Personnel dose reduction for Y90 microspheres liverdirected radioembolisation: from angiogram suite to patient
ward
Poster No.:
B-1248
Congress:
ECR 2015
Type:
Scientific Paper
Authors:
M. W. M. Law, K. K. Wong, W. K. Tso, H. F. V. Lee, M. Y. Luk;
Hong Kong/HK
Keywords:
Radiation physics, Radioprotection / Radiation dose, Interventional
vascular, Experimental, Dosimetry, Technical aspects,
Radioembolisation, Dosimetric comparison, Occupational /
Environmental hazards
DOI:
10.1594/ecr2015/B-1248
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Page 1 of 9
Purpose
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Y microspheres radioembolization is an emerging treatment modality for treatment of
liver malignancies [1]. Radioembolisation involves placing a radioactive material, tiny
resin or glass beads called microspheres directly at the tumor site under the guidance of
interventional radiology technique. With better understanding to the dose-response of the
90
treatment, there is a trend to adminster higher Y radioactivity for better patient efficacy
[1], raising the concern in occupational radiation dose received by medical personnel
caring for this new patient service [2]. Although there are local guidelines and regulations
regarding the safety use of radioisotopes in hospitals, any practical means to further
reduce occupational radiation dose to staff and exposure to nearby individuals is highly
desirable in order to comply with the 'as low as reasonably achieveable' (ALARA) principle
[3].
Images for this section:
Fig. 1: A lead lined blanket is used to cover the thorax and abdominal region of patient
undergone Y90 radioembilization.
Page 2 of 9
Methods and materials
Y90 is pure #-emitting isotope of average energy of 0.9 MeV, a maximum radiation
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range of 11 mm in tissue and of half life of 64 hours. Following treatment of Y
microspheres, patients become a source of radiation that could potentially affect other
persons around them via Bremsstrahlung emission [4]. Therefore safety precautions
must be considered to keep the dose to other individuals as low as reasonably achievable.
Because Bremsstrahlu`ng emission is in the form of #-radiation, lead apron type blanket
is useful to reduce the bremsstrahlung radiation.
A lead lined blanket of size 60 cm x 64 cm, weight 4 kg and of lead equivalence of
0.5 mm has been routinely used to cover the patient abdomen and thorax region after
radioembolization procedure in our institution. Patients were tolerable to the size and
weight of the blanket. This kind of blanket is commercially available and as presented in
this report, it was made from a retired lead apron. The blanket is warped with sterilized
plastic bag and its weight is tolerable to patient.
Radiation dose rates at 10 cm above patient abdomen surface and at the position of
interventional radiologist pressing the puncture site were measured with a calibrated
radiation survey meter (Fluke, model 451P, OH, USA) with and without the blanket in
place (Table 1).
Wilcoxon' t-test for paired samples was used to compare the difference in the measured
dose rates when using the lead lined blanket or not. The software used was Statistica
version xx (StatSoft, Tulsa, OK, USA). Values of p # 0.05 were considered to be
statistically significant
Results
90
Table 1 shows the dose rates, normalised by the patient administered Y microsphere
radioactivity, measured at the position of the interventional radiologist and at 10 cm above
the patient abdomen with and without being covered by the lead lined blanket. There has
been a dose reduction of a factor of > 2 with the use of the blanket. At the radiologist
Page 3 of 9
position during pressing the puncture site after radioembolisation, the average dose rate
has been measured as 1.32 µSv/(hr GBq). The average infused Y90 radioactivity for
our patients is 2.1 GBq. The radiologist thus received 0.92 µSv during pressing the
puncture site on his hands and arms that are not radiation shielded by lead apron. Since
the radiologist wears a lead apron of the same lead equivalence of the lead lined a
blanket, he actually would receive a body dose of 0.4 µSv under his lead apron due
to the Bremsstrahlung radiation from the patient after radioembolisation, comparable to
the hourly background radiation rate of about 0.3 µSv in our institution area. The same
radiation dose measurements have been calculated for nurses and porters nursing and
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transporting the patient respectively after Y radioembolisation treatment with the use
of the blanket (Table 2), showing occupational dose is indeed very minimal.
90
While radiation safety considerations in Y radioembolisation have been described
in detail for patient dosimetry accuracy, interventional radiology room radiation
contamination prevention and scenarios for radioemolised patients in contact with their
family [5], there is not much available in literature for dose reduction for medical
professionals involved in the procedure. Using a blanket type lead apron of 0.5 mm
lead equivalence with size and weight tolerable to patient comfort, it has been shown
that the Bremsstrahlung radiation emitted from patient can be reduced by more than
a factor of 2 in order to comply with the ALARA principle in radiation protection. This
90
dose reduction is useful for the concern to administer higher Y radioactivity for better
patient treatment efficacy. Generally, there are local recommendations and regulations
regarding the safety use of unsealed radioactive substance in hospitalization and on
90
patient release. Our institutional radiation safety regulation requires Y treated patients
of greater than 1.5 GBq should be accommodated in a single room ideally with private
toilet facility. Sometimes this cannot be achieved due to insufficient isolation ward or
there is no such facility in some hospitals but
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Y radioemboliation has to be performed.
We attempt to solve this resource problem by allocating the
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Y treated patient at a
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corner bed in a common ward. To justify that other patients at the vicinity of the Y
radioemboised patient would be exposed unnecessarily, the lead lined blanket is used
to cover the radiolembolised patient abdomen. The exposure rate at 1m is calculated to
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be 1 µSv/hr (assumed 2.1 GBq infusion). If the distance between the Y patient and the
patient adjacent to him is maintained at 2 m, the exposure rate would then be 0.25 µSv/hr
which is about the same background radiation level in our institution area. In other words,
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the Y patient would not expose unnecessarily radiation exposure to the next patient if
a lead lined blanket and distance as far as 2 m are followed.
Page 4 of 9
Indeed,
90
Y microspheres treated patients represent an even lower radiation safety risk
for nearby individuals because there is no biologic elimination of
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Y as the microspheres
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remain fixed in liver, tumor and lung [4-5]. There are two types of Y microspheres
commercially available, namely glass microspheres and resin microspheres [6-7]. The
glass spheres are not known to be present in any body fluid, whereas trace amounts of
90
Y radioactivity may be excreted in the urine of resin microsphere treated patients for the
first 24 hours. Therefore for glass microsphere treated patients, they can use the toilet
facility in the common ward as usual because their urine would not contain any radioactive
content. For resin microsphere treated patients, they are advised to flush the toilet twice
after use. In other words, radioembolised patients can use common toilet facility as other
non-radiation patients do.
Images for this section:
Fig. 1: A lead lined blanket is used to cover the thorax and abdominal region of patient
undergone Y90 radioembilization.
Page 5 of 9
Table 1: Normalized average dose rate measured at the interventional radiologist
performing puncture site pressing and at 10 cm above patient abdomen with and without
the blanket used.
Page 6 of 9
Table 2: Occupational dose estimation per procedure with the use of blanket covered
on patient thorax and abdomen after 90Y microspheres radioembolisation; interventional
radiologist has the role of puncture site pressing; nurse has the role of patient transfer
from X-ray couch to patient stretcher; porter has the role of transporting the patient from
interventional radiology room to ward. The estimated time is referred to our institution
workflow.
Page 7 of 9
Conclusion
A simple but practical measure of using a lead lined blanket not only further reduces
occupational dose to personnel providing patient service for the radioembolisation
procedure but also solves limited resource of isolation ward.
Personal information
a
a
a
b
b
M Law, KK Wong, WK Tso, V Lee, MY Luk
a
b
Department of Radiology and Clinical Oncology,
Queen Mary Hospital, Hong Kong
References
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Page 8 of 9
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