RT techniques

Question 1

summary of 3DCRT

Answer 1

medium @ treatment time
worst @ dose conformity and to OARs

Question 2

3DCRT

Answer 2

pelvic RT tend to be 3/4 fields
localised the tumour and target and how they change shape, density and location
abdominal tends to be three fields
a couch angle an help assist in avoiding organs reducing dose to healthy tissues

Question 3

conventional

Answer 3

limited number of fields
large volumes can be treated
immobilisation
margins added to CTV
MLC
vol-delineated
positional accuracy +/- 5mm
often co-planar

Question 4

what is therapeutic index

Answer 4

higher the dose, the higher the probability of giving a tumourcidal dose. The gap between the TCP and NTCP is the therapeutic index, we want to kill the tumour whilst minimising dose to normal tissues

Question 5

stereotactic

Answer 5

non-coplanar
precise VOI delineation
micro MLC
right set up margin
very small treatment volumes
precise positional accuracy +/- 1mm max
more field
high degree immobilisation

Question 6

SABRT

Answer 6

high doses to small volumes, precisely defined
limited normal tissue in the high dose region
required mm accuracy localisation and immobilisation
extreme hypo fractionation = 1-5 fractions

Question 7

what early stage cancers receive SBRT

Answer 7

prostate
liver
adrenal gland
lung
oligometastatic disease

Question 8

prostate SGRT

Answer 8

total margin between GTV-PTV = 3mm
verification via implanted gold seeds
7+ non coplanar beams > high conformity of high dose region
5 fractions = best toxicity profile

Question 9

describe PACE-B

Answer 9

36.25Gy in 5 fractions (7.25Gy/ fraction) = 85Gy conventional

Question 10

planning target goals for prostate SGRT

Answer 10

99% of PTV receives greater than or equal to 999% of prescribed dose
max = 107%
oars to contour: rectum, bladder, femoral head, small bowel

Question 11

DART

Answer 11

pretreatment plan is changed during treatment to account for observed anatomical changes in the target localisation or OAR
results in more account plan which is patient specific, changes are only implemented if within tol

Question 12

plan of the day

Answer 12

library of plans created, with a best fit plan being used based on online imaging
three images created at planning
daily CBCT, most appropriate is chosen
improve target coverage and lowers bowel dose

Question 13

replan

Answer 13

for more systematic changes, plan goes back to planning
plan changed to adapt to CTV changes on set
suitable fro random changes

Question 14

online adaptive therapy

Answer 14

CBCT based autosegmentation of contours and automated plan allows for fully adaptive treatment
potential imaging for internal margin reduction

Question 15

BEV

Answer 15

conforms and shapes the beam to the tumour, reducing toxicity and improving QOL

Question 16

summary for VMAT

Answer 16

best @ dose conformity, dose to OAR and treatment time

Question 17

VMAT

Answer 17

consists of 2/3 arcs per treatment
fewer arcs = less time
gantry and MLC move
dose rate varies
standard linac has a max of 600MU
if the gantry speed varies, this reduces the time
lateral fields are slower to avoid OARs

Question 18

similarities in VMAT + IMRT

Answer 18

dose coverage, homogeneity, conformity rates for PTV

Question 19

VMAT disadvantages

Answer 19

increased plan optimisation dose
extended 20% isodose

Question 20

VMAT advantages

Answer 20

reduced treatment times
50% isodose volumes, slightly better than IMRT
reduced MU

Question 21

IMRT

Answer 21

intensity varies across the portal, with more dose distribution in some area
modifying the intensity, has a relationship with the dose distribution
more beam angles
odd number of beams
POP rare
easier to avoid OAR
sharp dose gradients, sharp dose fall off

Question 22

differences in IMRT

Answer 22

MLC define non uniform beam intensity in each field
more gantry angles
fields planned as intensity maps
fields separated into segments
composite dose may/may not be homogeneous
inverse planning

Question 23

what is dose tracking

Answer 23

allows for an estimation is dose to be made across the structures, to determine whether a adaption is required
tracking the dose to VOI allows for beneficial adaptation
has the potential to improve accuracy by lowering exposure to OAR, reducing margin size and increasing conformity, so the structures receive the planned dose
improves therapeutic index, improved local control

Question 24

techniques for respiratory motion

Answer 24

breath-hold
active breathing control
real time VOI tracking
gating
4D planning

Question 25

higher dose to prostate =

Answer 25

increase in TCP

Question 26

halcyon

Answer 26

FFF
higher dose rate
leaves have twice the speed
gantry is x4 speed
more patient friendly
work load friendly

Question 27

what is step and shoot

Answer 27

when MLCs are static
series of static segmented subfields at each gantry angle, MLC position only changes during beam off
extends treatment time, easier to plan can be forward or inversely planned

Question 28

sliding window

Answer 28

MLC’s constantly moving at each angle creating dynamic boomlets
auto dynamic MLC during beam on
leaves are more variable to pre-defined positions
inversely planned

Question 29

limitations for IMRT

Answer 29

high target conformity: movement/error
risk of carcinogenesis
unexpected toxicity

Question 30

clinical indications for IMRT

Answer 30

complex/irregular shapes
concave targets
near critical structures
near an area previous to RT

Question 31

other applications for IMRT

Answer 31

local advanced
multiple sites simultaneously treated
different dose prescriptions at different sites
dose boost to TV with high recurrence risk (simultaneous boost for sub volumes )
deliberate dose in homogeneity
remove unwanted in homogeneous dose distribution

Question 32

what is dose is for high risk to malignancies and prostate cancer

Answer 32

> 76Gy

Question 33

VMAT (tomotherapy, halcyon, arc therapy)

Answer 33

high dose conformity, homogeneity
sharp dose gradients
sparing adjacent OAR from high dose regions
enables dose escalation (higher TCP and lower NTCP)

Question 34

what is a concave target (nodal volume) perfect for

Answer 34

IMRT