TBI Flashcards
what is TBI used for
acute/chronic leukaemia
relapsed lymphoma
non malignant but life threatening: anaplastic anaemia
advanced disseminated, resistant disease: neuroblastoma (aggressive solid tumour of childhood)
what is the aim of TBI
kill all malignant cells
suppress immune system minimise GvHD
what is the target volume
all immune system cells + haem tissue
what is the main dose limiting structure
lung V20 30%
why is TBI good
it eradicates all malignant disease in the BM, chemo doesn’t fully deplete the BM, BBB prevents this
what is the conditioning regime
chemo + TBI
what is done after chemo
an allogenic SCT
what type of dose is it
homogenous and independent of the blood supply
what is TBI important for
the conditioning regime prior to the SC for haem malignancies i.e acute leukaemia and lymphoma
what does TBI accomodate
complete engraftment through BM depletion if not done, they are likely to reject the transplant. It immunosuppresses the pt to prevent rejection of the transplant/ donor bone marrow
what sites can TBI reach that chemo cant
scar tissue, skin surface, sanctuary sites
what is needed to treat the whole body
complex modality which delivers a uniform dose (+/-10%) of radiation to the entire body - heterogeneous
referral for TBI
BMT following MDT + relevant investigations
counselled in clinic [part of obtaining consent]
suitability for TBI
cardiovascular fitness + dose to organs
women under 36 should be counselled regarding their increased risk of breast cancer, should be referred to high risk breast screening programme
consent for TBI
RCR RT form
16+ and lack capacity should fill an all wales consent form 4
form should be kept with RT trt prescription sheet
RT is also authorised on WCP
request form by practitioner
clinical responsibility of TBI
review pt and approve for TBI
explain the procedure
obtain informed consent
pacemaker and ICD
prescribe to pt midline @ level of axillae
authorised eIRMER trt
ensure optimal medical management of pt and that each fraction is given in a timely manner
bookings for TBI
2 slots per month
blocks out trt machine
pt becomes an inpatient, remain in an isolation room until their last trt
what is the pt prep prior to TBI
consent: awareness on toxicities and risks
ward visit
visit trt unit and staff
key radiographer: explains procedure, answers qu and addresses concerns
what are the radiographer responsibilities
team liases with the consultant and medical physics and chemo ward
team ensures TBI is carried out
act within limits of their knowledge, skills and experience
most senior member is responsible in checking preg status
what are the medical physics responsibilities
ensuring dosimeters are prepped for each fraction
specifiying MU, brass compensators and measurement sites for each fraction
measurement + calc of pt dose, recorded on eIRMER
calc is independently checked
what is the TBI technique
lat POP @ extended FSD
4.5m to midline
12Gy in 6 fractions, 2 a day with a 6 hour gap
10MV
what angle is the gantry on
86 not fully lateral or 274
what is the coll head on
45 degrees to give a diamond shape
what is the field size
38x38 = varian
40x40 = elekta
if the couch was close to the wall what would that cause
an increase in scatter
what are the accessorises
acrylic/perspex screen [act as bolus: max dose to skin surface]
where is the trolley positioned
in line with the couch lasers, attached to the TBI bed with the 4.2m black line marked on the floor
what is the pt position
supine: head on curved sponge
arms by side: hand clasped, shielding bottom part of lung
head needs to be straight
pt squashed, knees bent
fairly free set up
all positions are noted so can be reproduced
dosimetry
probes need to be positioned directly opposite each other to give an accurate reading
brass is a compensator, sheets are used with a set thickness
what are the standard measurements
shoulder: 40cm
hip: 30cm
feet: 10cm
what happens if the measurements are wrong
cause lead to radiation pneumonitis
low dose TBI
single exposure
part of the conditioning regime
split into two parts to allow medical physics time to calculate the dose, MU left and changes to brass thickness
how long dose a single exposure take
4 hours
if a third calc is needed it will take another hour
pt advised to go to the toilet during the second calculation, pt will then need to be re-set up and diodes replaced
what are the low exposure ref points
2Gy
how much is the first part
40%
how many diodes at each position
at least one
what are the low dose fields
rt lat x3 lt lat x3
what is the dose for lymphomas
as radiosensitive
2Gy single exposure
where do centres prescribe to
max lung dose some prescribe to pelvis
what will happen if there is a gross difference between remaining MU and brass compensator
2 re-calculations
whats the dose for the ALL-RIC trial
8Gy in 4
what is the dose for specific BM transplants
14.4Gy in 6, 2x a day
what is the dose for umbilical transplants
4Gy in 2 in 2 days
what is the dose for a reduced intensity allogenic SCT
2Gy in 1
what is the varian MU/min
300
what is the elekta MU/min
320 (in mosaiq 350)
what is the total MU
2100/2600
how many MU can be delivered in one go
1000, which is split into three for each field
what does fractionation do
spares late damage
affects normal tissue toxicity
what is implications for single exposure
greater normal tissue damage
what does dose rate influence
normal tissue toxicity
early toxicities
nausea + vomiting
diarrhoea (1/3 pts)
circulating platelets [risk of haemorrhage]
circulating WBC [neutropenic sepsis - 5% mortality due to this or pneumonitis]
photophobia
conjunctival oedema
dry eye syndrome
xerostomia
parotitis (swelling of parotid glands, jaw pain)
pancreatitis
skin erythema (except 20-22MeV)
headache
hyperpyrexia (not common after 24 hrs)
what are the intermediate toxicities
radiation induced interstitial pneumonitis
moist desquamation
somnolence syndrome
- drowsiness, headache, anorexia (6 wks post)
alopecia
immunodeficiency
- defective T and B cells
heaptic-veno-occlusive disease
- jaundice, hepatomegaly and ascites
- had a 50% mortality rate [occurs in 25% of pts]
why do we destroy a pt immune system
to reduce the risk of GvHD, due to the T cell depletion of donor BM
what are the late toxicities
infertility
menopausal symptoms
endocrine failure - thyroid no longer functioning, no metabolism if no medication is given
growth impairment [likely with a single fraction]
osteoporosis + aseptic necrosis
intellectual impairment
pulmonary bronchiolitus obliterans [popcorn lung- narrowed airways]
hyper-pigmentation
early cataracts [5-30%]
hepatic/renal damage
carcinoma induction: lymphomas/solid tumours
what happens with higher doses
incidence rates increase for inducing carcinomas
what does toxicity depend on
dose
single exposure: around 2nd hour
fractionated: 2nd/3rd fraction [approx half way]
what is the advice for returning back to normal
careful eating and drinking
libido reduced for months
can socialise after 3-6 months
avoid travelling aborad for a year
avoid sunburn for two years
