OAR Limits, modelling retreatments and standard Radiobiological reporting Flashcards Preview

Year 3: Radiobiology > OAR Limits, modelling retreatments and standard Radiobiological reporting > Flashcards

Flashcards in OAR Limits, modelling retreatments and standard Radiobiological reporting Deck (13)
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1
Q

Why are OAR dose limits important?

A

Need to know the probability of doing harm to the patients - limits the dose and technique used to treat the patient

2
Q

What four pieces of information are needed to use dose limits in radiobiology calculations?

A

Total dose to OAR
Number of fractions OAR dose is given in
Effective volume of OAR that receives the dose
alpha/beta used in analysis in the source being used

3
Q

What are the main sources of data used for OAR dose limits?

A

Emami data
Data from clinical trials
QUANTEC data
Upcoming data

4
Q

What does the Emami data include?

A

Literature review up to 1991 for 28 dose limiting complications
Tabulated TD50/5 and TD5/5 - doses that give 50% and 5% NTCP at 5 years
Tabulated volume dependencies - partial irradiation of volume fraction v of organ where v = 1, 2/3, and 1/3
Fit of a volume dependence to a power law and calculation of NTCP using Lyman model

5
Q

What does the Emami 2013 paper include?

A

Summarised updates to his previous dose limits in light of QUANTEC data and new techniques

6
Q

What are the QUANTEC papers?

A

DVH driven outcome data for 16 critical organs - gives consensus guidlines and lit review

7
Q

How are the data sets in the QUANTEC papers presented?

A

Different summary charts as well as some overview papers and summary tables

8
Q

Why should the data in the QUANTEC papers not always be used directly?

A

Some data states fraction regime which is good
Some specify ‘standard fractionation’ to the tumour- could be between 1.8-2Gy/# - there is no fixed relationship between OAR and tumour doses so need to find out fraction regime used

9
Q

What is the formula for calculating the dose limit for the OAR locally from the QUANTEC papers and clinical trials?

A
X(1+(X/(nref.(alpha/beta))) = D(1+(D/(nlocal.(alpha/beta)))
Where X = dose in paper
nref = number of fractions in paper
D = local dose
nlocal = local number of fractions
10
Q

What needs to be considered for patients with previously treated areas?

A

If they have have one course or multiple courses before
What recovery has been made by the specific organ - literature gives organ specific retreatment outcomes and recommended limits

11
Q

What is the standard method of reporting radiobiology?

A

EQD2 or EQDX

12
Q

What is the Withers formula?

A

EQD2 = (D(1+d/(alpha/beta)))/(1+(2/(alpha/beta))) = D(((alpha/beta)+d)/((alpha/beta)+2))

13
Q

What is the new EQDX(alpha/beta) used for?

A

ICRU are working on it as a comprehensive and consistent framework for radiobiological modelling with EQD2 and BED as special cases