dose fractionation in radiotherapy Flashcards
in the linear-quadratic model, what does alpha link to
single-stranded DNA breaks
in the linear-quadratic model, what does beta link to
double-stranded DNA breaks
in the linear-quadratic model, what does “the shoulder” link to
“sublethal” damage
what is the cell response to cell death caused by ionising radiation
- repairing sublethal damage
- reassortment to more radiosensitive phases
- reoxygenation
- repopulation
- redistribution
- radiosensitivity
why do we fractionate
to limit damage to surrounding tissues
what does biologically equivalent dose allow us to do
compare the potency of various fractionation regimens - alpha-beta ratios needed
what does the linear quadratic model describe
the relationship between total isoeffective dose and dose from 1 Gy-5/6 Gy
conclusions of the linear quadratic model
- late response in normal tissues
- early response in rapidly proliferating carcinoma
what is the LQM useful for calculating
change in total dose for an altered dose
dose needed for lymphomas and semiomas
40Gy or less
dose needed for glioblastoma multiforme
70Gy (currently lowered to 60)
what must be considered for palliative RT
short timing, convenience, cost, minimal side effects
RT for management of signs of progressive cancer
higher doses, more conformal techniques to prevent symptoms
what is oligometastatic disease
the midway between localised and metastatic disease
pros of SABR
safe, feasible, efficient
stereotaxia meaning
3D arrangement to touch
what is SRS
stereotactic radiosurgery
what is fSRT
fractionated stereotactic radiation therapy
what does SRS/SABR use to create a compact dose
intensity modulation
image guidance
motion control
stereotactic targeting
what are the 8 different fractionation regimes
- CHART
- Hyperfractionation
- conventional
- SIB
- Moderate hypofractionation
- Extreme hypofractionation
- SBRT
- SRS/ FSRT
advantage of hyperfractionation
more rapid increase in tolerance with decreasing dose for late tissues
what does accelerated RT aim to reduce
the protective effect of tumour cell repopulation
what does hypofractionation increase and what is it used for
increases late effects and is used for both curative and palliative care
how long should the gap be if you’re giving multiple fractions per day
6 Hrs
