Adaptive RT Flashcards
What is the definition of adaptive RT?
Use IGRT information to establish the dose to tumour and OARs on a regular basis (both intra an inter-fraction) during the treatment course
What are the categories of IGRT?
Simple - techniques don’t require serial imaging - gross error check
Complex - techniques involve significant serial imaging for systemic error correction - offline correction
Adaptive - techniques involving 3D image acquisitions so that the position of the field can be changed at the time of treatment - online correction
What are the 4 goals of adaptive RT?
Reduce uncertainties from shape change (pre-scheduled repeat planning CT)
Reduce uncertainties from shape change
Reduce uncertainties from shape change (pre-planned treatment imaging assessments)
Reduce uncertainties from shape change (React throughout treatment imaging session)
How are pre-scheduled repeat planning CTs used to reduce uncertainties?
Extended verification CT scan acquired at a pre-scheduled time during treatment suitably timed for planning or repeat planning CT acquired on planning CT scanner
Original plan recalculated on new image
Dose distribution evaluated - either accept or trigger a replan
How are changes responded to to reduce uncertainties?
Observe/suspect a change in patient shape
Perform extend verification CT or repeat planning CT
Original plan recalculated on image
Either accept or replan
What should be taken into account before triggering a replan?
Dose too high? Dose to OAR too high? Dosimetric criteria Clinical criteria Plan specific details Clinical presentation Patient specific judgement
How are pre-planned treatment imaging assessments used to reduce uncertainties?
RAIDER trial - use plan of the day for bladder treatments
Contour 6 isotropic PTVs in 0.5cm steps
Register with soft tissue adjustment - evaluate appropriate bladder and therefore PTV size - PTV has 2-3mm clearance around bladder
Select appropriate plan to be delivered
What are the issues with plan of the day techniques?
Bladder fills during delivery - shoul be accounted for in PTV margin
Increased workload of 6 plans for 1 patient
How do you ensure you’re treating using the selected plan? - 3 plans under same patient - scheduled on the day
How many fractions do you allow each plan?
What are the systems capable of reacting throughout a treatment session to reduce uncertainties?
Tumour tracking
VERO-Image based Dynamic MLC tracking
Cyberknife
What are the four options for reacting to shape changes during a treatment session?
Real time tumour tracking
Image based dynamic MLC tracking
Dosimetric assessment during treatment
Dosimetric modification during treatment
What is the problem with adapting treatment to tumour response?
Don’t know about any subclinical disease that is present
Could replan to cover new GTV and miss subclinical disease - reducing effectiveness of treatment
What can be used as biological guided adaptive RT markers?
F-18 FDG - cell metabolism marker
F-18 FLT - cell proliferation marker
What are the challenges for using biological guidance methods?
Thresholding of metabolic images for accurate contouring Multi-modality registration Inter-disciplinary intgration Inter-disciplinary training Inter-disciplinary collaboration
How are the different bladder sizes imaged in the RAIDER trial?
Patient voids bladder then drinks 350ml
CT scan acquired at 30 mins and 60 mins with no voiding in between
