Abstract
A uniform distribution of yttrium-90 (90Y) microspheres throughout
the entire liver has always been assumed for dose calculation in
treating hepatic tumours. A simple mathematical model was formulated
which allows estimation of the activities of a therapeutic dose of
90Y microspheres partitioned between the lungs, the tumour and the
normal liver, and hence the radiation doses to them. The doses to
the tumour and normal liver were verified by intra-operative direct
beta-probing. The percentage of activity shunted to the lung and
the tumour-to-normal tissue ratio (T/N) were obtained from gamma
scintigraphy using technetium-99m-labelled macroaggregated albumin
(MAA) which simulates the 90Y microspheres used in subsequent treatment.
The intrahepatic activity was partitioned between the tumour and
the normal liver based on the T/N and their masses determined from
computerized tomography slices. The corresponding radiation doses
were computed using the MIRD formula. The estimated radiation doses
were correlated with the doses directly measured using a calibrated
beta-probe at laparotomy by linear regression. The radiation doses
to the tumour and the normal liver, estimated using the partition
model, were close to that measured directly with coefficients of
correlation for linear regression: 0.862 for the tumours and 0.804
for the normal liver compartment (P<0.001). The partition model permits
a distinction between the radiation doses received by the tumour
and the normal liver to be made and the doses thus estimated are
close to the actual doses received. The optimal doses to the tumour
and normal liver and hence the required quantity of 90Y microspheres
to be administered can be easily predetermined.
- 99m
- aged;
- aggregated
- albumin,
- brachytherapy,
- carcinoma,
- diagnostic
- dosage;
- dose-response
- effects;
- female;
- hepatocellular,
- humans;
- imaging/radiotherapy;
- liver
- liver,
- lung,
- male;
- methods;
- microspheres;
- middle
- models,
- neoplasms,
- radiation
- radiation;
- radioisotopes,
- radionuclide
- radiotherapy
- relationship,
- tc
- technetium
- theoretical;
- therapeutic
- use
- use;
- yttrium
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