disadvantage of MVCT?

A
  • loss of distinction between soft tissue and bone
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10
Q

What is an advantage of MVCT?

A
  • improved imaging of high atomic number material (artifact)
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11
Q

What is the image registration process?

A
  1. sagittal: check pitch and sup-inf, ant-post
  2. coronal: check yaw and left-right
  3. transverse: check roll, left-right and ant-post
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12
Q

What 4 directions can be corrected for?

A
  • sup-inf
  • ant-post
  • left-right
  • roll
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13
Q

How is roll corrected for?

A
  • starting gantry angle changed
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14
Q

How is treatment delivered?

A
  • couch moves applied automatically
  • treatment time is set and small MU variations can occur day to day
  • patient monitored via CCTV
  • patient movement detected by couch wil stop treatment
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15
Q

What are the considerations for paediatrics?

A
  • low dose wash is not ideal
  • most require GA
  • able to offer retreatment of brain tumours previosly treated
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16
Q

What is a treatment consideration for long treatment fields?

A
  • need to take several MVCT as whole length not possible
17
Q

What setup changes are commonly made due to weight loss?

A
  • foam added where neck fat used to be

- daily MVCT to verifty foam and patient position

18
Q

How is tomo planned?

A
  • inverse planning

- a lot of contouring required

19
Q

How does tomo deliver treatment?

A
  • set number of beamlets available for the plan

- tomo assigns number of beamlets to each structure according to tolerance

20
Q

What is the average treatment time for H and N?

A

5 - 7 mins

21
Q

What is the average treatment time for TNI/CNS?

A

14 mins

22
Q

What are 6 planning aspects?

A
  • field width
  • pitch
  • modulation factor
  • compensation
  • blocks (directional vs complete)
  • priorities/importance /penalties
23
Q

What are some considerations with field width?

A
  • defined by primary collimator jaw
  • three settings: 1, 2.5, 5cm
  • smaller field widths improve dose modulation in longitudinal direction but increase treatment time
24
Q

What is pitch?

A
  • distance the couch travels per rotation of the gantry divided by the field width
25
Q

What does a tighter pitch increase?

A
  • number of active rotations that treat over a target length

- more beamlets available

26
Q

What does a pitch <1.0 mean?

A
  • sup and inf edged of the primary beam overlap
27
Q

Why is a tighter pitch commonly used?

A
  • helps with targets that are offset laterally as there is limited entry angles
  • allows you to maximise the MLC movement within the amount of treatment angles you use
  • reduces threading
28
Q

What is modulation factor?

A
  • refers to the limit of range of leaf intensity values allowed (how long MLC are open)
  • 1.0 = equal intensity value for all beamlets
29
Q

What does increasing the modulation factor allow?

A
  • better coverage
  • longer treatment time (slower gantry rotation)
  • potentially higher hotspot
30
Q

What are the two types of block?

A
  • directional

- complete

31
Q

What is a directional block?

A
  • the primary beam may pass through a directional-blocked structure if they pass through a target first
  • often used for shoulders in h and n
32
Q

What is a complete block?

A
  • primary beams cannot pass through the structure

- can be used for eyes in complex h and n or brain planning

33
Q

Once you begin planning what can you not change?

A
  • field weight
  • pitch
  • contour of any structure
  • overlap priority
  • use of structure unselected
34
Q

What is the optimal gantry period?

A
  • 20 seconds
  • indicates tomo working efficiency
  • allows reasonable treatment time
35
Q

What happens when a significant change is observed on an MVCT?

A
  • planner notified
  • plan adaptive calculation
  • RO Review
  • either replan or continue treatment
36
Q

What is the dose for a breast?

A

-50Gy in 25#

37
Q

What are the dose tolerances for combined lung, heart and spinal cord?

A
  • Lung: V30<13%
  • heart V27<12%
  • SC: max 35Gy

CSB069 (5 decks)

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