Treatment Planning

Question 1

What might you consider when planning a breast plan?

Answer 1

Energy - separation across the breast, do we need 10MV
Which breast - left breast need to think about cardiac shielding
Nodes - do we need to treat further out
Isocentre - must avoid collisions and be able to get acceptable images
Flash - want to open field out

Question 2

What would you consider when checking a plan?

Answer 2

Right patient - name, DOB, nhs no.
Right scan - date and time, right imaging system, right treatment orientation
Is registration okay if there is one
Are targets/OARs/PRVs all okay, including algebra
Are any support structures set to forced density if needed
Plan design: right modality/technique/machine/fractions/dose/median dose or dose at volume/isocentre appropriate
Optimisation: iterations before conversion/ sliding window sequencing/beams named right/shifts match/no segments and shape of segments/ treat margin/MU limit/dose grid
Evaluation: clinical goals right/max dose okay/does plan approval match pdf/instructions for imaging

Question 3

What would you consider when reviewing 4DCT?

Answer 3

Is the inherent registration between the 3DCT and 4DCT okay?
Are there any artefacts?
If there are artefacts, are they in the region of the PTV?
Is the motion of the tumour smooth and can be trusted?
What is the extent of the tumours motion?

Question 4

What do you consider when choosing an isocentre location?

Answer 4

Will the XVI imaging allow you to image everything you need to - target volumes and external
Will there be a collision between patient/couch etc and linac head

Question 5

Why do we do checking?

Answer 5

To check that there are no errors in the work that has been carried out and that the plan produced followed work instructions and is safe and appropriate

Question 6

Why do we need to do an independent MU check?

Answer 6

IR(ME)R means every plan needs an independent check

Question 7

When might we do individual QA?

Answer 7

Outside of segment/MU limits
Bespoke template
Different fractionation

Question 8

Why can we trust process-based QA instead of individual?

Answer 8

Combination of VMAT QA, class solution use, and verification.
For the first few plans of a new treatment type, we do process based and individual QA and results are compared, if there is good agreement between the two then we can trust that process-based method reflects individual QA results and can be trusted.

Question 9

What would you do if a plan failed its dose calculation check?

Answer 9

Check that it has definitely been done correctly
Send it to be delivered on the linac and measured
If this fails, basic troubleshooting (is it the right plan, is the measurement set up correctly)
If it still fails, deliver a standard plan and check that this passes (if this fails then it suggests problem with linac)
If this passes then it suggests a problem with the plan, could try and deliver on another linac, speak to an MPE, would not deliver it as is

Question 10

How is plan different when patient has metal hips?

Answer 10

Use OMAR to reduce metal artefacts
Force densities of metal hips to titanium
Don’t put dose through hips
Image quality will be worse

Question 11

What would be an ideal plan?

Answer 11

Deliver a dose of radiation to tumour that would kill it without delivering any dose anywhere else

Question 12

How would MU calculation deliver in a lung which is inflated vs deflated?

Answer 12

Inflated lung has more lung tissue which is less dense
Less tissue to attenuate the beam
Plan will be slightly hotter at depth

Question 13

Define conformal vs VMAT treatment

Answer 13

Conformal treatment is made up of a number of fixed beams which are conformed to the target volume, there is no movement of gantry or MLCs, and no variation in dose

VMAT delivers while the gantry moves, the MLCs move, the dose varies

Question 14

Advantages of VMAT over conformal?

Answer 14

Can have much more conformal dose distribution - can have convex distribution
This allows normal tissue to be spared, spare OARs, potentially reduced toxicity
Can have deliberately non-uniform dose distribution: can deliver more than one dose level

Question 15

When would you choose conformal over VMAT?

Answer 15

In patients where you want to completely spare tissue: patients with a single kidney where you want to deliver nothing to other kidney; patients with pacemaker where you want to spare pacemaker
Palliative patients, can get a conformal plan through faster, less planning

Question 16

Why use POP for breast over VMAT?

Answer 16

Can completely spare much more tissue if only using a POP.
VMAT would deliver exit dose to lungs/heart and this can be avoided

Question 17

Error at treatment 2 vs end of treatment?

Answer 17

Don’t want to delay treatment ending or have gap in treatment delivery
Fraction 2 of many, still have time to re-scan/re-plan and this may be preferred
End of treatment, may be okay depending how dramatic the problem is

Question 18

What are the advantages of collapsed cone over MC and PB

Answer 18

MC: less computationally intensive, can be computed quicker and with less powerful computers
PB: can account for lateral scatter and inhomogeneities, can therefore be used more reliably

Question 19

What type of set up errors could happen?

Answer 19

Systematic set up error: one which is propagated through the entire process
Random set up error: one which occurs at one fraction and won’t be repeated

Question 20

Give examples of some set up errors

Question 21

Where are GTV/CTV/PTV defined?

Answer 21

ICRU 50

Question 22

What is the ITV and where is it defined?

Answer 22

ITV = CTV + IM (internal margin)
Accounts for motion of CTV in patient, but does not account for setup uncertainties
ICRU 62

Question 23

What makes a good radiotherapy plan?

Answer 23

Uniform dose to PTV (ICRU recommends 95-107%)
95% isodose conforming closely to PRV
Critical doses to radiosensitive organs not exceeded and significant doses avoided
Integral dose kept to a minimum