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CSB094 - RT Planning 4 > Wk 5 - Adaptive RT > Flashcards

Wk 5 - Adaptive RT Flashcards

1
Q

adaptive RT

A

changing the treatment plan delivered to a patient during a course of radiotherapy

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2
Q

what does adaptive RT account for

A
  • temporal changes in anatomy (tumour shrinkage, weight loss or internal motion)
  • changes in tumour biology/function (eg. hypoxia)
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3
Q

IGRT limitations

A

image guidance in isolation can not correct for non-rigid changes

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4
Q

IGRT advantage

A

provides rich 3D information which can be used as the basis for adaptive planning intervention - modification of the initial plan

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5
Q

adaptive RT can be implemented at three time points

A

offline - between fractions
online - immediately before a fraction
realtime - during a fraction

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6
Q

real-time adaptive RT workflow

A
  • technology to locate the target during real time
  • dose calculation during real time
  • technology to hit the target during real time
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7
Q

radixact synchrony

A

has integrated intrafraction motion management based on the synchrony to predict motion based on implanted fiducials or the tumour itself

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8
Q

bladder ART - clinical problem

A
  • organ motion
    • bladder is mobile, hollow organ that can change significantly in size, shape and position during treatment
  • leads to generous margins (2-3cm) and resultant irradiation of large amounts of surrounding healthy tissue
    • dose limiting toxicity to small bowel and bladder itself
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9
Q

bladder ART - prescription

A

50-66Gy

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10
Q

Bladder ART - IGRT

A
  • leads to reduction in required margins
    • eg. without IGRT 2cm margin is required to ensure 95% of CTV coverage. with IGRT, the margin was able to reduce to 1.2cm
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11
Q

bladder ART - online ART

A
  • daily pre-treatment CBCT
  • treatment staff select ‘plan of the day’
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12
Q

bladder ART - offline ART

A
  • adaptive PTV delineated based on information from first 5 fractions of CBCT
  • utilisation of patient-specific margins
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13
Q

prostate ART - clinical problem

A
  • size, shape and position of prostate is highly dependent upon state of bordering organs (rectum and bladder)
  • can lead to under or over dosage of prostate and/or overdosing of bladder and rectum –> increased side effects
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14
Q

prostate ART - offline ART

A
  • delivered dose and the variation of organs of interest is accounted for in the planning objective function –> dose distribution accomplished in the adaptive plan is optimised for the remaining treatments
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15
Q

prostate ART - online ART + IGRT

A
  • current onboard CBCT imaging is suboptimal for online guidance of prostate cancer treatment due to poor soft tissue contrast
  • the MRI linac enhances the online image guidance capability and subsequently improve treatment accuracy
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16
Q

lung ART - clinical problem

A
  • prognosis for NSCLC is poor
  • dose escalation restricted by surrounding dose limiting structures
  • respiratory motion and associated tumour movement major limitation
    • affects accuracy of tumour delineation
    • potential of increased side effects
    • potential of tumour moving in and out of treatment field
17
Q

how can ART help in lung cases

A
  • tumour delineation and margin selection
  • treatment delivery techniques
  • volumetric imaging during treatment responding to tumour and surrounding tissue changes
    • ART for dose maintenance
    • ART for normal tissue sparing
  • adaptation of treatment plan due to biological and functional response
    • ART for dose escalation
18
Q

lung ART - treatment delivery

A
  • active motion compensation techniques
    • gating
    • breathing control
    • tumour tracking
  • techniques adapt the treatment to maintain constant target position in the BEV when the beam is on
19
Q

lung ART - gating

A

imaging and treatment devices are periodically turned on and off, in phase with the patient breathing pattern, in order to restrict the range of positions of the tumour and internal anatomy during imaging and radiation delivery

20
Q

two primary methods of gating in lung ART

A
  • real-time monitoring of free-breathing
  • managing a long and reproducible breath-hold
21
Q

lung ART - real-time monitoring

A
  • Varian RPM
  • RPM system tracks the respiratory cycles of the patient through a reflective plastic box placed on the patient’s abdominal surface
22
Q

lung ART - breath control

A
  • active breathing control device (ABC)
  • used to suspend breathing at any pre-determined position along the normal breathing cycle
23
Q

lung ART - tumour tracking

A
  • dynamically shifting dose in space so as to follow the tumour’s changing position during free breathing

method should be able to do 4 things
- identify tumour position in real time
- anticipate tumour motion to allow for time delays in beam response
- reposition the beam
- adapt dosimetry to allow for changing lung volume and critical structure locations during the breathing cycle

24
Q

lung ART - biological and functional imaging

A
  • PET
  • SPECT
  • ventilation and perfusion imaging
  • can adapt the treatment plan based on biological response to treatment
    • boost areas of ‘active’ tumour
25
Q

lung ART - SPECT

A
  • single photon emission computed tomography
  • assess lung function
  • can be used to design and adjust treatment plan to limit dose to functional, healthy lung tissue
26
Q

lung ART - ventilation scans

A

the movement of air between the atmosphere and alveoli and the distribution of air within the lungs to maintain appropriate concentrations of oxygen and carbon dioxide in the blood

  • Can be used before, during and after treatment to design, adapt and assess treatment
27
Q

lung ART - perfusion scans

A

the movement of blood through the pulmonary capillaries

  • Can be used before, during and after treatment to design, adapt and assess treatment
28
Q

H&N ART - clinical problem

A
  • undergo considerable anatomical and tumour change during treatment

multifactorial reasons
- weight change
- change in size and shape of tumour and nodal disease
- change in OAR size and shape
- post operative chances (eg. oedema)

29
Q

H&N ART - use of ART

A
  • positioning errors
  • anatomical change
  • biological change
30
Q

limitations of ART

A
  • time and resource intensive process
  • more clinical outcomes studies needed
  • extensive re-contouring required
    • more automation
    • reliable deformable image registration tools
  • intrafraction motion
    • respiration and organ filling
31
Q

future directions for ART

A
  • advancing technology will help address workflow issues
    • on-board imaging technology
    • AI
    • deformable image registration
    • planning programs
    • treatment delivery programs
32
Q

adapt to position

A

based on rigid registration isocentre in the reference data is updated and retreatment plan recalculated to improve target coverage

33
Q

adapt to shape workflow

A

plan adaptation based on new anatomy using MRI and adapted contours. recalculated plan on online planning

CSB094 - RT Planning 4 (9 decks)

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