Non-radiation features of the TPS Flashcards
What are the non-radiation features of the TPS?
Virtual representations of the linac and patient ROI/segmenting Contouring tools/voume growing MBS, ABS ROI properties Dose visualistion Adaptive planning Dose tracking Fallback planning Radiobiological optimisation
Why do the non-radiation features need to be tested?
Bugs occur
Implamentations are different
Manufacturers don’t test everything
What cause the early/acute complications of RT?
Cells with high turnover
Overdose increase the frequency and severity
Dominant factors: total dose, irradiated volume, location, duration
What cause the late complications of RT?
Cells with slow turnover - can take >6months to present
Irreversible and slow progressing
Dominant factors: total dose, fraction size, dose rate
What are the issues of underdosing?
Hard to detect
Only seen after a long time
Jeopardise tumour control
What are the lessons from historical incidents?
Check TPS functionality to be used clinically Don't release untested features Don't ignore unusual side effects Don't deviate from procedure Don't ignore error messages
What are the steps for commissioning a TPS?
Understand the capabilities and limitations
Check dose calculation normalisation methods
Check treatment set-up parameters in TPS compared to the actual treatment machine
Check MU calculations
Check inhomogeneity corrections
What are the key principles for commissioning a TPS?
Establish what options the applications offer
Develop tests to evaluate the accuracy of features
Assess results against national/international guidelines, considering local requirements
What aspect of the virtual patient needs to be checked?
What happens to the CT data before it is viewable
What aspect of the patient orientation needs to be checked?
If there is any scaling to HU values
Check each clinically used orientation
What are the potential errors in contouring tools?
Geometric inconsistency between orthogonal views
What happens at the limit of the ROI?
What happens between slices?
What are the options used for interpolating contours at the top of the ROI?
OMP stops at final slice
Can add half the slice separation
Can add a standard capping structure
How is a 3D surface made from a 2D contour?
Can use distance maps: each grid point contains shortest distance to 3D surface
3D VOI defined as the zero level iso-surface
How do autosegmentation tools work?
Grey level thresholding
Gradient tracking
What aspects need to be tested for volume growing tools?
What happens for rapidly changing structures?
Does it depend on slice separation - what happens when grown volume = slice separation
What resolution can you grow to?
Does it support ATLAS based segmentation?
What is MBS?
A semi-automatic volume growing tool - based on biomechanical and statistical information about organs
Volumes are segmented using grey scale gradients and models on how organs change shape.
Can delineate multiple ROIs at once, increasing throughput
How is the margin refined?
Using radius = margin (based on ROI surface) + distance to surface
What are the image registration options?
Frame of refernce
Fusion
Deformable registration
PET-CT
How is the treatment evaluated?
Cumulative DVHs to find the volume of an ROI irradiated with dose > D
What need to be tested for DVHs
How the dose distribution is binned/sampled
How the volumes are sampled
How are the appropriate points selected for inclusion
How accurate are the dose calculations and ROI absolute volumes
What are the advanced display options available?
3D Smoothing of CT data Multiplanar reconstruction DRRs Image registration
What needs to be considered for DRRs?
How is resolution determined
What are the options for contrast
Can the apparent energy of the DRR be changed
Do the volumes and dose overlay the DRR
Can all gantry, collimator, and couch angles be supported
How can DRR accuracy be established?
Use a phantom
What are the outputs from the TPS?
Plan - how is the integrity of data transfer between application to R&V, and then to treatment machine
Referenc data for imaging - is the display interpolated and smoothed? What is exported?
