Adaptive Radiotherapy Flashcards
Reasons for Adaptive RT?
Organ motion
Anatomical change
Biological variation
What is Adaptive RT
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)
Types of Adaptive RT?
Patient position correction
Image guided radiotherapy
Modification to treatment plan
What are the three time frames for Adaptive RT?
Offline- between fractions
Online- immediately before a fraction
In real time during a fraction
What are the patient position modifications?
Modification of patient position
• Patient re-set up
• Change in specific set up instructions
• Modifications to patient specific immobilisation devices
How does IGRT work
Assess changes in patient position relative to treatment plan
• Adaptation via couch shifts to account for variation
What are some Patient organ motion detection?
4DCT capabilities (Elekta symmetry)
Patient motion detection (iguide)
Detection of correct floor rotation (Exatrac)
Video based systems (Varian RPM)
Limitations of IGRT?
Image guidance can not corect for non-rigid changes
What is the deformable image registration?
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
Limitation of deformable image registration?
There is no unique solution
• Similar voxels can be grouped differently based on different rules
What is the clinical problem with Bladder ART?
Organ motion
lead to generous margins 2-3cm
ART for bladder?
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
Clinical problem of Prostate ART/
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
ART for Prostate?
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
Imaging for prostate ART?
Current CBCT is suboptimal
Onboard MRI machine is desired
Clinical problem for Lung ART?
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
Respiratory motion of Lung ART?
<1cm to >2cm Affects accuracy of tumour delineation Increased side effects Tumour moving in and out of field Bones good surrogate for nodal disease
Pre treatment Lung Imaging/
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
Treatment delivery for Lung ART?
Active motion compensation techniques
Gating
Breath control
Tumour tracking
What are the two breathing control methods?
Varian RPM real time monitoring
ABC breath control
Tumour tracking?
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
Changes for Lung ART?
Tumour changes
Difficult to determine due to atelectasis or unhealthy lung
Surronding tissue change
biological and functional imaging for lung ART?
PET
SPECT
Ventilation and perfusion imaging
Benefits of FDG?
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
What is SPECT
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
What is ventilation/ perfusion scans?
The movement of air between the atmosphere and alveoli and the distribution of air
Perfusion: The movement of blood through though the pulmonary capillaries •
Clinical problem H&N ART?
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)
Use of adaptive RT in H&N?
Positioning errors
• Anatomical change
• Biological respons
Anatomic variation in H & N ART?
Weight loss
Parotid shifts medially
Dose gradients
Variation in literature for H & N ART?
Dosimetric impact
• Percentage of patients who will benefit
• Timing of intervention • Clinical outcomes
Biological adaptation for H & N ART?
Modfication of treatment
adaption based on assessment of early response
Define volumes that would benefit from dose escalation
Utilisation of MRI Linac
Limitation of Adaptive RT?
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
