Non-radiation features of the TPS

Question 1

What are the non-radiation features of the TPS?

Answer 1

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

Question 2

Why do the non-radiation features need to be tested?

Answer 2

Bugs occur
Implamentations are different
Manufacturers don’t test everything

Question 3

What cause the early/acute complications of RT?

Answer 3

Cells with high turnover
Overdose increase the frequency and severity
Dominant factors: total dose, irradiated volume, location, duration

Question 4

What cause the late complications of RT?

Answer 4

Cells with slow turnover - can take >6months to present
Irreversible and slow progressing
Dominant factors: total dose, fraction size, dose rate

Question 5

What are the issues of underdosing?

Answer 5

Hard to detect
Only seen after a long time
Jeopardise tumour control

Question 6

What are the lessons from historical incidents?

Answer 6

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

Question 7

What are the steps for commissioning a TPS?

Answer 7

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

Question 8

What are the key principles for commissioning a TPS?

Answer 8

Establish what options the applications offer
Develop tests to evaluate the accuracy of features
Assess results against national/international guidelines, considering local requirements

Question 9

What aspect of the virtual patient needs to be checked?

Answer 9

What happens to the CT data before it is viewable

Question 10

What aspect of the patient orientation needs to be checked?

Answer 10

If there is any scaling to HU values

Check each clinically used orientation

Question 11

What are the potential errors in contouring tools?

Answer 11

Geometric inconsistency between orthogonal views
What happens at the limit of the ROI?
What happens between slices?

Question 12

What are the options used for interpolating contours at the top of the ROI?

Answer 12

OMP stops at final slice
Can add half the slice separation
Can add a standard capping structure

Question 13

How is a 3D surface made from a 2D contour?

Answer 13

Can use distance maps: each grid point contains shortest distance to 3D surface
3D VOI defined as the zero level iso-surface

Question 14

How do autosegmentation tools work?

Answer 14

Grey level thresholding

Gradient tracking

Question 15

What aspects need to be tested for volume growing tools?

Answer 15

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?

Question 16

What is MBS?

Answer 16

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

Question 17

How is the margin refined?

Answer 17

Using radius = margin (based on ROI surface) + distance to surface

Question 18

What are the image registration options?

Answer 18

Frame of refernce
Fusion
Deformable registration
PET-CT

Question 19

How is the treatment evaluated?

Answer 19

Cumulative DVHs to find the volume of an ROI irradiated with dose > D

Question 20

What need to be tested for DVHs

Answer 20

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

Question 21

What are the advanced display options available?

Answer 21

3D
Smoothing of CT data
Multiplanar reconstruction
DRRs
Image registration

Question 22

What needs to be considered for DRRs?

Answer 22

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

Question 23

How can DRR accuracy be established?

Answer 23

Use a phantom

Question 24

What are the outputs from the TPS?

Answer 24

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?