Adaptive RT Flashcards
What is ART?
- technique aims to customise each patients treatment plan to patient-speicific variation by evaluating systematic and random variation
What are the time points for ART?
- offline: between fractions
- online: immediatley before fraction
- in real time: during fraction
What are the patient positioning ART?
- patient re-setup
- change in setup instruction
- change to immobilisation device
What are the IGRT ART?
- image taken prior to treatment to assess change in patient position and adapt couch position
What are the organ motion detection systems?
- elekta symmetry (4DCT)
- iGuide (patient movement)
- exactrac (floor rotations)
- varian RPM (breathing)
What is a limitation of IRGT?
- image guidance in isolation can not correct for non-ridig changes
What is an adantage of IGRT?
- provides righ 3D information which can be used for adaptive planning intervention
What is deformable image registration?
- finding geometrical correspondence between imaging data sets that differ in time, space and modality
- used in ART workflow due to efficiency in adapting contours required for re-planning
What is the clinical problem with bladder organ motion?
- bladder is mobile, hollow and can change size, shape and position significantly during treatment
- require large margins (2-3cm) which increase dose to OAR especially small bowel
What is the bladder ART?
- daily pre-treatment CBCT
- chose plan of the day (small medium and large)
- do offline adaptive PTV based on frist 5#
What is the cinical problem with prostate?
- size, shape and position is highly dependent on bladder and bowel
- can lead to over and under dosing of OAR and PTV
What is the online and offline ART for prostate?
- online: direct beam apeture modification so field shape of prostate and SV definition
- offline: delivered dose and organ variation accounted for and plan adapted for reamining fractions
What is the clinical problem with lung?
- outoe is poor and require dose escaltion but limited due to respiratory motion
What ate the ART for lung?
- pre treatment: 4DCT for mean size, shape and trajectory
- breahting control during treatment
- gating
- tumour tracking
What is gating?
- allows treatment device to periodically turn off and on depending on stage of breathing cycle
- RPM or ABC
What is tumour tracking?
- dynamically shifts dose to follow tumour position during free breathing
What is the clinical problem with H & N?
- patients undergo significant anatomic change during treatment which has impact on dose distribuition
- weight loss, change in PTV and OA, oedema
What is the position variation ART for H & N?
- image feedback
- quatify dosimetric error from setup error and adapt each fraction by taking into account dose accumulated over entire course and adjust prescription accordingly
What is the anatomical variation for H & N?
- parotid shift medially and decrease in size
- magnitude of effect depends on location to high dose region and OAR
What are the limitations of ART?
- patient specific margins: depends on no. of initial observations
- plan of the day: mutliply planning and staff training intensive
- extensive re-contouning required
- variation in opinion on which patient need ART
- variation in opinion on timing of ART
- resource and time intensive: workflow
What is the use of FDG-PET imaging for lung?
- may allow predication of tumout response or radiation induced lung toxcitity
- eary detection of non-responding patient can decrease cost and toxcitity for patient
- can adapt plan based on which area of lung is most functioning and aviod dose to that area
What are the 4 steps for tumour tracking?
- identify tumour position in real-time
- anticipate tumour motion to allow for time delays in beam reponse
- reposition the beam
- adapt dosimetry to allow for changing lung volumes and critical OAR and critical stucture location during the breathing cycle
