Adaptive Radiotherapy

Question 1

Reasons for Adaptive RT?

Answer 1

Organ motion
Anatomical change
Biological variation

Question 2

What is Adaptive RT

Answer 2

changing the radiation treatment plan delivered to a patient during a course of radiotherapy to account for:
•  Temporal changes in anatomy (e.g. tumor shrinkage, weight loss or internal motion)
•  Changes in tumor biology/function (e.g. hypoxia)

Question 3

Types of Adaptive RT?

Answer 3

Patient position correction
  Image guided radiotherapy
Modification to treatment plan

Question 4

What are the three time frames for Adaptive RT?

Answer 4

Offline- between fractions
Online- immediately before a fraction
In real time during a fraction

Question 5

What are the patient position modifications?

Answer 5

Modification of patient position
•  Patient re-set up
•  Change in specific set up instructions
•  Modifications to patient specific immobilisation devices

Question 6

How does IGRT work

Answer 6

Assess changes in patient position relative to treatment plan
•  Adaptation via couch shifts to account for variation

Question 7

What are some Patient organ motion detection?

Answer 7

4DCT capabilities (Elekta symmetry)
Patient motion detection (iguide)
Detection of correct floor rotation (Exatrac)
Video based systems (Varian RPM)

Question 8

Limitations of IGRT?

Answer 8

Image guidance can not corect for non-rigid changes

Question 9

What is the deformable image registration?

Answer 9

Finding geometrical correspondences between imaging data sets (2D/3D/4D) that differ in time, space, modality

Commonly used in adaptive radiotherapy workflow due to its efficiency in adapting contours required for replanning

Question 10

Limitation of deformable image registration?

Answer 10

There is no unique solution

•  Similar voxels can be grouped differently based on different rules

Question 11

What is the clinical problem with Bladder ART?

Answer 11

Organ motion

lead to generous margins 2-3cm

Question 12

ART for bladder?

Answer 12

IGRT for reduced margins
Online - Daily pre treatment CBCT
Plan of the day

Offline
Adaptive PTV delineation based on first 5 fractions
Utilisation of patient specific margins

Question 13

Clinical problem of Prostate ART/

Answer 13

Size, shape and position of prostate is highly dependent upon state of bordering organs (rectum, bladder)
•  Can lead to under or over dosing of prostate and/or overdosing of bladder and rectum increased side effects

Question 14

ART for Prostate?

Answer 14

Offline-Use CT for adaptive plan of dose to rectum, prostate and bladder

Online
Direct beam aperture modification for CRT

Online beam aperture modification to online measurement of prostate and seminal vesicle deformation

MLC segment adjustment

Question 15

Imaging for prostate ART?

Answer 15

Current CBCT is suboptimal

Onboard MRI machine is desired

Question 16

Clinical problem for Lung ART?

Answer 16

prognosis for NSCLC poor
Dose escalation studies are promising
dose escalation restricted by dose limiting structures
IMRT and VMAT promising limited to geometric uncertainty
Respiratory motion

Question 17

Respiratory motion of Lung ART?

Answer 17

<1cm to >2cm
Affects accuracy of tumour delineation
Increased side effects
Tumour moving in and out of field
Bones good surrogate for nodal disease

Question 18

Pre treatment Lung Imaging/

Answer 18

Acquiring 4DCT
Mean position, size, shape and trajectory can be more accurately determined
•  Delineation of a patient-specific ITV (internal target volume)
•  Can result in larger target volumes

Question 19

Treatment delivery for Lung ART?

Answer 19

Active motion compensation techniques

Gating
Breath control
Tumour tracking

Question 20

What are the two breathing control methods?

Answer 20

Varian RPM real time monitoring

ABC breath control

Question 21

Tumour tracking?

Answer 21

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

Question 22

Changes for Lung ART?

Answer 22

Tumour changes
Difficult to determine due to atelectasis or unhealthy lung
Surronding tissue change

Question 23

biological and functional imaging for lung ART?

Answer 23

PET
SPECT
Ventilation and perfusion imaging

Question 24

Benefits of FDG?

Answer 24

Monitor tumour response in NSCLC

Therapy induced changes in tumour FDG uptake

Non responding patients at high risk for radiation induced toxicity

Adapt plan based on biological response to treatment

Question 25

What is SPECT

Answer 25

Single photon emission computed tomography
•  Assesses lung function
•  Can be used to design and adjust treatment plan to limit dose to functional, healthy lung tissue

Question 26

What is ventilation/ perfusion scans?

Answer 26

The movement of air between the atmosphere and alveoli and the distribution of air

Perfusion: The movement of blood through though the pulmonary capillaries •

Question 27

Clinical problem H&N ART?

Answer 27

H&N cancer patients can undergo considerable anatomic and tumour change during treatment

Weight change •  Change in size and shape of tumour and nodal disease •  Change in OAR size and shape •  Post-operative changes (e.g. oedema)

Question 28

Use of adaptive RT in H&N?

Answer 28

Positioning errors
•  Anatomical change
•  Biological respons

Question 29

Anatomic variation in H & N ART?

Answer 29

Weight loss
Parotid shifts medially
Dose gradients

Question 30

Variation in literature for H & N ART?

Answer 30

Dosimetric impact
•  Percentage of patients who will benefit
•  Timing of intervention •  Clinical outcomes

Question 31

Biological adaptation for H & N ART?

Answer 31

Modfication of treatment
adaption based on assessment of early response
Define volumes that would benefit from dose escalation
Utilisation of MRI Linac

Question 32

Limitation of Adaptive RT?

Answer 32

Patient specific margins
Plan of the day
Extensive re-contouring required 
Variation in opinion on patient selection
Variation on timing
Resource and time intensive
Sophisticated tools in development